Service manual

G420F(FE) Service Manual Chapter 9. Advanced Diagnostics 302
Table 2. Diagnostic Fault Codes (Flash Codes) cont’d.
DFC PROBABLE FAULT FAULT ACTION *
CORRECTIVE ACTION
FIRST CHECK
731
(73)
GasFuelAdaptRangeHi
In LPG mode, system had
to adapt lean more than
expected
TurnOnMil
Check fuel trim valves, e.g. plugged
valve or hose. Check for plugged
orifice(s).
741
(74)
GasO2NotActive
Pre-catalyst O2 sensor
inactive on LPG, open O2
sensor signal or heater
leads, defective O2
sensor
(1) TurnOnMil
(2) DisableGas O2Ctrl
Check that Pre-catalyst O2 sensor
connections are OK.
O2 (signal) Pin 3 to SECM Pin B13 O2
Pin 2 (HEATER GND) to SECM
(DRVG GNG)
Pins A16, B17 O2 Pin 1 (HEATER
PWR) to SECM (DRVP + 12V) Pin A23
Verify O2 sensor heater circuit is
operating by measuring heater
resistance (2.1  ± 0.4 ) O2 Pin 2
(HEATER GND) to Pin 1 (HEATER
PWR)
742
GasPostO2NotActive
Post-catalyst O2 sensor
inactive on LPG, open O2
sensor signal or heater
leads, defective O2
sensor.
(1) TurnOnMil
(2) DisableGasPost O2Ctrl
Check that Post-catalyst O2 sensor
connections are OK.
O2 (signal) Pin 3 to SECM Pin B19
O2 Pin 2 (HEATER GND) to SECM
(DRVG GNG) Pins A16, B17
O2 Pin 1 (HEATER PWR) to Post O2
Heater Relay. Relay pin 87. This relay
only turns on after engine has been
running for some time and SECM has
calculated that water condensation in
exhaust has been removed by exhaust
heat. Post O2 Heater Relay has SECM
(DRVP + 12V) applied to the relay coil
power. The relay coil ground is
controlled by SECM Pin A20 to activate
the relay to flow current through the
post O2 heater.
Verify O2 sensor heater circuit is
operating by measuring heater
resistance (2.1  ± 0.4 )
O2 Pin 2 (HEATER GND) to Pin 1
(HEATER PWR)
743 Reserved
751
GasO2FailedLean
Pre-catalyst O2 sensor
indicates extended lean
operation on LPG
(1) TurnOnMil
(2) DisableGas O2Ctrl
Check for vacuum leaks. Check fuel
trim valves, e.g. leaking valve or hose.
Check for missing orifice(s).
752
GasPostO2FailedLean
Pre-catalyst O2 sensor
indicates extended lean
operation on LPG
(1) TurnOnMil
(2) DisableGasPost O2Ctrl
Correct other faults that may contribute
to 752 (e.g. faults pertaining to dither
valves, Pre-Cat O2, Post Cat O2
sensor)
Check for vacuum leaks Check for
leaks in exhaust, catalytic converter,
HEGO sensors; repair leaks. Check all
sensor connections (see fault 742
corrective actions).