For 1990-2009 cars

### 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 rear view mirror uses 2 photocell sensors that detects an increase in light. One sensor is located in the rear side of the mirror. This sensor determines the light condition present at the mirror face. The other sensor is the ambient light sensor, located on the front of the mirror or windshield side. This sensor determines the amount of light present at the mirror, When the ambient light sensor senses a low light condition and a high light condition from behind at the headlight sensor, the inside rearview mirror will automatically darken the face of the mirror.

### Diagnostic Aids

The automatic day-night feature of the inside rearview mirror may mot operate properly or become inoperative due to a short to battery positive voltage in the backup lighting system.

### Reference Information

#### Schematic Reference

Inside Rearview Mirror Schematics

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Verification

Ignition ON, place the gear shifter into the drive position, cover the ambient light sensor that faces the front windshield. Shine a flashlight into the rearview mirror face. The face of the mirror should darken.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the rearview mirror.
2. Test for less than 1 ohm of resistance between the ground circuit and ground.

⇒ | If greater than 1 ohm, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between the voltage supply circuit and ground.

⇒ | If the test lamp does not illuminate, repair the voltage supply circuit for a short to ground or an open/high resistance.

4. With the transmission in PARK, test for less than 0.5 volts between the backup lamp supply voltage circuit and ground.

⇒ | If the voltage is greater than 0.6 volt, test the backup lamp supply voltage circuit for a short to voltage.

5. With the transmission in REVERSE, test for greater than 11 volts between the backup lamp supply voltage circuit and ground.

⇒ | If the voltage is not 12 volts, test the backup lamp supply voltage circuit for an open/high resistance.

6. If all circuits test normal, replace the rearview mirror.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Inside Rearview Mirror Replacement

• | Control Module References for BCM replacement, setup, and programming.