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: 5V Reference Circuit 1 MalfunctionDTC P0651: 5V Reference Circuit 2 Malfunction
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 | -- |
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 | -- |
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 buses 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 buses.
The 5 volt reference 1 bus provides 5 volts to the following sensors:
| • | The manifold absolute pressure (MAP) 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. |
Conditions for Running the DTC
| • | The ignition is in the Unlock/Accessory, Run or Crank position. |
| • | The ignition voltage is more than 12 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 or P0651 are type A DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0641 or P0651 are type A DTCs.
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
P0641
Ignition ON, engine OFF, observe the MAP sensor voltage parameter with a scan tool . The scan tool should display 3.6-4.8 volts for a normally operating system.
P0651
Ignition ON , engine OFF, observe the APP sensor 1 voltage parameter with a scan tool. The scan tool should display 0.75-1.25 volt for a normally operating system.
Circuit/System Testing
P0641
- Disconnect the MAP sensor harness connector.
- Ignition ON, engine OFF. Using DMM measure for 4.8-5.2 volts between the 5 volt reference circuit of the MAP sensor harness connector and a known ground.
- Continue to measure for 4.8-5.2 volts from the 5 volt reference circuit of the MAP sensor to a known ground.
| ⇒ | If the voltage is not within 4.8-5.2 volts, 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 that sensor. |
| ⇒ | If the voltage is within 4.8-5.2 volts, |
| ⇒ | Reconnect all sensors except the A/C refrigerant pressure sensor. If the A/C refrigerant pressure sensor is still connected, disconnect it. |
| ⇒ | Using a DMM measure for 4.8-5.2 volts between the 5 volt reference circuit of the A/C refrigerant pressure sensor harness connector and a known ground. |
| ⇒ | If the voltage is not within 4.8-5.2 volts, test for a short to voltage or an open/high resistance on the MAP sensor signal circuit or a faulty MAP sensor. |
Important: If a short to voltage occurs on the 5 volt reference circuit the A/C refrigerant pressure sensor may be damaged.
| ⇒ | 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 or a short to voltage on the FTP sensor signal circuit. If the circuits test normal, replace the ECM. |
| ⇒ | If the voltage is less than 4.8 volts, test for a short to ground or an open/high resistance on the 5 volt reference circuits of all the sensors connected to the 5 volt reference 1 bus. If the circuits test normal, replace the ECM. |
P0651
- Disconnect the throttle body harness connector.
- Ignition ON, engine OFF. Using a DMM measure for 4.8-5.2 volts between the 5 volt reference circuit of the throttle body harness connector and a known ground.
- Continue to measure for 4.8-5.2 volts between the 5 volt reference circuit of the throttle body harness connector and a known ground.
| ⇒ | If the voltage is not within 4.8-5.2 volts, monitor the DMM while disconnecting all other sensors connected to the 5 volt reference 2 bus, one at a time. If the voltage returns to 4.8-5.2 volts when a sensor is disconnected, replace the sensor. |
| ⇒ | If the voltage is within 4.8-5.2 volts, |
| ⇒ | Reconnect all sensors, leaving the accelerator pedal sensor module connector disconnected. If the accelerator pedal sensor module connector is still connected disconnect it. |
| ⇒ | Ignition ON, engine OFF. Using a DMM measure for 4.8-5.2 volts between the APP sensor 5 volt reference circuit of the APP sensor harness connector and a known ground. |
| ⇒ | If the voltage is not within 4.8-5.2 volts, replace the throttle body assembly. |
| ⇒ | 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 2 bus. If the circuits test normal, replace the ECM |
| ⇒ | If the voltage is less than 4.8 volts, test for a short to ground or an open/high resistance on the 5 volt reference circuits of all the sensors connected to the 5 volt reference 2 bus. If the circuits test normal, replace the ECM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup and programming |
