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.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Engine Oil Temperature Sensor Signal Circuit

1

1

1

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Engine Oil Temperature Sensor Low Reference Circuit

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1

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1. Engine Oil Temperature Indicator Always On

Circuit/System Description

The engine oil temperature sensor is a thermistor that varies in resistance as the engine oil temperature changes. A low engine oil temperature produces a high resistance at the engine oil temperature sensor. A high engine oil temperature produces a low resistance at the engine oil temperature sensor. The engine control module (ECM) monitors the engine oil temperature sensor via a discreet signal circuit and low reference circuit. The ECM applies 5 volts to the engine oil temperature sensor and calculates temperature based on the engine oil temperature sensor voltage. The engine oil temperature range is between -40°C (-40°F) to -165°C (329°F).

Reference Information

Schematic Reference

Instrument Cluster Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

    •  Instrument Cluster Description and Operation
    •  Indicator/Warning Message Description and Operation

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 Testing

  1. Ignition OFF, disconnect the harness connector at the engine oil temperature sensor.
  2. Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit terminal C and ground.
  3. If greater than the specified range, test the low reference circuit for an open/high resistance.
  4. Ignition ON, verify the scan tool Engine Oil Temperature Calculated parameter is less than -10°C (14°F)
  5. If greater than the specified value, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the ECM.
  6. Ignition ON, install a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal C. Verify the scan tool Engine Oil Temperature Calculated parameter is greater the 150°C (302°F).
  7. If less than the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  8. If all circuits test normal, test or replace the engine oil temperature sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Engine Oil Level Sensor and/or Switch Replacement
    •  Control Module References for the ECM replacement, setup, and programming