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

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage
--- | --- | --- | ---
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference 1 Circuit | P0641, P2228, P0532, P0452, P0107 | P2127 | P0533, P0641, P2229, P2261
Accelerator Pedal Position (APP) Sensor 1 5-Volt Reference 2 Circuit | P0651 | P2122 | P0651
Air Conditioning (A/C) Refrigerant Pressure Sensor 5-Volt Reference 1 Circuit | P0641, P0107, P0 452, P0532, P2228, P0069, P0522, P0 390, P0365, P0345, P0340¹ |  |
Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit | P0641 P0107, P0452, P0532, P2228, P0069, P0522, P0390, P0365, P0345, P0340 |  |
Manifold Absolute Pressure (MAP) Sensor 5-Volt Reference 2 Circuit | P0651, P2228, P0532, P0452, P0107, P0522 |  |
Throttle Position (TP) Sensor 1 and 2 5-Volt Reference 1 Circuit | P0641 |  |
Engine Oil Pressure (EOP) Sensor 5-Volt Reference 1 Circuit | P0641, P0107, P0 452, P0532, P2228, P0069, P0522, P0 390, P0365, P0345, P0340¹ |  |
Crankshaft Position (CKP) Sensor 5-Volt Reference 2 Circuit | P0651 |  |
Camshaft Position (CMP) Sensor Bank 1 Exhaust 5-Volt Reference 1 Circuit | P0641 P0107, P0452, P0532, P2228, P0069, P0522, P0390, P0365, P0345, P0340 |  |
Camshaft Position (CMP) Sensor Bank 1 Intake 5-Volt Reference 1 Circuit | P0641 P0107, P0452, P0532, P2228, P0069, P0522, P0390, P0365, P0345, P0340 |  |
Camshaft Position (CMP) Sensor Bank 2 Exhaust 5-Volt Reference 1 Circuit | P0641 P0107, P0452, P0532, P2228, P0069, P0522, P0390, P0365, P0345, P0340 |  |
Camshaft Position (CMP) Sensor Bank 2 Intake 5-Volt Reference 1 Circuit | P0641 P0107, P0452, P0532, P2228, P0069, P0522, P0390, P0365, P0345, P0340 |  |
¹Engine cranks but does not start

### Circuit/System Description

The control module has 2 internal 5-volt reference busses called 5-volt reference 1 and 5-volt reference 2. Each reference bus provides a 5-volt reference for more than one sensor. Therefore, a fault condition at one 5-volt reference circuit will affect the other 5-volt reference circuits connected to that reference bus. The control module monitors the voltage on the 5-volt reference bus.

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

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

• | The throttle position (TP) sensor 1 and 2

• | The fuel tank pressure (FTP) sensor

• | The accelerator pedal position (APP) sensor 2

• | Camshaft Position (CMP) Sensor

• | The Engine Oil Pressure (EOP) sensor

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

• | The APP sensor 1

• | Crankshaft Position (CKP) Sensor

• | The Manifold Absolute Pressure (MAP) Sensor

### Conditions for Running the DTC

• | DTC P0601, P0602, P0603, P0604, P0606, P0607, P060D, P062F, P1680, P2610 are not set.

• | The ignition switch is in Unlock, Accessory, Run or Crank.

• | The ignition voltage is greater than 5.23 volts.

• | DTCs P0641 and P0651 run continuously when the above conditions are met.

### Conditions for Setting the DTC

• | The control module detects a voltage out of tolerance condition on the 5-volt reference 1 or 2 bus.

• | It occurs 39 times during the 19 tests.

### Action Taken When the DTC Sets

DTCs P0641 and P0651 are Type A DTCs.

### Conditions for Clearing the DTC

DTCs P0641 and P0651 are Type A DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Scan Tool Data List

### Circuit/System Verification

#### P0641

With the engine OFF, turn the igniton ON, observe the MAP sensor voltage parameter with a scan tool. When the system is operating correctly, the scan tool should display approximately 2.2 volts.

#### P0651

With the engine OFF, turn the ignition ON, observe the APP sensor 1 voltage parameter with a scan tool. When the system is operating correctly, the scan tool should display approximately 0.96 volt.

### Circuit/System Testing

#### P0641

1. Disconnect the throttle body electrical connector.
2. With the engine OFF, turn the ignition ON, measure the MAP sensor for 4.8-5.2 volts between the 5-volt reference circuit terminal E and ground.

⇒ | If the voltage is more than 5.2 volts, test for a short to voltage on the 5-volt reference circuits of all the sensors connected to the 5-volt reference 1 bus, test for a short to voltage on the FTP sensor signal circuit.

⇒ | If the voltage is less than 4.8 volts, test for a short to ground on the 5-volt reference circuits of all the sensors connected to the 5-volt reference 1 bus.

3. Continue to measure the voltage between the throttle 5-volt reference circuit terminal E and ground. Monitor the DMM while disconnecting all other sensors connected to the 5-volt reference 1 bus.

⇒ | If the voltage returns to 4.8-5.2 volts when a sensor is disconnected, replace the applicable sensor.

4. Reconnect all sensors.
5. Measure for 4.8-5.2 volts from the 5 volt reference circuit terminal B of the A/C refrigerant pressure sensor to ground.

⇒ | If the voltage is not within 4.8-5.2 volts, test the throttle body signal circuit for a short to voltage or the throttle body is inoperative.

6. If all circuits test normal, replace the ECM.

#### P0651

1. Disconnect the MAP sensor electrical connector.
2. With the engine OFF, turn the igniton ON, measure for 4.8-5.2 volts between the 5-volt reference circuit terminal C and ground.

⇒ | If the voltage is more than 5.2 volts, test for a short to voltage on the 5-volt reference circuits of the 5-volt reference 2 bus.

⇒ | If the voltage is less than 4.8 volts, test for a short to ground on the 5-volt reference circuits of the 5-volt reference 2 bus.

3. Continue to measure the MAP sensor electrical connector between the 5-volt reference circuit terminal C and ground. Monitor the DMM while disconnecting APP sensor 1.

⇒ | If the voltage returns to 4.8-5.2 volts when APP sensor 1 is disconnected, replace the APP sensor.

⇒ | If the voltage returns to 4.8-5.2 volts when APP sensor 1 is disconnected, replace the MAP sensor.

4. If all circuits test normal, replace the ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Accelerator Pedal Position Sensor Replacement Accelerator Pedal Position 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