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 provide 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 |
|---|---|---|---|---|
Air Conditioning (A/C) Refrigerant Pressure Sensor 5-Volt Reference 2 Circuit | P0651 | P0532 | P0651 | -- |
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 | -- |
Exhaust Gas Recirculation (EGR) Valve 5-Volt Reference 1 Circuit | P0641 | P0404, P0405 | P0406 | -- |
Barometric Pressure (BARO) Sensor 5-Volt Reference 2 Circuit - L32 only | P0651 | P0069 | P0069 | -- |
AIR Pressure Sensor 5-Volt Reference 2 Circuit | P0651 | P2A32 | P0651 | -- |
Circuit/System Description
The control module 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 control module 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 exhaust gas recirculation (EGR) valve |
The 5-volt reference 2 bus provides 5 volts to the following sensors:
| • | Air conditioning (A/C) refrigerant pressure sensor |
| • | Barometric pressure (BARO) sensor |
Conditions for Running the DTC
| • | DTCs P0601, P0602, P0603, P0604, P0605, P0606, P0607, P060D, P062F, and P2610 are not set. |
| • | The ignition is ON. |
| • | The ignition voltage is more than 9.5 volts. |
| • | DTCs P0641 and P0651 run continuously when the above conditions are met. |
Conditions for Setting the DTC
The control module 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
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
P0641
Observe the MAP sensor voltage parameter with a scan tool with the ignition ON and the engine OFF. The scan tool should display 3.6-4.8 volts for a normally operating system.
P0651
With the ignition ON and the engine OFF, observe the A/C Refrigerant Pressure-A/C High Side Pressure parameter with a scan tool. The scan tool should display 0.2-4.9 volt or 9-453 psi for a normally operating system.
Circuit/System Testing
P0641
- With the ignition OFF, disconnect the harness connector at the MAP sensor.
- With the ignition ON, measure for 4.8-5.2 volts between the MAP sensor 5-volt reference circuit and ground.
- Command the EGR valve to 100 percent while monitoring the MAP sensor 5-volt reference circuit with a DMM.
- With the ignition OFF, disconnect the harness connector at the EGR valve.
- With the ignition ON, measure EGR valve 5-volt reference circuit.
- With the ignition ON, use a scan tool to observe the voltage parameter for each component associated with the 5-volt reference circuit while disconnecting each component one at a time.
- If all circuits tested are normal, replace the control module.
| ⇒ | If within 4.8-5.2 volts, refer to Testing for Intermittent Conditions and Poor Connections. |
| ⇒ | If within 4.8-5.2 volts, replace the EGR valve. |
| ⇒ | If over 5.2 volts, check for unexpected voltage at each 5-volt reference circuit or the signal circuit for each component associated with the 5-volt reference. |
| ⇒ | If under 4.8 volts, check for a short to ground or low reference circuit at each 5-volt reference circuit. |
| ⇒ | If the data parameters change with any component being disconnected, replace the component. |
P0651
- With the ignition OFF, disconnect the harness connector at the A/C pressure sensor.
- With the ignition ON, measure for 4.8-5.2 volts between the A/C pressure sensor 5-volt reference circuit and ground.
- If all circuits tested are normal, replace the control module.
| ⇒ | If within 4.8-5.2 volts, refer to Testing for Intermittent Conditions and Poor Connections. |
| ⇒ | If over 5.2 volts, test all 5-volt references circuits for a short to voltage. If all circuits tested are normal, replace the A/C pressure sensor. |
| ⇒ | If under 4.8 volts, turn OFF the ignition and test all 5-volt references circuits for a short to ground or any sensor low reference circuit. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for engine control module (ECM) replacement, setup, and programming |
