Operation Section Table 2. Diagnostic Fault Codes (Flash Codes) cont’d. (*) Fault actions shown are default values specified by the OEM. 77 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 dual dither 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 (2.1Ω ± 0.4Ω) 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 (2.1Ω ± 0.4Ω) O2 Pin 2 (HEATER GND) to Pin 1 (HEATER PWR) 751 GasO2FailedLean Pre-catalyst O2 sensor indicates extended lean operation on LPG (1) TurnOnMil (2) DisableGas O2Ctrl Check for vacuum leaks. Check dual dither 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). 771 (77) GasO2FailedRich Pre-catalyst O2 sensor indicates extended rich operation on LPG (1) TurnOnMil (2) DisableGas O2Ctrl Check dual dither valves, e.g. plugged valve or hose. Check for plugged orifice(s).