Powertrain Management (ECM, without L96)

DTC P0641 or P0651 (ECM, without L96)

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 provide 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 circuits. Each internal reference circuit provides external 5 V reference circuits for more than one sensor. A short to ground or short to voltage on one external 5 V reference circuit can affect all the components connected to the same internal 5 V reference circuit.

Conditions for Running the DTC

* The run/crank or powertrain relay voltage is greater than 6 V and reduced power is not active.

* 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 circuit 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 circuit provides 5 V to the following sensors:

* Manifold absolute pressure (MAP) sensor

* Fuel tank pressure (FTP) sensor

* Accelerator pedal position (APP) sensor 2

* Engine oil pressure (EOP) switch

* Air conditioning (A/C) refrigerant pressure sensor

* Camshaft position sensor

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

* APP sensor 1

* Throttle position sensor 1 and 2

* Crankshaft position sensor

* Brake pedal position sensor

It may be possible to locate the fault by disconnecting one component at a time from the appropriate 5 V reference circuit while viewing the 5-volt Reference 1 or 2 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 (except L96) [1][2]Electrical DiagramsEngine Controls Schematics (L96) [1][2]Electrical Diagrams

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)

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 Control Module References for scan tool information

Circuit/System Verification

1. Observe the scan tool 5-volt Reference 1 Circuit Status and the 5-volt Reference 2 Circuit Status parameters. Verify the parameters display OK.

2. Ignition ON, observe the DTC information with a scan tool. DTC P0641 and P0651 should not set.

3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Note:
Additional DTCs may set when disconnecting components.

1. Ignition ON, 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 of each affected component. 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 of each affected component. If all circuits test normal, replace the K20 ECM.

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

3. Connect each component associated with the 5 V reference circuit, one at a time, while monitoring the appropriate scan tool 5-volt Reference 1 or 2 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 (Non-HP2) Service and RepairAir Conditioning (A/C) Refrigerant Pressure Sensor Replacement (LGH, LML) Service and Repair

* Camshaft Position Sensor Replacement (With Actuator) Camshaft Position Sensor Replacement (With Actuator)Camshaft Position Sensor Replacement (Without Actuator) Camshaft Position Sensor Replacement (Without Actuator)

* Crankshaft Position Sensor Replacement Service and Repair

* Engine Oil Pressure Sensor and/or Switch Replacement Service and Repair

* Fuel Tank Pressure Sensor Replacement (25/35 Series) Service and RepairFuel Tank Pressure Sensor Replacement (15 Reg Cab With 26 Gal Tank) Service and RepairFuel Tank Pressure Sensor Replacement (15 Ext/Crew Cab With 26 Gal Tank) Service and RepairFuel Tank Pressure Sensor Replacement (15 Reg/Ext/Crew Cab w/34 Gal Tank) Service and Repair

* Manifold Absolute Pressure Sensor Replacement Service and Repair

* Throttle Body Assembly Replacement Removal and Replacement

* Control Module References Control Module References for ECM replacement, setup, and programming