GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Chevy C Silverado - 2WD (CNG) 🢒 Engine 🢒 Engine Controls - 6.0L 🢒 DTC P2146

Circuit Description

The powertrain control module (PCM) opens the AF enable circuit in order to operate on CNG. When the AF enable circuit is open the AF fuel mode relay switch is open. The PCM fuel injector pulse width modulated (PWM) signals are routed through the AF injector relays to the fuel injector control module (FICM). The FICM will operate the CNG injectors based upon the PCM pulse width signals. When gasoline operation is desired, the PCM grounds the AF enable circuit. When the AF enable circuit is grounded the AF fuel mode relay closes. The AF fuel mode relay provides a ground path for all of the AF injector relays. The PCM fuel injector pulse width modulated (PWM) signals are routed through the AF injector relays to the gasoline fuel injectors. 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 between 6 and 18 volts.
    • The engine speed is more than 400 RPM.

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 second.

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

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

  1. This step tests if the concern is active.

    2.

  2. This step determines if the PCM is receiving 12 volts from the AF fuel mode relay.

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)

2

  1. Turn ON the ignition, with the engine OFF.
  2. Clear the DTC information with a scan tool.
  3. Start and idle the engine.
  4. Observe the DTC information with a scan tool.

Does DTC P2146 set?

Go to Step 3

Go to Step 4

3

Is DTC P0148 also set?

Go to DTC P0148

Go to Step 5

4
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30  seconds.
  3. Turn ON the ignition, with the engine OFF.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 5

Go to Intermittent Conditions

5

  1. Disconnect the PCM. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.
  2. Probe the AF enable circuit with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 7

6

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 G Van Service Manual.

Did you find and correct the condition?

Go to Step 9

Go to Step 8

7

Repair the open in the AF enable circuit between the PCM and the splice.

Did you complete the repair?

Go to Step 9

--

8

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.

Did you complete the replacement?

Go to Step 9

--

9
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30  seconds.
  3. Turn ON the ignition, with the engine OFF.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 10

10

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK