Powertrain Management (ECM)
DTC P0641 or P0651 (ECM Without 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 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 the other components connected to the same internal 5 V reference circuit.
Conditions for Running the DTC
* Reduced engine power is not active.
* The ignition is ON.
* The ignition voltage is more than 6 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 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) sensor
- 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
- Clutch pedal position sensor, if equipped
- Brake pedal position sensor, LS3 with automatic transmission
* It may be possible to locate the fault by disconnecting one component at a time from the affected 5 V reference circuit 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 DiagramsEngine Controls Schematics (LS9) [1][2]Electrical DiagramsEngine Controls Schematics (LS7) [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Folding Top 5 Bow Lowered Switch (CM7)
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 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.
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:
Additional DTCs will set when disconnecting the components.
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.
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 V Reference Voltage parameter. Verify the voltage remains between 4.8-5.2 V.
• If not within 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
* Camshaft Position Sensor Replacement Service and Repair
* Clutch Pedal Position Sensor Replacement Service and Repair
* Crankshaft Position Sensor Replacement Service and Repair
* Engine Oil Pressure Sensor and/or Switch Replacement
* 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 ReplacementThrottle Body Assembly Replacement (LS9) Removal and Replacement
* Control Module References Control Module References for ECM replacement, setup, and programming