Circuit Description
The powertrain control module (PCM) grounds the AF Enable circuit when operating on CNG. When the AF Enable circuit is grounded the AF relay is energized. The AF relay supplies power to all of the AF injector relays. The switched AF relay voltage also signals the fuel injector control module (FICM) to operate the CNG injectors based upon the PCM fuel injector control pulse width signals. 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. The PCM controls the AF enable circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the controlled component. The PCM monitors the status of the driver. If the PCM detects an incorrect voltage for the commanded state of the driver, DTC P2146 sets.
Conditions for Running the DTC
The ignition voltage is more than 6 volts.
Conditions for Setting the DTC
| • | The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match. |
| • | The above condition exists for at least 1 seconds. |
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.
-
This step tests if the concern is active.
-
This step tests the AF enable circuit to the AF relay. If the test lamp turns ON and OFF, with the scan tool commands, the PCM and wiring are OK.
-
This step determines if a ground is constantly applied to the AF enable circuit.
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This step verifies that a voltage is supplied to the AF relay. If the ignition voltage circuit is open, this DTC will set.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views | |||
1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
Does DTC P2146 set? | Go to Step 4 | Go to Step 3 | |
3 |
Did the DTC fail this ignition? | Go to Step 4 | Go to Intermittent Conditions |
Does the test lamp respond to the scan tool commands? | Go to Step 8 | Go to Step 5 | |
Does the test lamp remain illuminated? | Go to Step 7 | Go to Step 6 | |
6 | Test the AF enable output circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the J Platform Service Manual. Did you find and correct the condition? | Go to Step 14 | Go to Step 10 |
7 | Test the AF enable output circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the J Platform Service Manual. Did you find and correct the condition? | Go to Step 14 | Go to Step 13 |
Probe the AF relay ignition voltage circuit with a test lamp connected to a good ground. Does the test lamp illuminate? | Go to Step 9 | Go to Step 11 | |
9 | Inspect for poor connections at the harness connector of the AF relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the J Platform Service Manual. Did you find and correct the condition? | Go to Step 14 | Go to Step 12 |
10 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the J Platform Service Manual. Did you find and correct the condition? | Go to Step 14 | Go to Step 13 |
11 | Repair the ignition voltage circuit of the AF relay for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the J Platform Service Manual. Did you complete the repair? | Go to Step 14 | -- |
12 | Replace the AF relay. Did you complete the replacement? | Go to Step 14 | -- |
13 | Replace the PCM. Refer to Powertrain Control Module Replacement in the J Platform Service Manual. Did you complete the replacement? | Go to Step 14 | -- |
14 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 15 |
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |
