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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ignition | 1 | 1 | 1 | --
Backup Lamp Control | 1 | 1 | 1 | --
Ground | -- | 1 | -- | --
1. Inside Electrochromic Mirror Inoperative

### 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.

With the gear selector lever in the REVERSE position, backup lamp control voltage is supplied as an input to the inside rearview mirror. The mirror monitors this input to disable the automatic day-night feature. This allows the driver to see objects in the mirror clearly when backing up, regardless of the rear light sensor status.

### Reference Information

#### Schematic Reference

Inside Rearview Mirror Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Automatic Day-Night Mirror 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 Verification

1. Ignition ON, headlamps ON, vehicle in PARK, cover the front light sensor with a towel or other suitable item. Shine a flashlight at the rear light sensor while observing the inside rearview mirror face. The inside rearview mirror face should dim.
2. Park brake applied, place the transmission in REVERSE. The inside rearview mirror face should transition from dim to bright.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the inside rearview mirror.
2. Test for less than 10 ohms between the low reference circuit terminal 8 and ground.

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

3. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 13 and ground.

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

4. Ignition ON, park brake applied, vehicle in REVERSE, verify that a test lamp illuminates between the backup lamp control circuit terminal 9 and ground.

⇒ | If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, refer to Backup Lamps Malfunction.

5. If all circuits test normal, test or replace the inside rearview mirror.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Inside Rearview Mirror Replacement