P0148

DTC P0148

Circuit Description

The powertrain control module (PCM) grounds the 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 is ON.

Conditions for Setting the DTC

The PCM detects that the commanded state and the actual state of the AF Enable circuit do not match.

Action Taken When the DTC Sets

- The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The control module switches over to gasoline fuel operation.
- The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2. This step determines if the condition is active. The PCM grounds the AF Enable circuit when operating on CNG.
4. This step tests for a short to ground on the AF Enable circuit. The test lamp should not illuminate with the ignition OFF.