P0641
DTC P0641 or P0651
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
DTC Descriptors
DTC P0641
- 5-Volt Reference 1 Circuit
DTC P0651
- 5-Volt Reference 2 Circuit
Diagnostic Fault Information
Circuit/System Description
The engine control module (ECM) has 2 internal 5-volt reference busses called 5-volt reference 1 and 5-volt reference 2. Each reference bus provides 5-volt reference circuits for more than one sensor. Therefore, a fault condition on one 5-volt reference circuit will affect the other 5-volt reference circuits connected to that reference bus. The ECM monitors the voltage on the 5-volt reference busses.
The 5-volt reference 1 bus provides 5 volts to the following sensors:
* The air conditioning (A/C) refrigerant pressure sensor
* The manifold absolute pressure (MAP) sensor
* The fuel tank pressure (FTP) sensor
* The accelerator pedal position (APP) sensor 2
* The camshaft position (CMP) sensors
* The Engine Oil Pressure (EOP) sensor
* The Supercharger Intake Air Pressure (SIAP) sensor
The 5-volt reference 2 bus provides 5 volts to the following sensors:
* The APP sensor 1
* The throttle position (TP) sensor 1 and 2
* The crankshaft position (CKP) sensor
Conditions for Running the DTC
* DTCs P0601, P0602, P0603, P0604, P0606, P0607, P060D, P062F, P1680 and P2610 are not set.
* The ignition is ON.
* The ignition voltage is more than 5.23 volts.
* 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-volt reference 1 or 2 bus for more than 0.5 second.
Action Taken When the DTC Sets
* The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
* The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.
Conditions for Clearing the MIL/DTC
* The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
* A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
* A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
* Clear the MIL and the DTC with a scan tool.
Reference Information
Schematic Reference
Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
P0641
1. Observe the MAP sensor voltage parameter with a scan tool with the ignition ON and the engine OFF. The scan tool should display approximately 2.2 volts for a normally operating system.
2. Engine running, observe the DTC information with a scan tool. DTCs P0641 or 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.
P0651
1. With the ignition ON and the engine OFF, observe the APP sensor 1 voltage parameter with a scan tool. The scan tool should display approximately 0.96 volt for a normally operating system.
2. Engine running, observe the DTC information with a scan tool. DTCs P0641 or 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
P0641
1. Disconnect the MAP sensor electrical connector.
2. With the ignition ON and the engine OFF, measure for 4.8-5.2 volts between the 5-volt reference circuit terminal C of the MAP sensor and ground.
• If the voltage is more than 5.2 volts, test for a short to voltage on the 5-volt reference circuits of all the sensors connected to the 5-volt reference 1 bus, test for a short to voltage on the FTP sensor signal circuit.
• If the voltage is less than 4.8 volts, test for a short to ground on the 5-volt reference circuits of all the sensors connected to the 5-volt reference 1 bus.
3. Continue to measure the voltage between the 5-volt reference circuit terminal C of the MAP sensor and ground. Monitor the DMM while disconnecting all other sensors connected to the 5-volt reference 1 bus, one at a time.
• If the voltage returns to 4.8-5.2 volts when a sensor is disconnected, replace the applicable sensor.
4. Reconnect all sensors.
5. Measure for 4.8-5.2 volts between the 5-volt reference circuit terminal B of the A/C refrigerant pressure sensor and ground.
• If the voltage is not between 4.8-5.2 volts, test for a short to voltage on the MAP sensor signal circuit or a faulty MAP sensor.
6. If all circuits test normal, replace the ECM.
P0651
1. Disconnect the throttle body electrical connector.
2. With the ignition ON and the engine OFF, measure for 4.8-5.2 volts between the 5-volt reference circuit terminal 3 and ground.
• If the voltage is more than 5.2 volts, test for a short to voltage on the 5-volt reference circuits on the 5-volt reference 2 bus.
• If the voltage is less than 4.8 volts, test for a short to ground on the 5-volt reference circuits on the 5-volt reference 2 bus.
3. Continue to measure the voltage between the 5-volt reference circuit terminal 3 of the throttle body electrical connector and ground. Monitor the DMM while disconnecting APP sensor 1.
• If the voltage returns to 4.8-5.2 volts when APP sensor 1 is disconnected, replace the APP sensor.
• If the voltage did not return to 4.8-5.2 volts when disconnecting the APP 1 sensor, replace the throttle body assembly.
4. If all circuits test normal, replace the ECM.
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)
* Fuel Tank Pressure Sensor Replacement (Service and Repair)
* Manifold Absolute Pressure Sensor Replacement (Service and Repair)
* Throttle Body Assembly Replacement (Removal and Replacement)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming