P0641
DTC P0641 or P0651
DTC Descriptors
DTC P0641
- 5-Volt Reference 1 Circuit
DTC P0651
- 5-Volt Reference 2 Circuit
Diagnostic Fault Information
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
Circuit/System Description
The engine control module (ECM) 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 ECM 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 air conditioning (A/C) refrigerant pressure sensor
* The accelerator pedal position (APP) sensor 2
* The engine oil pressure (EOP) sensor
* The camshaft position (CMP) 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
* The cooling fan speed sensor (GMT 360/370 only)
Conditions for Running the DTC
* The ignition is in Unlock, Accessory, Run, or Crank.
* 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 ECM 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
DTCs P0641 and P0651 are Type A DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0641 and P0651 are Type A DTCs.
Circuit/System Verification
Ignition ON, observe the scan tool 5-volt reference 1 and 2 parameters. The reading should display Circuit OK for a normally operating system.
Circuit/System Testing
Important: Additional DTCs may set when disconnecting components.
1. Ignition OFF, disconnect the harness connector of all the sensors connected to the 5-volt reference bus for the applicable DTC. Refer to Circuit/System Description.
Important: A short to voltage on the signal circuit of certain components may cause this DTC to set.
2. Ignition ON, test for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.
• If less than the specified range, test all of the 5-volt reference circuits for a short to ground. If all circuits test normal, replace the ECM.
• If greater than the specified range, test for a short to voltage on all of the 5-volt reference circuits, or the signal circuit for each component associated with the appropriate 5-volt reference bus for a short to voltage. If all circuits test normal, replace the ECM.
3. Connect each component associated with the appropriate 5-volt reference bus, one at a time, while monitoring the voltage. The voltage should not change more than 1 volt.
• If the voltage display changes more than the specified range when a component is connected, replace the component.
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
* Fuel Tank Pressure Sensor Replacement
* Manifold Absolute Pressure Sensor Replacement
* Throttle Body Assembly Replacement
* Engine Oil Pressure Sensor and/or Switch Replacement
* Camshaft Position Sensor Replacement
* Crankshaft Position Sensor Replacement Verification Tests