Diagnostic Instructions

DTC Descriptors

DTC P0641: 5-Volt Reference 1 Circuit

DTC P0642: 5-Volt Reference 1 Low Voltage

DTC P0643: 5-Volt Reference 1 High Voltage

DTC P0651: 5-Volt Reference 2 Circuit

DTC P0652: 5-Volt Reference 2 Low Voltage

DTC P0653: 5-Volt Reference 2 High Voltage

DTC P0697: 5-Volt Reference 3 Circuit

DTC P0698: 5-Volt Reference 3 Low Voltage

DTC P0699: 5-Volt Reference 3 High Voltage

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage
Accelerator Pedal Position (APP) Sensor 1 5-Volt Reference 2 Circuit	P0652	P2122	P0653
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference 3 Circuit	P0698	P2127	P0699
Air Conditioning (A/C) Refrigerant Pressure Sensor 5-Volt Reference 3 Circuit	P0698	P0532	P0699
Brake Booster Vacuum Sensor 5-Volt Reference 3 Circuit	P0698	P0557	P0699
Crankshaft Position Sensor 5-Volt Reference 3 Circuit	P0698	P0335	P0699
Engine Oil Pressure Sensor 5-Volt Reference 3 Circuit	P0698	P0520	P0699
Exhaust Camshaft Position Sensor 1 5-Volt Reference 2 Circuit	P0652	P0365	P0653
Fuel Rail Pressure Sensor 5-Volt Reference 1 Circuit	P0642	P0192	P0643
Intake Camshaft Position Sensor 1 5-Volt Reference 2 Circuit	P0652	P0340	P0653
Manifold Absolute Pressure (MAP) Sensor 5-Volt Reference 1 Circuit	P0642	P0107	P0643
Throttle Position (TP) Sensor 1 5-Volt Reference 3 Circuit	P0698	P0122	P0699
Throttle Position (TP) Sensor 2 5-Volt Reference 3 Circuit	P0698	P0222	P0699
Intake Air Pressure and Temperature Sensor 5-Volt Reference 1 Circuit	P0642	P0238	P0643

Circuit/System Description

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

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

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

The 5-volt reference 3 bus provides 5 volts to the following sensors:

Conditions for Running the DTC

Conditions for Setting the DTC

P0641, P0651, and P0697

These DTCs set when the ECM detects a voltage out of tolerance condition on the 5-volt reference 1, 2 or 3 bus for more than 3 seconds.

P0642, P0652, and P0698

These DTCs set when the ECM detects a low voltage condition on the 5-volt reference 1, 2, or 3 bus for more than 3 seconds.

P0643, P0653, and P0699

These DTCs set when the ECM detects a high voltage condition on the 5-volt reference 1, 2, or 3 bus for more than 3 seconds.

Action Taken When the DTC Sets

DTCs P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698, and P0699 are Type A DTCs.

Conditions for Clearing the DTC

DTCs P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698, and P0699 are Type A DTCs.

Diagnostic Aids

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

With the ignition ON and the engine OFF, observe the 5-volt Reference 1, 2, and 3 parameters. The scan tool should display OK for a normally operating system.

Circuit/System Testing

Note: Additional DTCs will set when disconnecting the components.

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

Note: 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 range, test for a short to ground on all the 5-volt reference circuits. If all circuits test normal, replace the K20 ECM.

⇒	If the voltage is greater than the specified range, test for a short to voltage on all the 5-volt reference circuits. If all circuits test normal, replace the K20 ECM.

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 K20 ECM.

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

Repair Instructions

Repair Verification

With the ignition ON and the engine OFF, observe the 5-Volt Reference 1, 2 and 3 parameters. The scan tool should display 5-volt reference circuit status OK for a normally operating system.