For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | 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

### Circuit/System Description

The engine control module (ECM) has 2 5-volt reference circuits. The ECM provides the 5-volt reference to various sensors. Each reference circuit provides a 5-volt reference for greater than one sensor. A short to ground or voltage on one of the 5-volt reference circuits will affect all components connected to that 5-volt reference circuit. The ECM monitors the voltage on the 5-volt reference circuits.

### Conditions for Running the DTC

• | The ignition is ON.

• | DTCs P0641 and P0651 run continuously when the above condition is met.

### Conditions for Setting the DTC

The control module detects a voltage above 5.5 volts, or below 4.5 volts, on either 5-volt reference circuit for greater than 0.5 second.

### Action Taken When the DTC Sets

• | DTCs P0641 and P0651 are Type B DTCs.

• | The ECM commands the TAC system to operate in a Reduced Engine Power mode.

### Conditions for Clearing the DTC

DTCs P0641 and P0651 are Type B DTCs.

### Diagnostic Aids

• | If a shared 5-volt reference circuit is shorted to ground or shorted to a voltage, other 5-volt reference circuits may be affected.

• | The scan tool 5 volt reference parameter should display between 4.6-5.4 volts.

#### P0641

The 5-volt reference 1 circuit provides 5 volts to the following sensors:

• | The accelerator pedal position (APP) sensor 1

• | The throttle position (TP) sensor 1

• | The throttle position (TP) sensor 2

#### P0651

The 5-volt reference 2 circuit provides 5 volts to the following sensors:

• | The accelerator pedal position (APP) sensor 2

• | The air conditioning (A/C) refrigerant pressure sensor

• | The exhaust gas recirculation (EGR) valve

• | The fuel tank pressure (FTP) sensor

• | The intake manifold tuning (IMT) valve position sensor

• | The manifold absolute pressure (MAP) sensor

• | The rough road sensor

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. DTCs P0641 and P0651 should not set.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

Important: Additional DTCs will set when disconnecting the components.

1. Ignition OFF, disconnect the harness connector at all appropriate sensors for the applicable DTC. Refer to Diagnostic Aids.
2. Ignition ON, test for 4.6-5.4 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 control module.

⇒ | If greater than the specified range, test for a short to voltage on all the 5-volt reference circuits for each component associated with the appropriate 5-volt reference circuit. If all circuits test normal, replace the control module.

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

3. Connect each component associated with the 5-volt reference circuit one at a time while monitoring the scan tool 5 volt reference parameter. The voltage should not change greater than 0.5 volt.

⇒ | If not within 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

• | Exhaust Gas Recirculation Valve Replacement

• | Fuel Tank Pressure Sensor Replacement

• | Intake Manifold Tuning Valve Actuator Solenoid Replacement

• | Manifold Absolute Pressure Sensor Replacement

• | Rough Road Sensor Replacement

• | Throttle Body Assembly Replacement

• | Control Module References for ECM replacement, setup, and programming