Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC P0641: 5-Volt Reference 1 CircuitDTC P0651: 5-Volt Reference 2 Circuit
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Accelerator Pedal Position (APP) Sensor 1 5-Volt Reference 2 Circuit | P0651 | P2122 | P0651 | -- |
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference 1 Circuit | P0641 | P2127 | P0641 | -- |
Air Conditioning (A/C) Refrigerant Pressure Sensor 5-Volt Reference 1 Circuit | P0641 | P0532 | P0641 | -- |
Brake Booster Vacuum Sensor 5-Volt Reference 1 Circuit | P0641 | P0557 | P0641 | -- |
Camshaft Position (CMP) Sensor 5-Volt Reference 1 Circuit | P0641 | P0340 | P0641 | -- |
Engine Oil Pressure (EOP) Sensor 5-Volt Reference 1 Circuit | P0641 | P0522 | P0641 | -- |
Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit | P0641 | P0452 | P0641 | -- |
Manifold Absolute Pressure (MAP) Sensor 5-Volt Reference 1 Circuit | P0641 | P0107 | P0641 | -- |
The Crankshaft Position (CKP) Sensor 5-Volt Reference 2 Circuit | P0651 | P0335 | P0651 | -- |
Throttle Position (TP) Sensor 1 and 2 5-Volt Reference 2 Circuit | P0651 | P0122, P0222 | P0651 | -- |
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 manifold absolute pressure (MAP) sensor |
| • | The fuel tank pressure (FTP) sensor |
| • | The air conditioning (A/C) refrigerant pressure sensor |
| • | The accelerator pedal position (APP) sensor 2 |
| • | The engine oil pressure (EOP) sensor |
| • | The camshaft position (CMP) 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 |
| • | The cooling fan speed sensor |
Conditions for Running the DTC
| • | The ignition is in Unlock, Accessory, Run, or Crank. |
| • | 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
DTCs P0641 and P0651 are Type A DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0641 and P0651 are Type A DTCs.
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Circuit/System Verification
Ignition ON, observe the scan tool 5-volt reference 1 and 2 parameters. The reading should display Circuit OK for a normally operating system.
Circuit/System Testing
Important: Additional DTCs may set when disconnecting components.
- Ignition OFF, disconnect the harness connector of all the sensors connected to the 5-volt reference bus for the applicable DTC. Refer to Circuit/System Description.
- Ignition ON, test for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.
- Connect each component associated with the appropriate 5-volt reference bus, one at a time, while monitoring the voltage. The voltage should not change more than 1 volt.
Important: A short to voltage on the signal circuit of certain components may cause this DTC to set.
| ⇒ | If less than the specified range, test all of the 5-volt reference circuits for a short to ground. If all circuits test normal, replace the ECM. |
| ⇒ | If greater than the specified range, test for a short to voltage on all of the 5-volt reference circuits, or the signal circuit for each component associated with the appropriate 5-volt reference bus for a short to voltage. If all circuits test normal, replace the ECM. |
| ⇒ | If the voltage display changes more than the specified range when a component is connected, replace the component. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
