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 inside rearview mirror (ISRVM) applies 5 volts to the ambient air temperature sensor. The ambient air temperature sensor is a thermistor which varies in resistance as the temperature changes. As the resistance of the ambient air temperature sensor increases, the ISRVM senses a larger voltage drop across the sensor, indicating a lower temperature. As the resistance of the ambient air temperature sensor decreases, the ISRVM senses a smaller voltage drop across the sensor, indicating a higher temperature.

### Diagnostic Aids

The following table will be used to measure the resistance of the sensor and compare it with the actual ambient temperature. The mirror's temperature accuracy should be within 5 degrees of the actual temperature. The actual temperature should not be taken from a radio station, a sign displaying the temperature, etc. A temperature measuring tool such as a thermometer should be used. Some temperature measuring tools may be within 5 degrees of the actual temperature. Make sure to consult the manufacturer for the accuracy of the tool. This comparison can make the mirror seem off by 5-10 degrees of the actual temperature when it is not.

#### Ambient Air Temperature Sensor Resistance

°C | °F | Minimum Resistance K Ohms | Maximum Resistance K Ohms
--- | --- | --- | ---
-35 | -31 | 234.81 | 250.59
-30 | -22 | 171.69 | 182.31
-25 | -13 | 126.82 | 133.99
-20 | -4 | 94.63 | 99.49
-15 | 5 | 71.30 | 74.58
-10 | 14 | 54.21 | 56.43
-5 | 23 | 41.48 | 43.17
0 | 32 | 32.00 | 33.31
5 | 41 | 24.96 | 25.83
10 | 50 | 19.61 | 20.19
15 | 59 | 15.49 | 15.94
20 | 68 | 12.31 | 12.67
25 | 77 | 9.85 | 10.12
30 | 86 | 7.96 | 8.15
35 | 95 | 6.45 | 6.61
40 | 104 | 5.27 | 5.39
45 | 113 | 4.32 | 4.42
50 | 122 | 3.56 | 3.64
55 | 131 | 2.95 | 3.02
60 | 140 | 2.46 | 2.52

### 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 Testing

1. Ignition OFF, disconnect the ambient air temperature sensor.
2. Ignition OFF, test for less than 1 ohm between the low reference circuit terminal B and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal replace the ISRVM.

3. Ignition ON, verify that OC is displayed on the ISRVM display.

⇒ | If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal replace the ISRVM.

4. Ignition ON, install a 3-amp fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify that SC is displayed on the ISRVM display.

⇒ | If not the specified value, test the signal circuit for an open/high resistance. If the circuit tests normal replace the ISRVM.

5. If all circuits test normal, replace the ambient air temperature sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Control Module References for ISRVM replacement, setup, and programming

• | Ambient Air Temperature Sensor Replacement