P0651
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 circuits. Each internal reference circuit provides 5 V reference 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
* Reduced engine power is not active.
* 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 range 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
* Air conditioning (A/C) refrigerant pressure sensor
* Exhaust camshaft position sensor
* Intake 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
* 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.
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 appropriate sensors for the applicable DTC.
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 the 5 V reference circuit for each affected component. 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 the 5 V reference circuit for 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 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 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 (NU5 or NT7) (Fuel Tank Pressure Sensor Replacement (NU5 or NT7))Fuel Tank Pressure Sensor Replacement (NU6) (Fuel Tank Pressure Sensor Replacement (NU6))
* Manifold Absolute Pressure Sensor Replacement (Service and Repair)
* Secondary Air Injection Check Valve Replacement (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