Service manual

G420F(FE) Service Manual Chapter 9. Advanced Diagnostics 303
Table 2. Diagnostic Fault Codes (Flash Codes) cont’d.
DFC PROBABLE FAULT FAULT ACTION *
CORRECTIVE ACTION
FIRST CHECK
771
(77)
GasO2FailedRich
Pre-catalyst O2 sensor
indicates extended rich
operation on LPG
(1) TurnOnMil
(2) DisableGas O2Ctrl
Check fuel trim valves, e.g. plugged
valve or hose.
Check for plugged orifice(s).
772
GasPostO2FailedRich
Pre-catalyst O2 sensor
indicates extended rich
operation on LPG
(1) TurnOnMil
(2) DisableGasPostO2Ctrl
Correct other faults that may
contribute to 772 (e.g. faults pertaining
to FTVs, Pre-Cat O2, Post Cat O2
sensor)
Look for leaks in exhaust, catalytic
converter, HEGO sensors; repair
leaks.
Check all sensor connections (see
fault 742 corrective actions).
821
LiqFuelAdaptRangeHi
In Gasoline mode, system
had to adapt lean more
than expected
TurnOnMil
Check for vacuum leaks. Low gasoline
fuel pressure, perform gasoline
pressure test. Injector problems, e.g.
plugged, defective injector.
831
LiqFuelAdaptRangeLow
In Gasoline mode, system
had to adapt rich more
than expected
TurnOnMil
Low gasoline fuel pressure, perform
gasoline pressure test Injector
problems, e.g. leaking, defective
injector.
841
LiqO2NotActive
Pre-catalyst O2 sensor
inactive on gasoline, open
O2 sensor signal or
heater leads, defective
O2 sensor
(1) TurnOnMil
(2) DisableLiquid 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)
(*) Fault actions shown are default values specified by the OEM.