Operation CHARM: Car repair manuals for everyone.

P0651



DTC P0641 or P0651

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0641
- 5-Volt Reference 1 Circuit

DTC P0651
- 5-Volt Reference 2 Circuit

Diagnostic Fault Information






Circuit/System Description

The engine control module (ECM) has 2 internal 5-volt reference circuits called 5-volt reference 1 and 5-volt reference 2. Each reference circuit 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 circuit. The ECM monitors the voltage on the 5-volt reference circuits.

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 circuit 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.

Diagnostic Aids

The 5-volt reference 1 circuit 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 circuit 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 brake booster vacuum sensor

It may be possible to locate the fault by disconnecting one component at a time from the affected 5-volt reference circuit while viewing the 5-Volt 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 disconnected. If all 5-volt reference components have been disconnected and a fault is still indicated, the fault may exist in the wiring harness.

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: A short to voltage on the signal circuit of certain components may cause this DTC to set.

1. Ignition OFF, disconnect the harness connector of all appropriate sensors for the applicable DTC.
2. Ignition ON, measure for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.

^ If less than the specified range, test for a short to ground on all the 5-volt reference circuits. 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. If all circuits test normal, replace the ECM.

3. Connect each component associated with the 5-volt reference circuit, one at a time, while monitoring the voltage. Verify the voltage remains between 4.8-5.2 volts.

^ If not within the specified range when a component is connected, test the signal circuit for a short to voltage. If the circuit tests normal, replace the appropriate component.

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
* Camshaft Position Sensor Replacement
* Crankshaft Position Sensor Replacement
* Engine Oil Pressure Sensor and/or Switch Replacement
* Fuel Tank Pressure Sensor Replacement
* Manifold Absolute Pressure Sensor Replacement
* Power Brake Booster Vacuum Sensor Replacement
* Throttle Body Assembly Replacement