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 P0642: 5-Volt Reference 1 Circuit Low Voltage

DTC P0643: 5-Volt Reference 1 Circuit High Voltage

Diagnostic Fault Information

Circuit

Short to Ground

High Resistance

Open

Short to Voltage

Signal Performance

APP Sensor 1 - 5-Volt Reference

P0237, P0340, P0462, P0522, P0642, P2067, P2122, P2454, P2564

P2138

P2122

P0238, P0340, P0401, P0463, P0523, P0643, P2068, P2455, P2565

--

Boost Sensor - 5-Volt Reference

P0237, P0340, P0462, P0522, P0642, P2067, P2122, P2454, P2564

P0101

P0237

P0238, P0340, P0401, P0463, P0523, P0643, P2068, P2455, P2565

--

TC Vane Position Sensor - 5-Volt Reference

P0237, P0340, P0462, P0522, P0642, P2067, P2122, P2454, P2564

P2563

P2564

P0238, P0340, P0401, P0463, P0523, P0643, P2068, P2455, P2565

--

EGR Valve - 5-Volt Reference

P0237, P0340, P0462, P0522, P0642, P2067, P2122, P2454, P2564

P046C

P0405

P0238, P0340, P0401, P0463, P0523, P0643, P2068, P2455, P2565

--

Camshaft 4 X - 5-Volt Reference

P0237, P0340, P0462, P0522, P0642, P2067, P2122, P2454, P2564

P0340

P0340

P0238, P0340, P0401, P0463, P0523, P0643, P2068, P2455, P2565

--

Intake Air Flow Valve

P0237, P0340, P0462, P0522, P0642, P2067, P2122, P2454, P2564

P02E7

P02E8

P0238, P0340, P0401, P0463, P0523, P0643, P2068, P2455, P2565

--

Fuel Tank Level Sensor 1 and 2

P0237, P0340, P0462, P0522, P0642, P2067, P2122, P2454, P2564

P2068

P2068

P0238, P0340, P0401, P0463, P0523, P0643, P2068, P2455, P2565

--

Oil Pressure Sensor - 5-Volt Reference

P0237, P0340, P0462, P0522, P0642, P2067, P2122, P2454, P2564

P0522

P0522

P0238, P0340, P0401, P0463, P0523, P0643, P2068, P2455, P2565

--

Fuel Rail Pressure Sensor 5-Volt Reference

P0237, P0340, P0462, P0522, P0642, P2067, P2122, P2454, P2564

P0087, P0192

P0193

P0238, P0340, P0401, P0463, P0523, P0643, P2068, P2455, P2565

--

DPF Differential Pressure Sensor

P0237, P0340, P0462, P0522, P0642, P2067, P2122, P2454, P2564

P2453, P244B

P2454

P0238, P0340, P0401, P0463, P0523, P0643, P2068, P2455, P2565

--

PTO Accelerator Position Sensor 5-Volt Reference

--

--

--

--

--

Circuit/System Description

The engine control module (ECM) supplies 5 volts to components through 5-volt reference circuits. These 5-volt reference circuits are independent of each other outside the ECM, but are bussed together in three reference groups inside the ECM. Therefore, a circuit condition on one sensor 5-volt reference circuit may affect multiple components. The ECM monitors voltage on the 5-volt reference circuits.

Conditions for Running the DTC

P0642

    • DTC P0643 is not set.
    • The ignition is ON for more than 2 seconds.
    • The battery voltage is between 10-16 volts.

P0643

    • DTC P0642 is not set.
    • The ignition is ON for more than 2 seconds.
    • The battery voltage is between 10-16 volts.

Conditions for Setting the DTC

P0642

The ECM detects the 5-volt reference 1 circuit voltage is less than 4.5 volts.

P0643

The ECM detects the 5-volt reference 1 circuit voltage is more than 5.5 volts.

Action Taken When the DTC Sets

DTC P0642 and P0643 are Type A DTCs.

Conditions for Clearing the MIL/DTC

DTC P0642 and P0643 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

  1. The engine starts and runs.
  2. Observe the 5-Volt Reference 1 Circuit Status parameter with a scan tool. The parameter should display OK.
  3. Engine running, observe the DTC information with a scan tool. DTCs P0642 or P0643 should not set.
  4. 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. Turn OFF the ignition for 30 seconds or until the ECM powers down.
  2. Disconnect the camshaft position (CMP) sensor.
  3. Turn ON the ignition, with engine OFF and measure the voltage from the 5-volt reference circuit of the CMP sensor to a good ground with a DMM.
  4. If the voltage measures 4.7-5.2 volts, replace the camshaft position sensor.
  5. With the DMM still connected to the 5-volt reference circuit, disconnect all other components connected to the 5-volt reference 1, one at a time. Refer to Diagnostic Fault Information.
  6. If voltage changes when one of the above components is disconnected, replace the component. Refer to the appropriate replacement procedure.
  7. Test the 5-volt reference 1 circuits for a short to ground or a short to voltage.
  8. If no problem was found in the 5-volt reference circuit, replace the ECM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Accelerator Pedal Position Sensor Replacement
    •  Camshaft Position Sensor Replacement
    •  Exhaust Gas Recirculation Valve Replacement
    •  Exhaust Pressure Differential Sensor Replacement
    •  Fuel Pressure Sensor Replacement
    •  Manifold Absolute Pressure Sensor Replacement
    •  Turbocharger Vane Position Sensor Replacement
    •  Control Module References for ECM replacement, setup, and programming