GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Conventional) C6/C7/C8 🢒 DTC 🢒 DTC P0641

Circuit Description

The engine control module (ECM) provides a 5-volt reference to the following sensors:

    • The accelerator pedal position sensor
    • The power take off (PTO) accelerator position sensor
    • The oil pressure sensor
    • Boost sensor
    • The exhaust gas recirculation (EGR) position sensor
    • The variable nozzle turbo (VNT) position sensor
    • The fuel rail pressure sensor

The 5-volt reference circuits are independent of each other outside the ECM, but are bussed together inside the ECM. Therefore, a circuit condition on one sensor 5-volt reference circuit may affect the sensor 5-volt reference 1 circuits. The ECM monitors the voltage on the 5-volt reference 1 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 P0641 5-Volt Reference 1 Circuit

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

Conditions for Setting the DTC

The 5-volt reference circuit 1 voltage is more than 5.5 volts or less than 4.5 volts.

Action Taken When the DTC Sets
    • The ECM limits fuel injection quantity for fail-safe operation.
    • The ECM limits fuel pressure for fail-safe operation.
    • The ECM closes the EGR valve and holds it in the closed position.
    • The PTO control is inhibited.
    • 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.
    • The ECM inhibits the cruise control.

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

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 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 Intermittent Conditions

3
  1. Turn OFF the ignition.
  2. Disconnect the accelerator pedal position (APP) sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the 5-volt reference circuit of the APP 1 sensor to a known good ground with a DMM.

Is the voltage within the specified range?

4.5-5.5 V

Go to Step 7

Go to Step 4

4
  1. Observe the DMM while disconnecting all other components connected to the 5-volt reference 1 circuit, one at a time.
  2. If voltage changes when one of the components are disconnected, replace the component. Refer to the appropriate replacement procedure.

Was a component replaced?

--

Go to Step 8

Go to Step 5

5
  1. Test each 5-volt reference 1 circuit for the following conditions:
    2. • A short to ground circuit
    • A short to battery voltage or ignition voltage
  2. Repair the circuits as necessary.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 6

6

Important: The replacement engine control module (ECM) must be programmed.

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

Did you complete the replacement?

--

Go to Step 8

--

7

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

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