P0651

DTC P0641 or P0651 (ECM w/o Supercharger)

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 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 buses called 5 V reference 1 and 5 V reference 2. Each reference bus provides 5 V reference circuits for more than one sensor. Therefore, a fault condition on one 5 V reference circuit will affect the other 5 V reference circuits connected to that reference bus. The ECM monitors the voltage on the 5 V reference buses.

Conditions for Running the DTC

* DTCs P0601, P0602, P0603, P0604, P0605, P0606, P060D, P062F and P2610 are not set.
* The ignition is ON.
* 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 tolerance condition on the 5 V reference 1 or 2 bus 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 bus 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
- B37B engine oil pressure (EOP) switch
- B1 air conditioning (A/C) refrigerant pressure sensor
- B23 camshaft position sensor

* The 5 V reference 2 bus provides 5 V to the following sensors:

- B107 APP sensor 1
- Q38 throttle position sensor 1 and 2
- B26 crankshaft position sensor
- B25B clutch pedal position sensor, if equipped

* It may be possible to locate the fault by disconnecting one component at a time from the affected 5 V reference bus while viewing the 5 V Reference Circuit Status parameter on the scan tool. The scan tool parameter will 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 (LS3) ([1][2]Electrical Diagrams) Engine Controls Schematics (LS7) ([1][2]Electrical Diagrams) Engine Controls Schematics (LS9) ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
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. Observe the scan tool 5 V reference 1 circuit status and the 5 V reference 2 circuit status parameters. Verify the parameters display OK.
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

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

1. Ignition OFF, disconnect the harness connector of all the sensors for the applicable DTC. Refer to Diagnostic Aids for the appropriate sensors.
2. Ignition ON, measure for 4.8-5.2 V between one of the 5 V reference circuits and ground.

• If less than the specified range, test for a short to ground on the 5 V reference circuit for each of the affected components. If all circuits test normal, replace the K20 ECM.
• If greater than the specified range, test for a short to voltage on the 5 V reference circuit for each of the affected components. 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 appropriate scan tool 5 V Reference Voltage parameter. Verify the voltage remains between 4.8-5.2 V.

• If not the specified range when a component is connected, test the signal circuit for a short to voltage. If the circuit tests normal, replace the appropriate component.

Repair Instructions

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

* Accelerator Pedal Position Sensor Replacement (Service and Repair)
* Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement (Service and Repair)
* Barometric Pressure Sensor Replacement (Service and Repair)
* Camshaft Position Sensor Replacement (Service and Repair)
* Clutch Pedal Position Sensor Replacement (Service and Repair)
* Crankshaft Position Sensor Replacement (Service and Repair)
* Fuel Tank Pressure Sensor Replacement (Service and Repair)
* Manifold Absolute Pressure Sensor Replacement (Without LS9) (Service and Repair)
* Throttle Body Assembly Replacement (Without LS9) (Removal and Replacement) Throttle Body Assembly Replacement (LS9) (Removal and Replacement)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming