SECTION 3B - DIAGNOSIS - VT SEDAN WITH
ACCESSORY FITTED LPG
3.1 PREREQUISITES TO DIAGNOSIS AND TROUBLESHOOTING
PRELIMINARY SYSTEM REQUIREMENTS
Prerequisites before proceeding with system checks are:
Ensure that sound earth connections are available for all functioning components, particularly at the body earth
connection (fender panel inner stud, adjacent to the battery).
Ensure the battery is in good condition and adequately charged (above 12.5 volts) before carrying out any
electrical checks.
SAFETY REQUIREMENTS
Disconnect the battery when carrying out work which involves the risk of an electrical short circuit.
Do not touch mechanical components during function checks, to avoid the risk of a hand being caught in the
mechanism.
CHECKING EQUIPMENT
TECH 2 scan tool.
A digital multimeter, with a minimum 10 Megohm impedance MUST be used when undertaking any electrical
checks on these systems.
Exercise care when taking readings from wiring harness connectors. It is preferred that the back probing method
with individual connectors is employed wherever possible, to avoid terminal damage and subsequent connection
failure.
When carrying out wiring checks as directed to by the diagnostic charts, rather than probe terminals and connectors
with incorrect sized multimeter connections, use the adaptors contained in connector test adaptor kit KM-609. This
will prevent any possibility of spreading or damaging wiring harness terminals.
IMPORTANT:
ENSURE THAT THE IGNITION IS TURNED OFF AND THE BATTERY EARTH LEAD IS DISCONNECTED
BEFORE ANY TEST THAT REQUIRES DISCONNECTION OR RECONNECTION OF ANY OF THE PCM
CONNECTORS.
When checking the complete system, the exact order of the test steps should be observed.
If the required nominal value is not achieved in any stage, then the problem must be rectified before
proceeding further.
Unless the multimeter being used has an auto ranging function, check that the correct range, as specified, is
selected before the test is carried out.
Testing of the system will involve gaining access to specific wiring harness connectors. For the location of
these connectors, refer to Section 4 WIRING DIAGRAMS.
Techline
3.2 GENERAL INFORMATION
The procedures outlined in the LPG VEHICLE PRELIMINARY DIAGNOSTIC CHART MUST be carried out first
whenever diagnosing a problem in a LPG vehicle.
The LPG system is designed to operate in LPG mode when LPG has been selected via the fuel mode switch. When
diagnosing the LPG system, unless otherwise directed. Ensure that the LPG mode has been selected, there is LPG
in the LPG cylinder and the manual service valve is turned 'ON'.
When LPG has been selected via the fuel mode switch the PCM will operate in the LPG mode if the operating
parameters sensed by the PCM permit the switching to the LPG mode.
Before any diagnostic procedures are carried out on the LPG system you must first confirm that the vehicle
operates on petrol without any problems and there are NO DIAGNOSTIC TROUBLE CODES stored in the PCM
memory. This can be achieved by following the LPG VEHICLE PRELIMINARY DIAGNOSTIC CHART in this
Section.
After the LPG vehicle preliminary diagnostic procedure has been carried out, an ON-BOARD DIAGNOSTIC
SYSTEM CHECK must be performed and any diagnostic trouble code that has been logged in the PCM memory
must be rectified and all diagnostic trouble codes cleared before you confirm any problem with the LPG system.
When carrying out the diagnostic procedures refer the to the fold out wiring diagrams, refer Section 4 WIRING
DIAGRAMS in this Section.
3.3 LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. If the Check Powertrain Lamp illuminates, the PCM is being powered up. If the Check Powertrain Lamp does
not illuminate you should refer to the ON-BOARD DIAGNOSTIC SYSTEM CHECK, in the VT Series Service
Information CD.
2. Ensures TECH 2 is functioning correctly.
3. Checks if TECH 2 can communicate with the PCM. If Tech 2 cannot communicate with the PCM you should
refer to PCM DIAGNOSTICS in the VT Series Service Information CD.
4. Checks if the PCM can operate in the LPG mode.
5. Checks if the LPG switch is operating correctly.
6. Checks the operation of the LPG lamp.
7. Checks if the engine will operate on petrol.
8. Checks if the engine will crank when LPG has been selected.
9. Checks if the engine will run when LPG has been selected.
10. If the engine backfires when operating on LPG, go to the 3.9 ENGINE BACK FIRES ON LPG diagnostic chart
in this Section.
11. If the engine lacks power, is sluggish or has poor performance, refer Diagnostic Chart 3.10 POOR
PERFORMANCE, SLUGGISH OR POOR FUEL CONSUMPTION WHEN OPERATING ON LPG in this
Section.
12. If the fuel gauge does not operate correctly on when petrol or LPG has been selected via the fuel mode switch,
refer Diagnostic Chart 3.12 FUEL GAUGE DOES NOT OPERATE in this Section.
STEP ACTION YES NO
1. 1. Turn ignition ON.
2. Does the Check Powertrain
Lamp illuminate?
Go to Step 2. Refer ON-BOARD
DIAGNOSTIC SYSTEM
CHECK, Section 6C1-2A
in this Service
Information CD.
2. 1. Turn ignition OFF.
2. Install TECH 2 to DLC.
3. Turn ignition ON.
4. Push power button on TECH
2.
5. Does TECH 2 power up
(screen will illuminate display
TECH 2)?
Go to Step 3. Refer TECH 2
DIAGNOSIS,
Section 0C TECH 2
in this Service
Information CD.
3. 1. With TECH 2 still connected
and ignition on, press the
ENTER key then select
Diagnostics / model year / VT
Commodore / Engine / V6
LPG, follow the instructions
on the Tech 2 screen.
2. Does TECH 2 display PCM
system identification
information (PROM ID)?
Go to Step 4. Refer ON-BOARD
DIAGNOSTIC SYSTEM
CHECK, Section 6C1
in this Service
Information CD.
4. 1. With TECH 2 still connected
and ignition on,
select / F2: Data Display / F0:
All Data / Scroll to LPG Fuel
Enabled.
2. Does TECH 2 display LPG
Fuel Enabled YES?
Go to Step 5. Refer 3.4 DOES NOT
OPERATE ON LPG, in
this Section.
STEP ACTION YES NO
5. 1. With TECH 2 still connected,
scroll to Fuel.
2. Select LPG via the fuel mode
switch.
3. Does Fuel display on TECH 2
change from Petrol to LPG?
Go to Step 6. Refer 3.5 FUEL MODE
SWITCH DOES NOT
OPERATE, in this
Section.
6. 1. Ignition ON, select LPG via
the fuel mode switch.
2. Does the LPG lamp in the
switch illuminate?
Go to Step 7. Refer 3.6 LPG LAMP
DOES NOT OPERATE in
this Section.
7. 1. Select Petrol via the fuel
mode switch.
2. Will the engine crank and
start immediately the key is
turned from off to start (no
delay)?
Go to Step 8. Refer ON-BOARD
DIAGNOSTIC SYSTEM
CHECK, Section 6C1
in this Service
Information CD.
8. 1. Select LPG via the fuel mode
switch.
2. Will the engine crank
immediately the key is turned
from off to start (no delay)?
Go to Step 9. Refer 3.7 ENGINE DOES
NOT CRANK in this
Section.
9. 1. Does engine crank and run
on LPG? Go to Step 10. Refer 3.8 ENGINE
CRANKS DOES NOT
START ON LPG in this
Section.
10. 1. Does engine backfire when
operated on LPG? Refer Diagnostic
Chart 3.9
ENGINE
BACKFIRES ON
LPG in this
Section.
Go to Step 11.
11. 1. Does engine lack power,
sluggish or have poor
performance when operating
on LPG?
Refer Diagnostic
Chart 3.10 POOR
PERFORMANCE
, SLUGGI SH OR
POOR FUEL
CONSUMPTION
WHEN
OPERATING ON
LPG in this
Section.
Go to step 12
12. 1. Does fuel gauge operate
correctly? LPG system
operating
correctly.
Refer Diagnostic Chart
3.12 FUEL GAUGE
DOES NOT OPERATE in
this Section.
3.4 DOES NOT OPERATE ON LPG
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. The LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK must be the first step when diagnosing any LPG
system problem.
2. The PCM will not operate in the LPG mode if it is fitted with the incorrect PROM. Refer to the latest technical
publications or spare parts information (PartFinderΤΜ) for the correct PROM application.
3. When the ignition is turned on, battery voltage is applied to terminal E11 of the PCM. This enables the PCM to
operate in either the Petrol or LPG mode. If battery voltage is not applied to PCM terminal E11 the PCM will
only operate in the Petrol mode.
4. This test confirms that the PCM connector terminal retention is not causing the problem. The terminal retention
should always be checked before a PCM is replaced.
STEP ACTION YES NO
1. 1. Has LPG VEHICLE
PRELIMINARY DIAGNOSIS
CHECK been performed?
Go to step 2 Perform LPG VEHICLE
PRELIMINARY
DIAGNOSIS CHECK.
2. 1. Is the PCM fitted with the
correct LPG PROM? (Refer
2.19 PROM in Section 2 of, VT
Sedan With Production LPG).
Go to step 3. Install the correct LPG
PROM.
Verify repair.
3. 1. Ignition ON.
2. Check for voltage at PCM
terminal E11 connector YB194
circuit 39 (Pink/Blue wire).
3. Is battery voltage present?
Go to step 4. Repair open in circuit 39
between fuse F14 and
PCM terminal E11.
Verify repair.
4. 1. Check PCM connector
terminal retention.
2. Is terminal retention OK?
Replace PCM
refer to Section
6C1-3 SERVICE
OPERATIONS -
V6 ENGINE in
this Service
Information CD.
Verify repair.
Repair terminals.
Verify repair.
3.5 FUEL MODE SWITCH DOES NOT OPERATE
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. The LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK must be the first step when diagnosing any LPG
system problem.
2. Tests operation of fuel mode switch.
3. Checks for voltage at the fuel mode switch. If voltage is not present, circuit 39F is open between the fuel mode
switch and fuse F14. If voltage is present there is an open circuit between the fuel mode switch and PCM
terminal A9.
4. This test checks for an open in the fuel mode switch circuit 2.
5. This test confirms that the PCM connector terminal retention is not causing the problem. The terminal retention
should always be checked before a PCM is replaced.
STEP ACTION YES NO
1. 1. Has an LPG VEHICLE
PRELIMINARY DIAGNOSIS
CHECK been performed?
Go to step 2 Perform an LPG
VEHICLE PRELIMINARY
DIAGNOSIS CHECK.
2. 1. Test fuel mode switch.
Refer 2.22 FUEL MODE
SWITCH TEST in Section 2 of,
VT Sedan With Production
LPG.
(Note: refer 2.4 FUEL MODE
SWITCH in Section 2B of this
Section to remove switch).
2. Is the fuel mode switch OK?
Go to step 3. Replace fuel mode
switch.
3. 1. Ignition ON.
2. Check for voltage at the fuel
mode switch connector LP5
circuit 39F (Pink/Blue wire).
3. Is battery voltage present?
Go to step 4. Repair open in circuit 39
between fuse F14 and
fuel mode switch.
4. 1. Check for open in circuit 2
(Violet wire) between fuel
mode switch and PCM
terminal A9.
2. Is circuit open?
Repair open in
circuit 2 between
fuel mode switch
and PCM
terminal A9.
Go to step 5.
5. 1. Check PCM connector
terminal retention.
2. Is terminal retention OK?
Replace PCM
refer to Section
6C1-3 SERVICE
OPERATIONS -
V6 ENGINE in
this Service
Information CD.
Verify repair.
Repair terminals.
Verify repair.
3.6 LPG LAMP DOES NOT OPERATE
NOTE:
The LPG lamp on VT Series Models with accessory fitted LPG systems is located in the fuel mode switch, not the
instrument cluster.
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. The LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK must be the first step when diagnosing any LPG
system problem.
2. Checks for voltage at the fuel mode switch. If voltage is not present, circuit 39G is open between the fuel mode
switch and the splice joint.
3. This test checks the continuity of the fuel mode switch earth circuit for an open in the fuel mode switch circuit 2.
4. This test confirms that the PCM connector terminal retention is not causing the problem. The terminal retention
should always be checked before a PCM is replaced.
STEP ACTION YES NO
1. 1. Has an LPG VEHICLE
PRELIMINARY DIAGNOSIS
CHECK been performed?
Go to step 2 Perform an LPG
VEHICLE PRELIMINARY
DIAGNOSIS CHECK.
2. 1. Ignition ON, LPG selected.
2. Ignition OFF
3. Remove instrument panel
facia to gain access to the fuel
mode switch, refer 1A3
INSTRUMENT PANEL AND
CONSOLE in this Service
Information CD.
4. Ignition ON
5. Check voltage at fuel mode
switch connector LP6, circuit
39G (Pink/Blue wire).
6. Is battery voltage present?
Go to Step 3 Repair open in circuit 39G
between connector LP6
and splice joint.
Verify repair.
3. 1. Check continuity of fuel mode
switch lamp earth circuit 935C
between fuel mode switch
connector and a known good
earth.
2. Is there continuity?
Got to Step 4 Repair open in circuit
935C between connector
LP6 and splice joint.
Verify repair.
4. 1. Remove bulb and socket
assembly from fuel mode
switch, refer INSTRUMENT
FACIA AND CENTRE FACIA
ESCUTCHEON SWITCH
ILLUMINATION BULBS in
Section 12B LIGHTING
SYSTEM, of this VT Series
Service Information CD.
2. Is bulb and socket assembly
OK?
Replace fuel
mode switch,
refer 2.4 FUEL
MODE SWITCH
in Section 2B of
this Section
Replace fuel mode
switch bulb and
socket assembly.
Verify repair
3.7 ENGINE DOE S NOT CRANK
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. The LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK must be the first step when diagnosing any LPG
system problem.
2. The Theft Deterrent System must be disarmed before the engine will crank. If the Theft Deterrent System
cannot be disarmed, refer to Theft Deterrent Diagnostics in Section 12J-1, for vehicles fitted with Low Series
BCM’s or Section 12J-2 for vehicles fitted with High Series BCM’s, of this Service Information CD.
3. When PETROL is selected the engine should crank immediately the ignition switch is turned from off to start. If
the engine does not crank immediately, then refer to ON-BOARD DIAGNOSTIC SYSTEM CHECK,
Section 6C1 in this Service Information CD.
4. When LPG is selected, the engine should crank immediately the ignition Switch is turned from off to start. If the
engine cranks immediately the system is operating correctly .
5. When LPG is selected the PCM will prevent the engine from cranking if the PCM determines the throttle is
open more than approximately 5%. This tests uses TECH 2 to monitor the Throttle Position Sensor operation.
STEP ACTION YES NO
1. 1. Has LPG VEHICLE
PRELIMINARY DIAGNOSIS
CHECK been performed?
Go to step 2 Perform LPG VEHICLE
PRELIMINARY
DIAGNOSIS CHECK.
2. 1. Disarm theft deterrent system
(LED not flashing).
2. Ignition OFF.
3. Is theft deterrent system
disarmed?
Go to Step 3. Refer Section 12J-1 Low
Series BCM or
Section 12J-2 High
Series BCM in this
Service Information CD.
3. 1. Ignition ON, select Petrol via
the fuel mode switch.
2. Turn ignition switch to
“START” for a maximum of
five seconds or until engine
starts to crank.
3. Does engine crank
immediately (less than one
second)?
Go to Step 4. Refer ON-BOARD
DIAGNOSTIC
SYSTEM CHECK,
Section 6C1-2A in this
Service Information CD.
4. 1. Ignition ON, select LPG via the
fuel mode switch.
2. Turn ignition switch to
“START” for a maximum of
five seconds or until engine
starts to crank.
3. Does engine crank
immediately (less than one
second)?
System operating
correctly.
Check for
intermittent
connections.
Go to Step 5.
5. 1. Ignition OFF.
2. Install TECH 2 to DLC.
3. Ignition ON.
4. Push power button on TECH 2.
5. Select ENGINE / ENGINE
TYPE V6 LPG / Data List / All
Data.
6. Scroll to Throttle Angle.
7. Is Throttle Position Sensor
displaying 0%?
Refer ON-
BOARD
DIAGNOSTIC
SYSTEM
CHECK, Section
6C1-2A in this
Service
Information CD.
Refer Chart A-6.2
TP SENSOR
OUTPUT CHECK,
Section 6C1-2A in this
Service Information CD.
3.8 ENGINE CRANKS BUT WILL NOT START ON LPG
SHEET 1
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. The LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK must be the first step when diagnosing any LPG
system problem.
2. These initial checks are designed to verify that the engine is capable of operating on LPG.
3. Voltage is supplied to the LPG lockoff from the smart unit when the ignition is first turned on and when the
engine is cranking or running. If voltage is not present at these times the lockoff will not be energised and LPG
will not flow to the converter.
4. This test confirms correct converter operation. Incorrect converter pressures can cause the engine not to start.
5. This test determines if the ADP is causing the no start condition.
6. All hoses and vacuum lines should be checked as vacuum leaks or blockages can cause a variety of system
operating problems
7. This tests confirms correct mixer operation.
8. This tests confirms correct A DP set up.
STEP ACTION YES NO
1. 1. Has LPG VEHICLE
PRELIMINARY DIAGNOSIS
CHECK been performed?
Go to step 2. Perform LPG VEHICLE
PRELIMINARY
DIAGNOSIS CHECK.
2. INITIAL CHECKS:
1. Has LPG been selected via the
fuel mode switch?
2. Is correct LPG PROM installed
in the PCM?
3. Is the manual service valve
open?
4. Is there any LPG present in the
LPG cylinder, check contents
gauge?
If yes to all,
go to Step 3. Repair any faults.
Recheck starting
on LPG.
3. 1. Check for voltage at LPG
lockoff connector YE2 circuit
601 (Red wire).
2. Is voltage above 9 volts for 3
seconds when the ignition is
first turned on or while the
engine is cranking?
Go to Step 4. Go to Diagnostic Chart
ENGINE CRANKS BUT
WILL NOT START ON
LPG (SHEET 2) on the
following chart in this
Section.
4. 1. Test for presence of LPG in
system by checking converter
pressures. (Refer 2.15
CONVERTER in Section 2 of,
VT Sedan With Production
LPG).
2. Are converter pressures OK?
Go to Step 5. Go to Diagnostic Chart
ENGINE CRANKS BUT
WILL NOT START ON
LPG (SHEET 3) in this
Section.
5. 1. Ignition ON, select Petrol via
the fuel mode switch.
2. Start engine and bring to 2000
RPM.
3. Select the LPG mode via the
fuel mode switch.
4. Does the engine continue to
run?
Set up ADP and
adjust LPG
mixture. Refer
2.23 ADP
SET-UP
PROCEDURE in
Section 2 of,
VT Sedan With
Production LPG.
Recheck starting
on LPG.
Go to Step 6.
6. 1. Check for vacuum leaks in
vacuum or vapour feed lines
between mixer and converter,
or a blocked balance line, FCV
or Regulator Check Valve.
2. Are there any leaks or
blockages?
Repair vacuum
leaks or
blockages.
Recheck starting
on LPG.
Go to Step 7.
7. 1. Test mixer operation (refer
2.18 MIXER in Section 2 of,
VT Sedan With Production
LPG).
2. Is mixer operating correctly?
Go to Step 8. Check and repair any air
leaks between mixer and
throttle body, if no leaks
overhaul mixer. Refer
2.18 MIXER in Section 2
of, VT Sedan With
Production LPG.
Recheck starting
on LPG.
8. 1. Set up ADP and adjust LPG
mixture (refer 2.23 ADP SET-
UP PROCEDURE in Section 2
of, VT Sedan With Production
LPG) and recheck starting on
LPG.
2. Does engine start on LPG?
System OK. Go to Diagnostic Chart
ENGINE CRANKS BUT
WILL NOT START ON
LPG (2) on the following
chart in this Section.
SHEET 2
TEST DESCRIPTION
1. The smart unit and the ADP receive voltage from the LPG relay smart unit inline fuse. If this fuse is blown the
smart unit will not operate.
2. This test checks the continuity of the smart unit earth circuit. If the smart unit does not have a good earth then
it will not operate.
3. This test checks to see if the smart unit is supply ing voltage to the LPG lockoff. If voltage is present at the
smart unit then the circuit between the smart unit and the LPG lockoff is open or shorted to earth.
NOTE:
The smart unit has a current protection device on this circuit. If circuit 601 is shorted to earth the smart unit will
shutdown. The ignition must be cycled from on to off to reset the smart unit.
4. With the ignition on and LPG selected battery voltage should be supplied to circuit 905 (Pink/Green wire) when
the LPG relay is energised by the PCM.
5. This test checks if the LPG relay is operating correctly.
6. With Petrol selected via the fuel mode switch, battery voltage should be present at PCM terminal E1 circuit 935
(Pink/Black wire).
7. When LPG is selected via the fuel mode switch the PCM earths terminal E1 causing circuit 935 (Pink/Black
wire) to be pulled low, less than 0.2 volts.
8. When operating in the LPG mode, the PCM pulses the 5 volt pull up in the smart unit to earth via circuit 1 at a
50% duty cycle. Therefore the voltage at PCM terminal E5 should be 2 to 3 volts when the ignition is first turned
on or when the engine is cranking.
9. This test checks the continuity of circuit 1 (White/Green wire).
10. This test checks if circuit 1 (White/Green wire) is shorted to earth.
STEP ACTION YES NO
1. 1. Is the smart unit in line fuse
(located below the steering
column) OK?
Go to Step 2. Replace fuse. Check for
short in circuit 905.
Recheck starting
on LPG
2. 1. Check continuity of smart unit
earth circuit 151C
(Black/Yellow wire) between
smart unit connector YR50 and
a known good earth.
2. Is there continuity?
Go to step 3. Repair open in circuit 151
(Black/Yellow wire).
Recheck starting
on LPG.
3. 1. Ignition ON, LPG selected.
2. Check voltage at smart unit
connector YR50 circuit 601
(Blue/Orange wire).
3. Is voltage above 9 volts for
three seconds when the
ignition is first turned on or
while the engine is being
cranked? (REFER NOTE
ABOVE)
Repair open or
short to earth in
LPG lockoff
circuit 601
between smart
unit and lockoff.
Recheck starting
on LPG.
Go to Step 4.
4. 1. Ignition ON, LPG selected.
2. Check for voltage at smart unit
connector YR50 circuit 905
(Pink/Green wire).
3. Is battery voltage present for
three seconds when the
ignition is first turned on or
while the engine is being
cranked?
Go to Step 8. Got to Step 5.
5. 1. Is LPG relay OK.
Refer 2.3 LPG RELAY in
Section 2B of this Section for
LPG relay location.
Go to step 6. Replace LPG Relay.
Recheck starting
on LPG.
6. 1. Turn ignition ON and select
Petrol Mode via the fuel mode
switch.
2. Check voltage at PCM terminal
E1 circuit 935 (Pink/Black
wire).
3. Is battery voltage present?
Go to step 7. Repair open in circuit 935
(Pink/Black wire) between
the LPG relay and PCM.
Recheck starting
on LPG.
STEP ACTION YES NO
7. 1. Turn ignition ON and select
Petrol Mode via the fuel mode
switch.
2. Check voltage at PCM terminal
E1 circuit 935 (Pink/Black
wire).
3. Does voltage drop from battery
voltage to less than 0.2 volts
for 3 seconds when LPG is
selected via the fuel mode
switch and ignition is switched
on?
Go to step 8. Check PCM connector
terminal retention, if OK,
Replace PCM.
Recheck starting
on LPG.
8. 1. Select LPG via the fuel mode
switch.
2. Check voltage at PCM
terminal E5 circuit 1
(/White/Green wire).
3. Turn the ignition ON. Is voltage
between approx 5 volts for
three seconds when the
ignition is first turned on or
when the engine is cranking?
Check smart unit
connector
terminal
retention. If OK,
replace smart
unit.
Verify repair.
Go to step 9.
9. 1. Check continuity of circuit 1
(White/Green wire) between
smart unit connector YR50 and
PCM connector YB194
terminal E5.
2. Is there continuity?
Go to step 10. Repair open in circuit 1
(White/Green wire).
Verify repair.
10. 1. Check for a short to earth in
circuit 1 (White/Green wire)
between smart unit connector
YR50 and PCM connector
YB194 terminal E5.
2. Is there a short to earth?
Repair short to
earth in circuit 1
(White/
Green wire).
Verify repair.
Check PCM connector
terminal retention. If OK,
Replace PCM.
Recheck starting
on LPG.
SHEET 3
TEST DESCRIPTION
1. Low primary converter pressure can be caused by low supply pressure or a faulty converter.
2. If the primary converter pressure is too high the converter will have to be overhauled.
3. If the primary converter pressure is within specification but the secondary converter is out of specification, the
converter will have to be overhauled.
4. This test checks if the solenoid valve is restricting the flow of LPG.
5. This test checks the flow of LPG from the LPG cylinder to the LPG lockoff.
6. This test determines if the LPG lockoff or the converter is causing the problem.
7. This test checks if the service line is blocked. If the service line is not blocked then the manual service valve or
the LPG cylinder pick up must be blocked.
STEP ACTION YES NO
1. 1. Is primary converter pressure
below specification? Go to Step 4. Got to Step 2.
2. 1. Is primary converter pressure
above specification? Repair converter,
refer 2.15
CONVERTER in
Section 2 of,
VT Sedan With
Production LPG.
Recheck starting
on LPG.
Go to Step 3.
STEP ACTION YES NO
3. 1. If primary converter pressure is
within specification, is the
secondary converter pressure
out of specification?
Repair converter,
refer 2.15
CONVERTER
Section 2 of,
VT Sedan With
Production LPG.
Recheck starting
on LPG.
Go to step 4.
4. 1. Ignition OFF.
2. Close manual service valve.
3. Remove the solenoid valve
from the manual service valve
assembly and reinstall
solenoid sleeve, refer 2.8
SMART UNIT AND
SOLENOID VALVE in Section
2 of, VT Sedan With
Production LPG.
4. Does engine start and run on
LPG?
Replace smart
unit and solenoid
valve.
Recheck starting
on LPG.
Go to Step 5.
5. 1. Ignition OFF.
2. Close manual service valve.
3. With the solenoid valve still
removed from the manual
service valve assembly,
disconnect the front service
line at the LPG lockoff.
4. In accordance with AS-1425,
have a second technician open
the manual service valve
(slowly so that the excess flow
valve doesn’t shut LPG flow
off). If a click is heard at the
manual service valve, the
excess flow valve has closed.
5. Does LPG flow from the front
service line?
Go to Step 6. Go to Step 7.
6. 1. Test LPG lockoff (refer 2.14
LPG LOCKOFF in Section 2
of, VT Sedan With Production
LPG).
2. Is LPG lockoff OK?
Repair converter,
refer 2.14
CONVERTER in
Section 2 of,
VT Sedan With
Production LPG.
Recheck starting
on LPG.
Repair LPG lockoff, refer
2.14 LPG LOCKOFF in
Section 2 of,
VT Sedan With
Production LPG.
Recheck starting
on LPG.
7. 1. Disconnect rear service line at
manual service valve.
2. With front service line still
disconnected, blow air through
service line to check for
blockages
3. Does air flow through service
line?
Check for manual
service valve or
LPG cylinder fuel
pick-up blockage
or fault. Repair or
replace blocked
or damaged
components.
Recheck starting
on LPG.
Check for damaged or
blocked service lines.
Repair or replace blocked
or damaged components.
Recheck starting
on LPG.
3.9 ENGINE BACKFIRES ON LPG
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
NOTE:
Whenever a engine backfire has occurred the complete intake system including the mixer should be checked for
damage.
1. The LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK must be the first step when diagnosing any LPG
system problem.
2. An ON BOARD DIAGNOSTIC SYSTEM CHECK should be performed to confirm that a problem with the
Powertrain Management System is not causing the engine to backfire when operating on LPG?
3-7 An ignition system that is not operating at it’s full potential can cause an engine to backfire when operating on
LPG. Ignition leads that operate quite well when operating on petrol, can still cause problems when operating
on LPG. Therefore, all ignition system components must be at here optimum when operating on LPG.
8. Vacuum leaks or blocked vacuum lines can cause incorrect system operation, causing engine backfire.
9. An incorrect mixer operation can cause incorrect air/fuel ratios. Incorrect air/fuel ratios can cause engine
backfire.
10. An incorrect ADP set-up can cause incorrect system operation, causing engine backfire.
11. Incorrect converter operation can cause incorrect air/fuel ratios. Incorrect air/fuel ratios can cause engine
backfire.
12. This test confirm correct Regulator Check Valve (RCV) operation. Incorrect RCV operation can cause slow
converter response causing engine backfire.
13. The engine must be in optimum operating condition to prevent any possibility of the engine backfiring when
operating on LPG.
STEP ACTION YES NO
1. 1. Has LPG VEHICLE
PRELIMINARY DIAGNOSIS
CHECK been performed?
Go to step 2 Perform LPG VEHICLE
PRELIMINARY
DIAGNOSIS CHECK.
2. 1. Has an ON BOARD
DIAGNOSTIC SYSTEM
CHECK been performed?
Refer ON-BOARD
DIAGNOSTIC SYSTEM
CHECK, Section 6C-2A in this
Service Information CD.
Go to Step 3. Perform ON-BOARD
DIAGNOSTIC SYSTEM
CHECK. Refer Section
6C1-2A in this Service
Information CD.
Recheck for engine
backfire.
3. 1. Check spark plug leads for
tracking or cracks in insulation
and resistance (refer Section
6D1-3 in this Service
Information CD).
2. Are the spark plugs leads OK?
Go to Step 4. Replace spark plug leads.
Recheck for engine
backfire.
4. 1. Remove and inspect spark
plugs for fowling.
2. Are the spark plugs OK?
Go to Step 5. Replace spark plugs.
Recheck for engine
backfire.
5. 1. Re-gap spark plugs to
minimum specification.
2. Have spark plugs been re-
gaped to minimum
specification?
Go to Step 6. Re-gap spark plugs to
minimum specification
Recheck for engine
backfire.
6. 1. Check coil resistance (refer
Section 6D1-3 in this Service
Information CD).
2. Is the ignition coil resistance
within specification?
Go to Step 7. Replace faulty
ignition coil.
Recheck for engine
backfire.
7. 1. Check PCM, Direct Ignition
System (DIS) module and
Crank Angle Sensor terminal
retention.
2. Is terminal retention OK?
Go to Step 8. Resize terminals.
Recheck for engine
backfire.
STEP ACTION YES NO
8. 1. Check for vacuum leaks in
vacuum or vapour feed lines
between mixer and converter,
or a blocked balance line, FCV
or Regulator Check Valve.
2. Are there any leaks or
blockages?
Repair vacuum
leaks or
blockages.
Recheck for
engine backfire.
Go to Step 9.
9. 1. Test mixer operation (refer
2.18 MIXER in Section 2 of,
VT Sedan With Production
LPG).
2. Is mixer operating correctly?
Go to Step 10. Overhaul mixer. Refer
2.18 MIXER in Section 2
of, VT Sedan With
Production LPG.
Recheck for engine
backfire.
10. 1. Is the ADP set-up correct?
(refer 2.23 ADP SET-UP
PROCEDURE in Section 2 of,
VT Sedan With Production
LPG).
Go to Step 11. Carry out ADP set-up
procedure.
Recheck for engine
backfire.
11. 1. Test converter pressures.
(Refer 2.15 CONVERTER in
Section 2 of, VT Sedan With
Production LPG).
2. Are converter pressures OK?
Go to Step 12. Overhaul converter.
Refer 2.15 CONVERTER
in Section 2 of, VT Sedan
With Production LPG.
12. 1. Test Regulator Check Valve
operation (refer 2.16
REGULATOR CHECK VALVE
in Section 2 of, VT Sedan With
Production LPG).
2. Is Regulator Check Valve
operating correctly?
Go to Step 13. Replace Regulator Check
Valve. Refer 2.16
REGULATOR CHECK
VALVE in Section 2 of,
VT Sedan With
Production LPG.
Recheck for engine
backfire.
13. 1. Check engine mechanical
condition by checking
compression, valve timing,
intake and exhaust valves and
manifolds for casting flash.
2. Is the engine mechanical
condition OK?
Check for
incorrectly routed
harnesses,
ignition leads
or non genuine
accessories.
Repair any faults.
Recheck for engine
backfire.
3.10 POOR PERFORMANCE, FLAT SPOTTING, SLUGGISH OR POOR FUEL
CONSUMPTION WHEN OPERATING ON LPG
Because of the nature of LPG, a minimal loss of power may be experienced under heavy acceleration, this
is expected and quite normal.
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. The LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK must be the first step when diagnosing any LPG
system problem.
2. An ON BOARD DIAGNOSTIC SYSTEM CHECK should be performed to confirm that a problem with the
Powertrain Management System is not causing the engine to backfire when operating on LPG?
3. These symptoms checks this the most common causes of engine drivability problems.
4. Incorrect ADP operation can cause incorrect air/fuel ratios.
5. Incorrectly tensioned air valve to diaphragm attaching screws can cause incorrect mixer operation.
6. Correct mixer operation is required so that the correct air/fuel ratio is achieved.
7. A regulator check valve that is blocked or opening at the wrong vacuum can cause incorrect converter
operation.
8. The converter is one of the key components in the control of the delivery of LPG. Incorrect converter operation
can cause rich or lean mixtures.
STEP ACTION YES NO
1. 1. Has an LPG VEHICLE PRELIMINARY
DIAGNOSIS CHECK been
performed?
Go to step 2 Perform an LPG
VEHICLE PRELIMINARY
DIAGNOSIS CHECK.
2. 2. Has an ON BOARD DIAGNOSTIC
SYSTEM CHECK been performed?
Refer ON-BOARD DIAGNOSTIC
SYSTEM CHECK, Section 6C1-2A in
this Service Information CD.
Go to Step 3. Perform ON-BOARD
DIAGNOSTIC SYSTEM
CHECK. Refer Section
6C1-2A in this Service
Information CD.
Recheck performance.
3. 1. Carry out SYMPTOMS CHECK (refer
Section,
6C1-2B in this Service Information
CD).
2. Are all checks OK?
Go to Step 4. Repair any faults.
Recheck performance.
4. 1. Is the ADP set-up correctly?
(refer 2.23 ADP SET-UP
PROCEDURE in Section 2 of,
VT Sedan With Production LPG).
Go to Step 5. Carry out ADP set-up
procedure.
Recheck performance.
5. 1. Check air valve to diaphragm
attaching screws for correct torque.
(refer 2.18 MIXER in Section 2 of , VT
Sedan With Production LPG).
2. Are screws tightened to the correct
torque?
Go to Step 6. Tension Screws to the
correct torque
specification, refer 2.18
MIXER in Section 2 of,
VT Sedan With
Production LPG.
Recheck performance.
6. 1. Test mixer operation (refer 2.18
MIXER in Section 2 of,
VT Sedan With Production LPG).
2. Is mixer operating correctly?
Go to Step 7. Overhaul mixer. Refer
2.18 MIXER in Section 2
of, VT Sedan With
Production LPG.
Recheck performance.
7. 1. Test Regulator Check Valve operation
(refer 2.16 REGULATOR CHECK
VALVE in Section 2 of, VT Sedan With
Production LPG).
2. Is Regulator Check Valve operating
correctly?
Go to Step 8. Replace Regulator
Check Valve.
Recheck performance.
8. 1. Test converter operation (refer 2.16
CONVERTER in Section 2 of, VT
Sedan With Production LPG).
2. Is converter operating correctly?
System OK Repair converter, refer
2.16 CONVERTER in
Section 2 of, VT Sedan
With Production LPG.
Recheck performance.
3.11 FUEL CONTROL VALVE DOES NOT OPERATE
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. The LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK must be the first step when diagnosing any LPG
system problem.
2. These initial checks are designed to verify that the engine is capable of operating on LPG.
3. If the FCV can be heard operating the ADP is being powered up and pulsing the FCV.
4. This test checks that the ADP is pulsing the FCV.
5. This test checks if power is being supplied to the FCV.
6. This test checks if the ADP is supplying power to circuit 107 (Yellow wire).
7. This test checks the continuity of circuit 105 Yellow/Black wire.
8. This test checks that battery voltage is being supplied from the LPG relay to the ADP via circuit 905
(Pink/Green wire).
9. This test checks the continuity of both of the ADP earth circuits.
10. In this test step, circuit 105 (Yellow/Black wire) is checked for a short to earth?
11. This test checks the operation of the FCV.
STEP ACTION YES NO
1. 1. Has LPG VEHICLE
PRELIMINARY DIAGNOSIS
CHECK been performed.
Go to step 2. Perform LPG VEHICLE
PRELIMINARY
DIAGNOSIS CHECK.
2. INITIAL CHECKS:
1. Has LPG been selected via the
fuel mode switch?
2. Is correct LPG PROM installed
in the PCM?
3. Is smart unit in line fuse
(located under steering
column) OK?
If YES to all,
go to Step 3. Repair any faults.
Verify repair.
3. 1. Ignition ON, LPG selected via
fuel mode switch.
2. Can fuel control valve be heard
operating for three seconds
when ignition first switched on?
Go to Step 10. Go to step 4
4. 1. Remove connectors from FCV.
2. Ignition ON.
3. Check voltage between FCV
circuits 107 (Yellow wire) and
105 (Yellow/Black wire).
4. Is voltage at least 9 volts for
three seconds when ignition
first switched on?
Go to step 10. Go to Step 5.
5. 1. Remove connectors from FCV
terminals.
2. Ignition ON, LPG selected via
fuel mode switch.
3. Check for voltage between
FCV connector YE2 circuit 107
(Yellow wire) and a known
good earth.
4. Is battery voltage present for
three seconds when ignition
first switched on?
Go to Step 7. Go to Step 6.
STEP ACTION YES NO
6. 1. Ignition ON, LPG selected via
fuel mode switch.
2. Check for voltage at ADP
connector LP4 circuit 107
(Yellow wire).
3. Is battery voltage present for
three seconds when ignition is
first switched on?
Repair circuit 107
(Yellow wire).
Verify repair.
Go to Step 7.
7. 1. Check continuity of circuit 105
(Yellow/Black wire) between
FCV terminal YE2 and ADP
connector LP4.
2. Is there continuity?
Go to Step 8. Repair open in circuit 105
(Yellow/Black wire)
Verify repair.
8. 1. Ignition ON, LPG selected via
fuel mode switch.
2. Check for voltage at ADP
connector LP4 circuit 905
(Pink/Green wire).
3. Is battery voltage present for
three seconds when ignition
first switched on?
Go to Step 9. Repair open circuit 905
(Pink/Green wire).
Verify repair.
9. 1. Check continuity of ADP earth
circuits 151 (Black /Yellow
wire) and circuit 3 (Black/Red
wire) from ADP connector LP4
and a known good earth.
2. Is there continuity?
Check ADP
connector
terminal retention
if OK, replace
ADP.
Verify repair.
Repair faulty ADP
earth circuit 151
(Black/Yellow w ire)
and 3 Black/Red Wire.
Verify repair.
10. 1. Check for a short to earth in
circuit 105 (Yellow/Black wire).
2. Is circuit 105 (Yellow/Black
wire) shorted to earth?
Repair short to
earth in circuit
105 (Yellow/
Black wire). Verify
repair.
Go to step 11.
11. 1. Test operation of FCV, (refer
2.17 FUEL CONTROL
VALVES in Section 2 of,
VT Sedan With Production
LPG).
2. If FCV operating correctly?
Perform ADP set
up procedure.
Refer 2.23
ADAPTIVE
DIGITAL
PROCESSOR
SET-UP
PROCEDURE in
Section 2 of,
VT Sedan With
Production LPG.
Verify repair.
Check FCV connector
terminal retention if OK,
replace FCV.
Verify repair.
3.12 FUEL GAUGE DOES NOT OPERATE
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. The LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK must be the first step when diagnosing any LPG
system problem.
2. In this test TECH 2 is used to test the operation of the instrument cluster fuel gauge.
3. This test confirms correct operation of the cylinder fuel gauge assembly.
4. If the TECH 2 instrument LPG sender signal is displaying 5 volts, the LPG sender circuit is open circuited.
5. If the TECH 2 instrument LPG sender signal is displaying 0 volts, the LPG sender circuit is short circuited.
6. This test step checks the continuity of the cylinder fuel gauge earth circuit.
7. In this test step, circuit 5 (Yellow wire) is checked for a short to earth.
8. This test step checks the continuity of the LPG sender earth circuit 5.
9. This test checks for continuity on circuit 5, between LPG body harness connector YR50 and instrument cluster
assembly connector YB66.
10. In this test step, the cylinder fuel gauge assembly is removed from the LPG cylinder and checked for correct
operation.
CAUTION:
All safety precautions listed in 2.12 CYLINDER FUEL GAUGE ASSEMBLY in Section 2 of, VT Sedan With
Production LPG must be observed.
DIAGNOSTIC AIDS
On VT Series Models built before L326280 (Executive) and L327258 (Berlina), fitted with accessory LPG systems, it
was a requirement to replace the instrument cluster assembly to obtain interface capabilities with the LPG system
(for additional information, refer to Holden Newsline NL156 (15/4/98)).
Instrument clusters with LPG interface capabilities can be identified by a sticker on the housing; labelled “EE
Version 15” or latter (ie. EE 15, EE 16, EE 17, etc.).
STEP ACTION YES NO
1. 1. Has LPG VEHICLE
PRELIMINARY DIAGNOSIS
CHECK been performed?
Go to step 2 Perform LPG VEHICLE
PRELIMINARY
DIAGNOSIS CHECK.
2. 1. Install TECH 2 to DLC.
2. Select Body / Instruments /
Miscellaneous Tests / Control
Tests / Fuel Gauge Level
3. Run Fuel Gauge Level test.
4. Does fuel gauge operate
correctly?
Go to Step 3. Replace instrument
cluster, refer to Section
12C INSTRUMENTS,
WIPERS / WASHERS
AND HORNS in this
Service Information CD
3. 1. Does fuel gauge operate when
petrol is selected via the fuel
mode switch?
Go to step 4. Refer 3.13 FUEL GAUGE
DOES NOT OPERATE
WHEN PETROL
SELECTED in this
Section.
4. 1. Test operation of cylinder fuel
gauge. (refer 2.12 CYLINDER
FUEL GAUGE ASSEMBLY in
Section 2 of, VT Sedan With
Production LPG).
2. Is cylinder fuel gauge
operating correctly?
Go to step 5. Replace cylinder fuel
gauge. (refer 2.12
CYLINDER FUEL
GAUGE ASSEMBLY in
Section 2 of, VT Sedan
With Production LPG).
5. 1. Install TECH 2 to DLC and
select Body/ Instruments /
Data Display / Instrument.
2. Scroll to LPG Sender Signal.
3. Is the LPG Sensor Signal 5
Volts.
Go to step 7. Go to step 6.
STEP ACTION YES NO
6. 1. In test step 5, is the LPG
Sender Signal 0 Volts? Go to step 7. Go to step 10.
7. 1. Check circuit 5 (Yellow wire)
for short to earth.
2. Is circuit 5 (Yellow wire)
shorted to earth?
Repair short to
earth in circuit 5
(Yellow wire).
Verify Repair.
Go to step 10.
8. 1. Check continuity of earth
circuit 3, (Black/Red wire)
between LPG body harness
connector YR50 and earth.
2. Is there continuity?
Go to step 9. Repair open in earth
circuit 3 (Black/Red wire).
Verify repair.
9. 1. Check continuity of circuit 5,
(Yellow wire) between LPG
body harness connector YR50
and instrument cluster
assembly connector YB66.
2. Is there continuity?
Go to step 10. Repair open in circuit 5
(Yellow wire).
Verify repair.
10. 1. Remove cylinder fuel gauge
assembly, refer 2.12
CYLINDER FUEL GAUGE
ASSEMBLY in Section 2 of,
VT Sedan With Production
LPG.
2. Check operation of cylinder
fuel gauge assembly.
3. Check for binding, jammed &
smooth operation).
4. Does cylinder fuel gauge asm.
operate correctly?
Check all
connector
terminal
retention. Monitor
TECH 2
Instrument Data
List while
manipulating
wiring harness to
check for an
intermittent
connection.
Replace cylinder fuel
gauge assembly, refer
2.12 CYLINDER FUEL
GAUGE ASSEMBLY in
Section 2 of, VT Sedan
With Production LPG.
Verify repair.
3.13 FUEL GAUGE DOES NOT OPERATE WHEN PETROL SELECTED
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. The LPG VEHICLE PRELIMINARY DIAGNOSIS CHECK must be the first step when diagnosing any LPG
system problem.
2. In this test, TECH 2 is used to check the signal from the fuel gauge sender.
3. In this test, TECH 2 is used to check circuit 30 (Tan wire), if the fuel gauge sender unit signal is not 0 volts
circuit 30 is open.
4. In this test, TECH 2 is used to check circuit 30 (Tan wire), if the fuel gauge sender unit signal is not 5 volts
circuit 30 is shorted to earth.
5. In this test step, circuit 155 (Black/Yellow wire) is checked for open circuit.
6. This test confirms correct fuel gauge sender unit operation.
DIAGNOSTIC AIDS
On VT Series Models built before L326280 (executive) and L327258 (Berlina), fitted with accessory LPG systems, it
was a requirement to replace the instrument cluster assembly to obtain full interface capabilities with the LPG
system (for additional information, refer to Holden Newsline NL156 (15/4/98)).
Instrument clusters with full LPG interface capabilities can be identified by a sticker on the housing; labelled “EE
Version 15” or latter (ie. ‘EE 15’, ‘EE 16’, ‘EE 17’, etc.).
STEP ACTION YES NO
1. 1. Has LPG VEHICLE PRELIMINARY
DIAGNOSIS CHECK been
performed?
Go to step 2 Perform LPG VEHICLE
PRELIMINARY
DIAGNOSIS CHECK.
2. 1. Install TECH 2 to DLC.
2. Select Body/ Instruments / Data
Display / Instrument.
3. Scroll to Fuel Gauge Sender Signal.
4. Is the Fuel Gauge Sensor Signal 5
Volts?
Go to step 3. Go to step 4.
3. 1. With TECH 2 connected to DLC.
2. Disconnect fuel gauge sender unit
connector YR44.
3. Jumper circuit 30 (Tan wire) to a
known good earth.
4. Is the Fuel Gauge Sensor Signal 0
Volts?
Go to step 6. Repair open in circuit 30
(Tan wire).
Verify repair.
4. 1. With TECH 2 connected to DLC.
2. Disconnect fuel tank connector YR44.
3. Is the Fuel Gauge Sensor Signal 5
Volts?
Go to step 5. Repair short to earth in
circuit 30 (Tan wire).
Verify repair.
5. 1. Disconnect fuel gauge sender unit
connector YR44.
2. Check continuity of fuel gauge sender
unit earth circuit 155 (Black/Yellow
wire) between fuel tank connector
YR44 and a known good earth.
3. Is there continuity?
Go to step 6. Repair open in earth
circuit 155
(Black/Yell ow wire).
Verify repair.
6. 1. Test operation of fuel gauge sender
unit. (refer 2.3 SENDER UNIT in
Section 12C ).
2. Is fuel gauge sender unit operating
correctly?
Check all
connector
terminal
retention.
Monitor TECH 2
Instrument Data
List while
manipulating
wiring harness to
check for an
intermittent
connection.
Replace fuel gauge
sender unit.
(Refer 2.3 FUEL
SENDER ASSEMBLY
in Section 8A ).
