Note. To locate components, see COMPONENT LOCATIONS . For circuit reference, see WIRING DIAGRAMS . For connector terminal identification, see CONNECTOR IDENTIFICATION . If an intermittent condition exists, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.
Note. For removal and installation of Bi-Fuel and CNG related components, see REMOVAL & INSTALLATION - SIERRA & SILVERADO - BI-FUEL & CNG article. For removal and installation of gasoline related components, see REMOVAL & INSTALLATION - SIERRA & SILVERADO - FLEX-FUEL & GASOLINE article.
Circuit Description
The Powertrain Control Module (PCM) grounds the Alternative Fuel (AF) enable circuit when operating on CNG. When the AF enable circuit is grounded the Fuel Injector Control Module (FICM) operates the CNG injectors based upon the PCM fuel injector control pulse width signals. On Bi-Fuel (KL6) vehicles the PCM opens the AF enable circuit when gasoline operation is desired. Switch-over from one fuel to the other is always performed in an orderly, sequential manner. Since some injectors are in the middle of injecting the previous fuel, the FICM will wait until that cylinders fuel delivery is complete and will then switch over in sequential firing order.
Conditions For Running The DTC
- The ignition voltage is 6-18 volts.
- The engine is cranking, or running.
Conditions For Setting The DTC
- The PCM detects that the commanded state and the actual state of the AF enable circuit do not match.
- The condition exists for at least 2 seconds.
Action Taken When The DTC Sets
- The control module illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.