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: 5V Reference Circuit 1 Malfunction.
DTC P0651: 5V Reference Circuit 2 Malfunction.
DTC P0697: 5V Reference Circuit 3 Malfunction.

### 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 | --
Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit | P0641 | P0452 | P0641 | --
Manifold Absolute Pressure (MAP) Sensor 5-Volt Reference 1 Circuit | P0641 | P0107 | P0641 | --
Throttle Position (TP) Sensor 1 and 2 5-Volt Reference 2 Circuit | P0651 | P0122, P0222 | P0651 | --

### Circuit/System Description

The engine control module (ECM) has 3 internal 5-volt reference busses called 5-volt reference 1 and 5-volt reference 2 and 5-volt reference 3. 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 buses.

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

• | The manifold absolute pressure (MAP) 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 APP sensor 1.

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

• | The crankshaft position (CKP) sensor.

### Conditions for Running the DTC

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

• | The ignition voltage is more than 10.9 volts.

• | DTCs P0641, P0651 and P0697 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 3 bus for more than 0.5 second.

### Action Taken when the DTC Sets

DTCs P0641, P0651 and P0697 are type A DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0641, P0651 and P0697 are type A DTCs.

### 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

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

#### P0641

Ignition ON, engine OFF. Using a scan tool, observe the MAP sensor voltage parameter. The scan tool should display 3.6-4.8 volts for a normally operating system.

#### P0651

With the ignition ON and the engine OFF, observe the APP sensor 1 voltage parameter with a scan tool. The scan tool should display 0.3-0.6 volt for a normally operating system.

### Circuit/System Testing

1. Disconnect the MAP sensor harness connector.
2. With the ignition ON, engine OFF. Measure for 4.8-5.2 volts between the 5-volt reference circuit of the MAP sensor and a known ground.

⇒ | If the voltage is not within 4.8-5.2 volts, monitor the DMM while disconnecting all other sensors connected to the 5-volt reference 1 bus, one at a time. If the voltage returns to 4.8-5.2 volts when a sensor is disconnected, replace that sensor.

⇒ | If the voltage is within 4.8-5.2 volts,

⇒ | Reconnect all sensors except the A/C refrigerant pressure sensor. If the A/C refrigerant pressure sensor is still connected, disconnect it.

⇒ | Measure for 4.8-5.2 volts from the 5-volt reference circuit of the A/C refrigerant pressure sensor to ground with a DMM.

⇒ | If the voltage is not within 4.8-5.2 volts, test for a short to voltage on the MAP sensor signal circuit or a faulty MAP sensor.

3. Continue to measure for 4.8-5.2 volts from the 5-volt reference circuit of the MAP sensor to a known ground.

Important: If a short to voltage occurs on the 5-volt reference circuit, the A/C refrigerant pressure sensor may be damaged. If a short to voltage occurs on the fuel tank pressure (FTP) sensor signal circuit, the FTP sensor may be damaged.

⇒ | 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 or a short to voltage on the TP sensor signal circuit. If the circuits test normal, replace the ECM.

⇒ | 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. If the circuits test normal, replace the ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification.