GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 GMC T-Series Medium Duty Truck F6/F7/F8 🢒 DTC 🢒 DTC P0651

Circuit Description

The engine control module (ECM) provides 5-volt reference voltage through the reference circuit 2 to the accelerator pedal position sensor. The ECM monitors the voltage on the 5-volt reference 2 circuit. If the ECM detects that the voltage is out of tolerance, this DTC will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0651 5-Volt Reference 2 Circuit

Conditions for Running the DTC
    • The ignition switch is ON.
    • The battery voltage is between 10-16 volts.

Conditions for Setting the DTC

When the 5-volt reference circuit 2 voltage is more than 5.5 volts or less than 4.5 volts.

Action Taken When the DTC Sets
    • The ECM illuminates the malfunction indicator lamp (MIL) and reduced engine power indicator lamp, if fitted, when the diagnostic runs and fails.
    • The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.

Conditions for Clearing the DTC
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

If an intermittent condition is suspected, the following may cause an intermittent:

    • Poor connections
    • Misrouted harness
    • Rubbed through wire insulation
    • Broken wire inside the insulation

Inspect for the following conditions:

    • Poor connection at ECM--Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    • Damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the DTC P0651 display on the scan tool while moving the connectors and wiring harness related to the sensor. A change in the display will indicate the location of the fault.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Observe the 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. You may also operate the vehicle within the conditions that you observed from the Failure Records.

Does the DTC fail this ignition?

--

Go to Step 3

Go to Diagnostic Aids

3
  1. Turn OFF the ignition.
  2. Disconnect the accelerator pedal position (APP) sensor connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the APP Sensor 2 parameter with a scan tool.

Is the APP Sensor 2 parameter within the specified range?

4.5-5.5 V

Go to Step 5

Go to Step 4

4
  1. Test the signal circuit between the engine control module (ECM) and the APP sensor 2 for the following conditions:
    2. • A short to ground circuit
    • A short to battery voltage
  2. Repair the circuits, as necessary.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 6

5

Replace the APP sensor. Refer to Accelerator Pedal Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 8

--

6
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Inspect for connections at the harness connector of the ECM.
  4. Repair the connections, as necessary.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

7

Important: The replacement ECM must be programmed.

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data , and Fuel Injector Flow Rate Programming .

Did you complete the replacement?

--

Go to Step 8

--

8
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  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 Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 9

9

Observe the stored information, Capture Info with a scan tool.

Are there any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK