GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC K Sierra - 4WD (CNG) 🢒 Engine 🢒 Engine Controls - 6.0L 🢒 DTC P1650

Circuit Description

The AF fuel pump relay disables the gasoline fuel pump when the engine is operating on CNG. The alternative fuels ECM turns the relay ON about 2 seconds after the engine is cranked or started on gasoline. The alternative fuels ECM monitors the voltage on the AF fuel pump relay control circuit. If the alternative fuels ECM detects an incorrect voltage on the AF fuel pump relay control circuit, DTC P1650 sets.

Conditions for Running the DTC

The ignition voltage is between 6-18 volts.

Conditions for Setting the DTC
    • The alternative fuels ECM detects that the commanded state of the driver and the actual state of the control circuit do not match.
    • All the above conditions are present for a minimum of 2 seconds.

Action Taken When the DTC Sets
    • The alternative fuels ECM will not illuminate the MIL.
    • The alternative fuels ECM will store this DTC as History during one drive trip in which the diagnostic runs and fails.
    • The alternative fuels ECM will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data.

Conditions for Clearing the DTC
    • The Last Test Failed status will clear when the DTC runs and passes.
    • The History status will clear after 40 consecutive warm-up cycles with no failures of any DTC.
    • All DTC information can be cleared using a scan tool.

Test Description

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

  1. Listen for a click when the relay operates. Command both the ON and the OFF states. Repeat the commands as necessary.

    2.

  2. This step verifies that the alternative fuels ECM is providing a ground to the AF fuel pump relay.

    3.

  3. This step tests for an open in the power circuit to the AF fuel pump relay.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Alternative Fuels Diagnostic System Check-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. With a scan tool, command the AF fuel pump relay ON and OFF.

Does the AF fuel pump relay turn ON and OFF with each command?

Go to Step 3

Go to Step 4

3
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text, or as close as possible to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 4

Go to Intermittent Conditions

4

  1. Turn OFF the ignition.
  2. Disconnect the AF fuel pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the control circuit of the AF fuel pump relay with a test lamp connected to battery positive.
  5. With a scan tool, command the AF fuel pump relay ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 5

Go to Step 6

5

  1. Connect a test lamp between the control circuit of the AF fuel pump relay and the coil power circuit of the relay.
  2. With a scan tool, command the AF fuel pump relay ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 9

Go to Step 11

6

Does the test lamp remain illuminated with each command?

Go to Step 8

Go to Step 7

7

Test the control circuit of the fuel pump relay for a short to power or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 14

Go to Step 10

8

Test the control circuit of the fuel pump relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 14

Go to Step 10

9

Inspect for poor connections at the AF fuel pump relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup 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 connectors of the alternative fuels ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 14

Go to Step 13

11

Repair the coil power circuit of the relay. Refer to Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you complete the repair?

Go to Step 14

--

12

Replace the AF fuel pump relay.

Did you complete the replacement?

Go to Step 14

--

13

Replace the alternative fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement .

Did you complete the replacement?

Go to Step 14

--

14
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 15

Go to Step 2

15

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK