P0651
DTC P0641 or P0651
Diagnostic Instructions
* Perform The Diagnostic System Check - Vehicle 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 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 secondary air injection (AIR) Solenoid
* The crankshaft position (CKP) sensor
* The camshaft position (CMP) 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 5-volt reference 1 circuit status parameter with a scan tool. The scan tool should display OK.
P0651
Observe the 5-volt reference 2 circuit status parameter with a scan tool. The scan tool should display OK.
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 or a short to voltage on the FTP sensor signal circuit. If the circuit tests normal, replace the 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 1 bus. If the circuit tests normal, replace the 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 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.
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 all the sensors connected to the 5-volt reference 2 bus. If the circuit tests normal, replace the 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 2 bus. If the circuit tests normal, replace the 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
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Accelerator Pedal Position Sensor Replacement
* Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
* Control Module References for ECM replacement, setup, and programming Programming and Relearning
* Fuel Tank Pressure Sensor Replacement
* Manifold Absolute Pressure Sensor Replacement
* Throttle Body Assembly Replacement