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P0651



DTC P0651

DIAGNOSTIC INSTRUCTIONS
- Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
- Strategy Based Diagnosis
- Diagnostic Procedure Instructions

DTC DESCRIPTORS

DTC P0641
5-Volt Reference 1 Circuit

DTC P0651
5-Volt Reference 2 Circuit

DIAGNOSTIC FAULT INFORMATION






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 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 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 approximately 2.2 volts for a normally operating system.

P0651
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.

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 from the 5-Volt reference circuit of the MAP sensor to ground with a DMM.
- 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. Measure the voltage from the 5-Volt reference circuit of the MAP sensor to 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 from the 5-Volt reference circuit of the A/C refrigerant pressure sensor to ground with a DMM.
- If the voltage is not within 4.8-5.2 volts, test for a short to voltage on the MAP sensor signal circuit or a faulty MAP sensor.
6. If no circuit faults were founded in the previous steps, inspect the ECM connector for damage. If the circuit tests normal, replace the control module.

P0651
1. Disconnect the throttle body electrical connector.
2. With the ignition ON and the engine OFF, measure for 4.8-5.2 volts from the 5-Volt reference circuit to ground with a DMM.
- If the voltage is more than 5.2 volts, test for a short to voltage on the 5-Volt reference circuits of 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 of the 5-Volt reference 2 bus.
3. Continue to measure the voltage from the 5-Volt reference circuit of the throttle body electrical connector to 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 no circuit faults were founded in the previous steps, inspect the ECM connector for damage. If the circuit tests normal, replace the control module.

REPAIR INSTRUCTIONS
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Accelerator Pedal Position Sensor Replacement
- Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
- Control Module References for ECM replacement, setup, and programming
- Fuel Tank Pressure Sensor Replacement
- Manifold Absolute Pressure Sensor Replacement
- Throttle Body Assembly Replacement Verification Tests
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