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 Descriptor

DTC P0641 00: 5V Reference 1 Circuit Malfunction

### Circuit/System Description

The engine control module (ECM) has three 5-volt reference circuits. The ECM provides the 5-volt reference to various sensors. Each reference circuit provides a 5-volt reference for more 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.

• | The DTCs run continuously when the above condition is met.

### Conditions for Setting the DTC

The control module detects a voltage above 5.5 V or below 4.5 V on any of the 5-volt reference circuits for greater than 0.5 s.

### Action Taken When the DTC Sets

• | DTC P0641 is a Type B DTC.

• | The ECM commands the throttle actuator control (TAC) system to operate in a Reduced Engine Power mode.

### Conditions for Clearing the DTC

DTC P0641 is a Type B DTC.

### 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.

#### P0641

The 5-volt reference 1 circuit provides 5 V to the accelerator pedal position (APP) sensor 2, A/C refrigerant pressure sensor, throttle position sensor, exhaust gas recirculation (EGR) valve, turbocharger vane position sensor, clutch pedal position (CPP) sensor and diesel particulate filter pressure sensor

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### 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. DTC P0641 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

Note: 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 V between the 5-volt reference circuit and ground.

⇒ | If the voltage is less than the specified range, test the 5-volt reference circuit for a short to ground. If all circuits test normal, replace the K20 Engine Control Module (ECM).

⇒ | If greater than the specified range, test the 5-volt reference circuit for each component associated with the 5-volt reference circuit for a short to voltage. If all circuits test normal, replace the K20 Engine Control Module (ECM).

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

3. Observe the scan tool that DTC P0641 is not set while connecting each component associated with the 5-volt reference circuit one at a time..

⇒ | If the DTC set when a component is connected, test the signal circuit for a short to voltage. If all circuits test normal, 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

• | Throttle Body Assembly Replacement

• | Exhaust Gas Recirculation Valve Replacement

• | LINK

• | Clutch Pedal Position Switch Replacement

• | LINK

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