P0641

DTC P0641 or P0651

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each of the diagnostic category.

DTC Descriptors
DTC P0641
- 5 V Reference 1 Circuit

DTC P0651
- 5 V Reference 2 Circuit

Circuit/System Description

The engine control module (ECM) has 2 internal 5 V reference busses called 5 V reference 1 and 5 V reference 2. Each reference buss provides 5 V reference circuits for more than one sensor. A fault condition on one 5 V reference circuit will affect the other 5 V reference circuits connected to that reference buss. The ECM monitors the voltage on the 5 V reference buss.

Conditions for Running the DTC

* DTCs P0601, P0602, P0603, P0604, P0605, P0606, P0607, and P2610 are not set.
* The ignition is in Unlock, Accessory, Run, or Crank.
* The ignition voltage is more than 5.23 V.
* DTCs P0641 and P0651 run continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects a voltage out of range condition on the 5 V reference 1 or 2 buss for more than 0.5 s.

Action Taken When the DTC Sets

DTCs P0641 and P0651 are Type A DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0641 and P0651 are Type A DTCs.

Diagnostic Aids

The 5 V reference 1 buss provides 5 V to the following sensors:

* B74 manifold absolute pressure (MAP) sensor
* B150 fuel tank pressure (FTP) sensor
* B107 accelerator pedal position (APP) sensor 2
* B1 air conditioning (A/C) refrigerant pressure sensor
* B23E exhaust camshaft position sensor
* B23F intake camshaft position sensor

The 5 V reference 2 buss provides 5 V to the following sensors:

* B107 APP sensor 1
* Q38 throttle position sensor 1 and 2
* B26 crankshaft position sensor
* Q30 air injector reactor (AIR) pressure sensor, if equipped

It may be possible to locate the fault by disconnecting one component at a time from the 5 V reference circuit while viewing the 5 V Reference circuit parameter on the scan tool. The scan tool parameter would change from Fault to OK when the source of the fault is disconnected.

If all 5 V reference components have been disconnected and a Fault is still indicated, the fault may exist in the wiring harness.

Reference Information
Schematic Reference

Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. With the ignition ON and the engine OFF, observe the 5 V Reference 1 and 2 parameters. The scan tool should display 4.8-5.2 V for a normally operating system.
2. Ignition ON, observe the DTC information with a scan tool. DTCs P0641 and P0651 should not set on this ignition cycle.
3. 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 data.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector of all appropriate sensors for the applicable DTC.

Note: A short to voltage on the signal circuit of certain components may cause this DTC to set.

2. Ignition ON, measure for 4.8-5.2 V between one of the 5 V reference circuits and ground.

• If the voltage is less than the specified value, test for a short to ground on all the 5 V reference circuits. If all circuits test normal, replace the K20 ECM.
• If the voltage is greater than the specified value, test for a short to voltage on all the 5 V reference circuits. If all circuits test normal, replace the K20 ECM.

3. Connect each component associated with the 5 V reference circuit, one at a time, while monitoring the voltage. Verify the voltage remains between 4.8-5.2 V.

• If the voltage display is not within the specified range when a component is connected, test the signal circuit for a short to voltage. If all circuits test normal, replace the component.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Accelerator Pedal with Position Sensor Assembly Replacement (Accelerator Pedal with Position Sensor Assembly Replacement)
* Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement (Service and Repair)
* Camshaft Position Sensor Replacement - Exhaust (Camshaft Position Sensor Replacement - Exhaust)
* Camshaft Position Sensor Replacement - Intake (Camshaft Position Sensor Replacement - Intake)
* Crankshaft Position Sensor Replacement (Service and Repair)
* Fuel Tank Pressure Sensor Replacement (Service and Repair)
* Manifold Absolute Pressure Sensor Replacement (Service and Repair)
* Secondary Air Injection Check Valve Replacement
* Throttle Body Assembly Replacement (Removal and Replacement)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming