P0148

DTC P0148

CIRCUIT DESCRIPTION
The powertrain control module (PCM) opens the AF enable circuit when operating on compressed natural gas (CNG). When the AF enable circuit is open the fuel injector control module (FICM) operates the CNG injectors based upon the PCM fuel injector control pulse width signals. The PCM grounds 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.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0148 Incorrect Fuel Mode

CONDITIONS FOR RUNNING THE DTC
- The ignition voltage is between 6-8 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 lamp (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.

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

Step 1 - Step 11:

Step 12 - Step 13:

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the condition is active.
4. This step tests for a short to ground on the AF enable circuit.