GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Express (CNG) 🢒 DTC 🢒 DTC P2146

Circuit Description

The powertrain control module (PCM) grounds the AFO enable circuit when operating on CNG. When the AFO enable circuit is grounded the fuel injector control module (FICM) will operate the CNG injectors based upon the PCM pulse width signals. The PCM controls alternative fuel operation by grounding the AFO 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 is ON.

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) 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 tests if a ground is constantly being applied to the AFO enable circuit. With the FICM disconnected, the PCM will command gasoline operation. The AFO enable circuit should not illuminate the test lamp.

    3.

  3. This step verifies that the PCM is providing ground to the AFO enable circuit.

Step

Action

Value(s)

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

Important: If DTC P0611 is also set, diagnose P0611 first.

  1. Turn on the ignition, with the engine OFF.
  2. Observe the DTC information with a scan tool..

Does the scan tool display DTC P0611?

--

Go to DTC P0611

Go to Step 3

3
  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 4

Go to Intermittent Conditions

4

  1. Turn OFF the ignition.
  2. Disconnect the FICM. Refer to Fuel Injector Control Module Replacement .

    3. Important: Other DTC's may set.

  3. Turn ON the ignition, with the engine OFF.
  4. Probe the AFO enable circuit with a test lamp that is connected to B+.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 5

5

  1. Measure the resistance of the AFO enable circuit between the FICM connector terminal and ground with a DMM.
  2. Observe the circuit resistance as you command the AFO signal enable ON and OFF with a scan tool.

Does the circuit resistance change from a higher value on gasoline (OFF) to a lower value on alternative fuel (ON)

3000ohms

75ohms

Go to Step 8

Go to Step 6

6

Test the AFO enable circuit for an open or for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the G/H Van Service Manual.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

7

Test the AFO enable circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the G/H Van Service Manual.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

8

Inspect for poor connections at the harness connector of the FICM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the G/H Van Service Manual.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

9

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/H Van Service Manual.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

10

Replace the FICM. Refer to Fuel Injector Control Module Replacement .

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls in the G/H Van Service Manual.

Did you complete the replacement?

--

Go to Step 12

--

12
  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 13

13

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