Operation Section Table 2. Diagnostic Fault Codes (Flash Codes) cont’d. (*) Fault actions shown are default values specified by the OEM. 78 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 (2.1Ω ± 0.4Ω) 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 (2.1Ω ± 0.4Ω) 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