SECTION 3A - DIAGNOSIS - VT WAGON
3. GENERAL INFORM ATION
Excluding the diagnostic procedures published in this Section, LPG system diagnosis procedures for VT Wagon
Models carr y over from those detailed in Section 3 DIAGNOSIS, under VT Sedan With Production LPG, in the VT
Series Service Information CD, noting the following:
1. Connector YR50 is only applicable to VT Sedan Models. O n VT Wagon Models, the LPG tank connec tor YR51
is used in lieu of YR50, refer to wiring diagrams in Section 12P WIRING DIAGRAMS.
2. If a diagnostic procedure requests the smart unit and solenoid valve be removed, refer to
2.8 SMART UNIT AND SOLENOID VALVE in Section 2A.
3. If a diagnostic procedure requests the fuel gauge assembly be removed, refer to 2.12 TANK FUEL GAUGE in
Section 2A.
NOTE:
Due to a change to the PCM PROM sof tware at the start of VT LPG produc tion (but af ter publication of Volume 9)
some diagnostic procedures published in the VT Series Service Information CD may lead to incorrect diagnosis.
The change to the PROM software resulted in the LPG relay being switched OFF after 3 seconds of the ignition
being switched ON (the LPG relay remains switched ON if the engine is running or being cranked).
As a result of this, the following diagnostic procedures have been r epublished to reflec t the corr ect operation of the
LPG system and can be used on VT Wagon and Sedan Models with production fitted LPG systems.
Techline
3.1 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. Vacuum leaks or blockages can cause a variety of system operating problems. All hoses and vacuum lines
should be checked.
7. This test confirms correct mixer operation.
8. This test confirms correct A DP set up.
Techline
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,
refer Section 3 in
VT Sedan With
Production LPG.
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 965 (Blue/Yellow
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 (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 (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
The numbers below refer to step numbers in the following diagnostic chart.
1. The smart unit and the ADP receive voltage from the LPG relay via fuse F9. If fuse F9 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 supplying 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 965 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 1035 (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
(Red/Yellow wire).
7. When LPG is selected via the fuel mode switch the PCM earths terminal E1 causing circuit E1 circuit 935
(Red/Yellow 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 937 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 check the continuity of circuit 937(White/Green wire).
10. This test checks if circuit 937(White/Green wire) is shorted to earth.
STEP ACTION YES NO
1. 1. Is fuse F9 OK? Go to Step 2. Replace fuse.
Check for short in LPG
lockoff circuit 965.
Recheck starting
on LPG
2. 1. Check continuity of smart unit
earth circuit 750 (Black/Red
wire) between smart unit
connector YR51 and a known
good earth.
2. Is there continuity?
Go to step 3. Repair open in circuit 750
(Black/Red wire).
Recheck starting
on LPG.
3. 1. Ignition ON, LPG selected.
2. Check voltage at smart unit
connector YR51 circuit 965
(Blue/Red wire).
3. Is voltage above 9 volts for
three seconds when the
ignition is first turned on or
while the engine is being
cranked?
Repair open or
short to earth in
LPG lockoff
circuit 965
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 YR51 circuit 1035
(Pink/Green wire).
3. Is battery voltage present for
three seconds when the
ignition is first turned on or
while engine is being cranked?
Go to Step 8. Got to Step 5.
5. 1. Is LPG relay OK.
Refer 2.21 in Section 2, of
VT Sedan With Production
LPG, for LPG relay location.
Go to step 6. Replace LPG Relay.
Recheck starting
on LPG.
6. 1. Ignition ON, select Petrol Mode
via the fuel mode switch.
2. Check voltage at PCM terminal
E1 circuit 935 (Red/Yellow
wire).
3. Is battery voltage present?
Go to step 7. Repair open in circuit 935
(Red/Yellow wire)
between the LPG
relay and PCM.
Recheck starting
on LPG.
STEP ACTION YES NO
7. 1. Ignition ON, Petrol Mode
selected via the fuel mode
switch.
2. Check voltage at PCM terminal
E1 circuit 935 (Red/Yellow
wire).
3. Does voltage drop from battery
voltage to less than 0.2 volts
for three seconds when LPG is
selected via the fuel mode
switch?
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 937 (White/Green
wire).
3. Turn the ignition on, is voltage
approximately 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 937
(White/Green wire) between
smart unit connector YR51 and
PCM connector YB194
terminal E5.
2. Is there continuity?
Go to step 10. Repair open in circuit 937
(White/Green wire).
Verify repair.
10. 1. Check for a short to earth in
circuit 937 (White/Green wire)
between smart unit connector
YR51 and PCM connector
YB194 terminal E5.
2. Is there a short to earth?
Repair short to
earth in circuit
937 (White/
Green wire).
Verify repair.
Check PCM connector
terminal retention, if OK,
Replace PCM.
Recheck starting
on LPG.
SHEET 3
TEST DESCRIPTION
The numbers below refer to step numbers in the following diagnostic chart.
1. Low primary converter pressure can be cause 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. Go 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.
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 (Sedan) or
Section 2A, in this Section
(Wagon).
4. Does engine start and run on
LPG?
Replace smart
unit and
solenoid valve.
Recheck starting
on LPG.
Go to Step 5.
STEP ACTION YES NO
5. 1. Ignition OFF.
2. Close manual service valve.
3. With the solenoid valve still
removed from the manual
service valve assembly.
4. Disconnect the front service
line at the LPG lockoff.
5. 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 herd at the
manual service valve, the
excess flow valve has closed).
6. 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.
3.2 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 1061 (Blue/Yellow wire).
7. This test checks the continuity of circuit 1062 Green wire.
8. This test checks that battery voltage is being supplied from the LPG relay to the ADP via circuit 1035
(Pink/Blue wire).
9. This test checks the continuity of both of the ADP earth circuits.
10. In this test step circuit 1062 (Green wire) is checked for a short to earth?
11. This test checks the operation of the FCV.
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,
refer Section 3 of
VT Sedan With
Production LPG.
2. INITIAL CHECKS:
1. Has LPG been selected via
the fuel mode switch?
2. Is correct LPG PROM installed
in the PCM?
3. Is fuse F9 OK?
If YES to all, go to
Step 3. Repair any faults.
Verify repair.
3. 1. Ignition ON, select LPG via
fuel mode switch.
2. Can fuel control valve be
heard operating for three
seconds when ignition
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 1061 (Blue/Yellow
wire) and 1062 (Black/Blue
wire).
4. Is voltage at least 9 volts for
three seconds when ignition
switched on?
Go to step 10. Go to Step 5.
5. 1. Remove connectors from FCV
terminals.
2. Ignition ON, select LPG via
fuel mode switch.
3. Check for voltage between
connector YE2 circuit 1061
(Blue/Yellow wire) and a
known good earth.
4. Is battery voltage present for
three seconds when ignition
switched on?
Go to Step 7. Go to Step 6.
STEP ACTION YES NO
6. 1. Ignition ON, select LPG via
fuel mode switch.
2. Check for voltage at ADP
connector YB122 circuit 1061
(Blue/Yell ow wire).
3. Is battery voltage present for
three seconds when ignition
switched on?
Repair circuit
1061 (Blue/
Yellow wire).
Verify repair.
Go to Step 7.
7. 1. Check continuity of circuit
1062 (Black/Blue wire)
between FCV terminal YE2
and ADP connector YB122.
2. Is there continuity?
Go to Step 8. Repair open in circuit
1062 (Black/Blue wire)
Verify repair.
8. 1. Ignition ON, and LPG selected
via fuel mode switch.
2. Check for voltage at ADP
connector YB122 circuit 1035
(Pink/Blue wire).
3. Is battery voltage present for
three seconds when ignition
switched on?
Go to Step 9. Repair open circuit 1035
(Pink/Blue wire).
Verify repair.
9. 1. Check continuity of ADP earth
circuits 750 (Black/ Red wire)
and circuit 751 (Black/Blue
wire) from ADP connector
YB122 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 750 (Black/Red
wire) and 751
Black/Blue Wire.
Verify repair.
10. 1. Check for short to earth in
circuit 1062 (Green wire).
2. Is circuit 1062 (Black/Blue
wire) shorted to earth?
Repair short to
earth in circuit
1062 (Black/
Blue wire).
Verify repair.
Go to step 11.
11. 3. Test operation of FCV, (refer
2.17 FUEL CONTROL
VALVES in Section 2, of VT
Sedan With Production LPG).
4. If FCV operating correctly?
Perform ADP set
up procedure.
(refer 2.23 FUEL
CONTROL
VALVES in
Section 2, of
VT Sedan With
Production LPG).
Verify repair.
Check FCV connector
terminal retention if OK,
replace FCV.
Verify repair.