GM Service Manual Online
For 1990-2009 cars only

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 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

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

P0368

P0653

Fuel Rail Pressure Sensor 5-Volt Reference 1 Circuit

P0642

P0192

P0643

Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit

P0642

P0452

P0643

Intake Camshaft Position Sensor 1 5-Volt Reference 2 Circuit

P0652

P0343

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 manifold absolute pressure (MAP) sensor
    • The clutch apply sensor
    • The fuel rail sensor
    • The fuel tank pressure (FTP) sensor
    • The intake air pressure and temperature sensor

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

    • The accelerator pedal position (APP) sensor 1
    • The exhaust camshaft position (CMP) sensor
    • The intake camshaft position (CMP) sensor

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

    • The APP sensor 2
    • The crankshaft position (CKP) sensor
    • The air conditioning (A/C) refrigerant pressure sensor
    • The throttle position (TP) sensor 1 and 2
    • The brake booster vacuum sensor

Conditions for Running the DTC

    • DTCs P0601, P0602, P0603, P0604, and P0606 are not set.
    • The ignition is in Run, or Crank.
    • The ignition voltage is more than 5.23 volts.
    • DTCs P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698, and P0699 run continuously when the above conditions are met.

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

    • 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

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

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

    Important: Additional DTCs will set when disconnecting the components.

  1. Ignition OFF, disconnect the harness connector of all appropriate sensors for the applicable DTC.
  2. Important: A short to voltage on the signal circuit of certain components may cause this DTC to set.

  3. Ignition ON, measure for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.
  4. 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 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 ECM.
  5. 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.
  6. 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 ECM.
    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
    •  Crankshaft Position Sensor Replacement
    •  Camshaft Position Sensor Replacement - Exhaust
    •  Camshaft Position Sensor Replacement - Intake
    •  Fuel Injection Fuel Rail Fuel Pressure Sensor Replacement
    •  Fuel Tank Pressure Sensor Replacement
    •  Intake Air Pressure and Temperature Sensor Replacement
    •  Manifold Absolute Pressure Sensor Replacement
    •  Throttle Body Assembly Replacement
    •  Diagnostic Trouble Code (DTC) List - Vehicle for ECM replacement, setup, and programming.

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.