Powertrain Management
DTC P0641 or P0651
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provide an overview of each diagnostic category.
DTC Descriptors
DTC P0641
- 5 V Reference 1 Circuit
DTC P0651
- 5 V Reference 2 Circuit
Circuit/System Description
The engine control module (ECM) has 2 internal 5 V reference busses called 5 V reference 1 and 5 V reference 2. Each reference bus provides 5 V reference circuits for more than one sensor. Therefore, a fault condition on one 5 V reference circuit will affect the other 5 V reference circuits connected to that reference bus. The ECM monitors the voltage on the 5 V reference busses.
Conditions for Running the DTC
* The ignition is in Unlock, Accessory, Run, or Crank.
* The ignition voltage is more than 5.23 V.
* 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 V reference 1 or 2 bus for more than 0.5 s.
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.
Diagnostic Aids
P0641
The 5 V reference 1 bus provides 5 V to the following sensors:
* B74 manifold absolute pressure (MAP) sensor
* B150 fuel tank pressure (FTP) sensor
* B1 air conditioning (A/C) refrigerant pressure sensor
* B107 accelerator pedal position (APP) sensor 2
* B37B engine oil pressure (EOP) sensor
* B23 camshaft position sensor
The 5 V reference 2 bus provides 5 V to the following sensors:
* B107 APP sensor 1
* Q38 throttle position sensor 1 and 2
* B26 crankshaft position sensor
It may be possible to locate the fault by disconnecting one component at a time fro the affected 5 V reference circuit while viewing the 5 V Reference Circuit Status parameter on the scan tool. The scan tool parameter will change from Fault to OK when the source of the fault is disconcerted. If all 5 V reference components have been disconnected and a fault is still indicated, the fault may exist in the wiring harness.
Reference Information
Schematic Reference
Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Control Module References (Programming and Relearning)for scan tool information
Circuit/System Verification
Ignition ON, observe the scan tool 5 V reference 1 and 2 parameters. The reading should display Circuit OK for a normally operating system.
Circuit/System Testing
Note: Additional DTCs may set when disconnecting components.
1. Ignition OFF, disconnect the harness connector of all the sensors connected to the 5 V reference bus for the applicable DTC. Refer to Circuit/System Description.
Note: 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 V between one of the 5 V reference circuits and ground.
• If less than the specified range, test all of the 5 V reference circuits for a short to ground. If all circuits test normal, replace the K20 ECM.
• If greater than the specified range, test for a short to voltage on all of the 5 V reference circuits, or the signal circuit for each component associated with the appropriate 5 V reference bus for a short to voltage. If all circuits test normal, replace the K20 ECM.
3. Connect each component associated with the appropriate 5 V reference bus, one at a time, while monitoring the voltage. The voltage should not change more than 1 V.
• 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 (Verification Tests) after completing the diagnostic procedure.
* Accelerator Pedal Position Sensor Replacement (Service and Repair)
* Camshaft Position Sensor Replacement (Service and Repair)
* Crankshaft Position Sensor Replacement (Crankshaft Position Sensor Replacement)
* Engine Oil Pressure Sensor and/or Switch Replacement (Service and Repair)
* Fuel Tank Pressure Sensor Replacement (Regular Cab with 26 Gallon Tank) (Service and Repair)Fuel Tank Pressure Sensor Replacement (Regular Cab with 34 Gallon Tank) (Service and Repair)Fuel Tank Pressure Sensor Replacement (Extended Cab with 26 Gallon Tank) (Service and Repair)
* Manifold Absolute Pressure Sensor Replacement (Service and Repair)
* Throttle Body Assembly Replacement (Removal and Replacement)
* Control Module References (Programming and Relearning)for ECM replacement, setup, and programming