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.

Circuit/System Description

The automatic day/night feature of the driver outside rearview mirror is controlled by the inside rearview mirror. The inside rearview mirror supplies a signal and a low reference to the driver outside rearview mirror. The voltage on the signal circuit of the driver outside rearview mirror varies between 0.5-1.5 volts depending on light conditions present at the inside rearview mirror. At night, with the automatic day-night feature enabled, the driver outside rearview mirror will automatically darken with the inside rearview mirror to reduce the glare from the headlamps from behind. The voltage on the signal circuit of the driver outside rearview mirror will be near 1.5 volts. In daytime conditions, the mirrors are in the normal state. The voltage on the signal circuit of the driver outside rearview mirror may be less than or near 0.5 volts. For more detailed information concerning automatic day night mirror operation refer to Automatic Day-Night Mirror Description and Operation .

Reference Information

Schematic Reference

    •  Inside Rearview Mirror Schematics
    •  Outside Rearview Mirror Schematics

Connector End View Reference

Mirror Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data Definitions
    •  Scan Tool Data List
    •  Scan Tool Output Controls

Circuit/System Testing

  1. Ignition OFF, disconnect the C3 harness connector at the driver outside rearview mirror.
  2. Ignition OFF, test for less than 1.0 ohm of resistance between the low reference circuit terminal 1 and ground.
  3. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the inside rearview mirror.
  4. Ignition ON, test for 0.5-1.5 volts between the signal circuit terminal 2 and ground.
  5. If less than the specified range, test the signal circuit terminal 2 for a short to ground or an open/high resistance. If the circuit tests normal, replace the inside rearview mirror.
    If greater than the specified range, test the signal circuit terminal 2 for a short to voltage. If the circuit tests normal, replace the inside rearview mirror.
  6. If all circuits test normal, test or replace the driver outside rearview mirror.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Inside Rearview Mirror Replacement
    •  Power Mirror Replacement