P0651

DTC P0651

DTC DESCRIPTORS

DTC P0641
5-Volt Reference 1 Circuit

DTC P0651
5-Volt Reference 2 Circuit

DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection






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.

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
1. With the ignition OFF, disconnect the harness connector at the MAP sensor.
2. With the ignition ON, measure for 4.8-5.2 volts between the MAP sensor 5-volt reference circuit and ground.
3. Command the EGR valve to 100 percent while monitoring the MAP sensor 5-volt reference circuit with a DMM.
- If within 4.8-5.2 volts, refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics
4. With the ignition OFF, disconnect the harness connector at the EGR valve.
5. With the ignition ON, measure EGR valve 5-volt reference circuit.
- 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.
6. 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 the data parameters change with any component being disconnected, replace the component.
7. If all circuits tested are OK, replace the control module.

P0651
1. With the ignition OFF, disconnect the harness connector at the A/C pressure sensor.
2. With the ignition ON, measure for 4.8-5.2 volts between the A/C pressure sensor 5-volt reference circuit and ground.
- If within 4.8-5.2 volts, refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics
- If over 5.2 volts, test all 5-volt references circuits for a short to voltage. If all circuits tested are OK, 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.
3. If all circuits tested are OK, replace the control module.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Exhaust Gas Recirculation (EGR) Valve Replacement
- Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
- Control Module References for engine control module (ECM) replacement, setup, and programming
- Fuel Tank Pressure Sensor Replacement
- Manifold Absolute Pressure (MAP) Sensor Replacement (L32) Manifold Absolute Pressure (MAP) Sensor Replacement (L26)
- Barometric Pressure (BARO) Sensor Replacement Verification Tests