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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 accelerator pedal position (APP) sensor 2
- The clutch pedal position (CPP) switch
- The engine oil pressure (EOP) switch
- The camshaft position (CMP) sensor

The 5-Volt reference 2 bus provides 5 volts to the following sensors:
- The acceleration pedal position (APP) sensor 1
- The throttle position (TP) sensor 1 and 2
- The air conditioning (A/C) refrigerant pressure sensor
- The crankshaft position (CKP) 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

DTC 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.

DTC 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 0.3-0.6 volt for a normally operating system.

CIRCUIT/SYSTEM TESTING

DTC 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 A bus, a short to voltage on the FTP sensor signal circuit, or a faulty control module.
- 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 A bus, or a faulty control module.
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 A 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 except the EOP sensor.
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.

DTC 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 APP sensor 1 and TP sensor 1 and 2 or for a faulty control module.
- If the voltage is less than 4.8 volts, test for a short to ground on the 5-Volt reference circuits of APP sensor 1 and TP sensor 1 and 2, or a faulty control module.
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.
4. Connect the throttle body electrical connector.
5. 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 not within 4.8-5.2 volts, replace the throttle body assembly.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Accelerator Pedal Position (APP) 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 (MAP) Sensor Replacement
- Throttle Body Assembly Replacement Verification Tests
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