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 P0642 00: 5-Volt Reference 1 Circuit Low Voltage
DTC P0643 00: 5-Volt Reference 1 Circuit High Voltage
DTC P0652 00: 5-Volt Reference 2 Circuit Low Voltage
DTC P0652 00: 5-Volt Reference 2 Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Air Conditioning (A/C) Refrigerant Pressure Sensor 5-Volt Reference 1 Circuit | P0642 00 | P0532 00 | P0643 00, P0533 00 | --
Manifold Absolute Pressure Sensor 5-Volt Reference 1 Circuit | P0642 00, P0107 00 | P0642 00 | P0643 00, P0108 00 | --
Clutch Pedal Position (CPP) Sensor 5-Volt Reference 1 Circuit | P0642 00, P0807 00 | P0642 00, P0807 00 | P0643 00 | --
Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit | P0642 00 | -- | P0643 00 | --
Crankshaft Position Sensor 5-Volt Reference 2 Circuit | P0652 00 | P0335 00 | P0653 00 | --

### Circuit/System Description

The engine control module (ECM) has 2 internal 5-volt reference circuits called 5-volt reference 1 and 5-volt reference 2. Each reference circuit provides 5-volt reference circuits for more than one sensor. A fault condition on one 5-volt reference circuit will affect the other 5-volt reference circuits connected to that reference circuit. The ECM monitors the voltage on the 5-volt reference circuits.

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

• | The A/C refrigerant pressure sensor

• | The manifold absolute pressure (MAP) sensor

• | The clutch pedal position (CPP) sensor

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

The crankshaft position sensor

### Conditions for Running the DTC

• | DTCs P0601 00, P0602 00, P0604 00, P0606 00, P0607 00, and P2610 00 are not set.

• | The ignition is in unlock, accessory, run, or crank.

• | The ignition voltage is more than 5.23 V.

• | DTCs P0642 00, P0643 00, P0652 00 and P0653 00 run continuously when the above conditions are met.

### Conditions for Setting the DTC

The ECM detects a voltage out of range condition on the 5-volt reference 1 or 2 buss for more than 0.5 s.

### Action Taken When the DTC Sets

DTCs P0642 00, P0643 00, P0652 00, and P0653 00 are Type A DTCs.

### Conditions for Clearing the DTC

DTCs P0642 00 P0643 00, P0652 00, and P0653 00 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

#### 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 P0642 00, P0643 00, P0652 00, and P0653 00 should not set on this ignition cycle.
2. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector for the appropriate sensor 5-volt reference DTC circuit being diagnosed:

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

• | 5-Volt Reference 1-B74 Manifold Absolute Pressure (MAP) Sensor

• | 5-Volt Reference 1-B25B Clutch Pedal Position (CPP) Sensor

• | 5-Volt Reference 1-B1 Air Conditioning (A/C) Refrigerant Pressure Sensor

• | 5-Volt Reference 1-B150 Fuel Tank Pressure (FTP) Sensor

• | 5-Volt Reference 2-B26 Crankshaft Position Sensor

2. Ignition ON, measure for 4.8-5.2 V between each of the 5-volt reference circuits and ground at the following component terminals:

• | B74 Manifold Absolute Pressure (MAP) Sensor circuit terminal C (X1)

• | B25B Clutch Pedal Position (CPP) Sensor circuit terminal C (X1)

• | B1 Air Conditioning (A/C) Refrigerant Pressure Sensor circuit terminal 1 (X1)

• | B150 Fuel Tank Pressure (FTP) Sensor circuit terminal 3 (X1)

• | B26 Crankshaft Position Sensor circuit terminal 3 (X1)

⇒ | 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 K20 Engine Control Module (ECM).

⇒ | 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 K20 Engine Control Module (ECM).

3. Connect each component associated with the 5-volt reference circuit, one at a time, while monitoring the voltage. Verify the voltage remains between 4.8-5.2 V.

⇒ | If the voltage display is not within the specified range when a component is connected, test the signal circuit for a short to voltage. If all circuits test normal, replace the appropriate component.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Manifold Absolute Pressure Sensor Replacement

• | Clutch Pedal Position Sensor Replacement

• | Crankshaft Position Sensor Replacement

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

• | LINK (Fuel Tank Pressure (FTP) Sensor Replacement)

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