Operation Section
78
Table 2. Diagnostic Fault Codes (Flash Codes) cont’d.
DFC
PROBABLE FAULT
FAULT ACTION *
CORRECTIVE ACTION FIRST CHECK
772
GasPostO2FailedRich
Pre-catalyst O2 sensor
indicates extended rich
operation on LPG
(1) TurnOnMil
(2) DisableGasPost
O2Ctrl
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
LiqFuelAdaptRangeLo
w
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
Ω
± 0.4
Ω
)
O2 Pin 2 (HEATER GND) to Pin 1 (HEATER
PWR)
842
LiqPostO2NotActive
Post-catalyst O2 sensor
inactive on gasoline,
open O2 sensor signal or
heater leads, defective
O2 sensor.
(1) TurnOnMil
(2) DisableLiqPost
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
Ω
± 0.4
Ω
)
O2 Pin 2 (HEATER GND) to Pin 1 (HEATER
PWR)
851
LiqO2FailedLean
Pre-catalyst O2 sensor
indicates extended lean
operation on gasoline
(1) TurnOnMil
(2) DisableLiquid
O2Ctrl
Check for vacuum leaks.
Low gasoline fuel pressure, perform gasoline
pressure test.
Injector problems, e.g. plugged, defective
injector
(*) Fault actions shown are default values specified by the OEM.