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 of the diagnostic category.

### DTC Descriptors

DTC P0641: 5-Volt Reference 1 Circuit
DTC P0651: 5-Volt Reference 2 Circuit

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Accelerator Pedal Position (APP) Sensor 1 5-Volt Reference 2 Circuit | P0651 | P2122 | P0651 | --
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference 1 Circuit | P0641 | P2127 | P0641 | --
Air Conditioning (A/C) Refrigerant Pressure Sensor 5-Volt Reference 1 Circuit | P0641 | P0532 | P0641 | --
Crankshaft Position Sensor 5-Volt Reference 2 Circuit | P0651 | P0335 | P0651 | --
Exhaust Camshaft Position Sensor 5-Volt Reference 1 Circuit | P0641 | P0365 | P0641 | --
Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit | P0641 | P0452 | P0641 | --
Intake Camshaft Position Sensor 5-Volt Reference 1 Circuit | P0641 | P0340 | P0641 | --
Manifold Absolute Pressure (MAP) Sensor 5-Volt Reference 1 Circuit | P0641 | P0107 | P0641 | --
Throttle Position (TP) Sensor 1 5-Volt Reference 2 Circuit | P0651 | P0122 | P0651 | --
Throttle Position (TP) Sensor 2 5-Volt Reference 2 Circuit | P0651 | P0222 | P0651 | --

### 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 exhaust camshaft position (CMP) sensor

• | The intake 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

### Conditions for Running the DTC

• | DTCs P0601, P0602, P0603, P0604, P0605, P0606, P0607, and P2610 are not set.

• | 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

DTC P0641 and P0651 are type A DTCs.

### Conditions for Clearing the MIL/DTC

DTC P0641 and P0651 are type A DTCs.

### Diagnostic Aids

It may be possible to locate the fault by disconnecting one component at a time from the 5-volt reference circuit while viewing the 5-Volt Reference circuit parameter on the scan tool. The scan tool parameter would 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.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Controls Connector End Views

• | Engine Control Module 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

### Circuit/System Verification

With the ignition ON and the engine OFF, observe the 5-volt Reference 1 and 2 parameters . The scan tool should display 4.8-5.2 volts for a normally operating system.

### Circuit/System Testing

Important: Additional DTCs will set when disconnecting the components.

1. Ignition OFF, disconnect the harness connector of all appropriate sensors for the applicable DTC.

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

2. Ignition ON, measure for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.

⇒ | If the voltage is less than the specified value, test for a short to ground on all the 5-volt reference circuits. If all circuits test normal, replace the control module.

⇒ | If the voltage is greater than the specified value, test for a short to voltage on all the 5-volt reference circuits. If all circuits test normal, replace the control module.

3. Connect each component associated with the 5-volt reference circuit, one at a time, while monitoring the voltage. The voltage should not change more than 1 volt.

⇒ | If the voltage display increases greater than the specified value when a component is connected, test the signal circuit for a short to voltage. If all circuits test normal, replace the control module.

⇒ | If the voltage display decreases more than the specified value when a component is connected, replace the component.

### Repair Instructions

• | Accelerator Pedal Position Sensor Replacement

• | Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement

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

• | Fuel Tank Pressure Sensor Replacement

• | Manifold Absolute Pressure Sensor Replacement

• | Throttle Body Assembly Replacement

• | Camshaft Position Sensor Replacement - Intake

• | Camshaft Position Sensor Replacement - Exhaust

• | Crankshaft Position Sensor Replacement

### Repair Verification

With the ignition ON and the engine OFF, observe the 5-Volt Reference 1 and 2 parameters. The scan tool should display 4.8-5.2 volts for a normally operating system.