For 1990-2009 cars

### Diagnostic Fault Information

Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ambient Air Temperature Sensor Signal Circuit | 2 | 1 | 1 | --
Ambient Air Temperature Sensor Low Reference Circuit | 2 | 1 | 1 | --
Ambient Air Temperature Sensor | 2 | 1 | 1 | --
1. Incorrect Temperature Reading 2. Temperature Displays a SC or OC

### Circuit/System Description

The temperature display, displays the temperature of the surrounding air around the vehicle. The rearview mirror monitors the outside air temperature by monitoring the ambient air temperature sensor. The ambient air temperature sensor is a potentiometer which increases or decreases resistance over the ambient air temperature sensor signal circuit. The amount of voltage that returns to the rearview mirror on the low reference circuit determines what is displayed on the rearview mirror.

### Diagnostic Aids

The following table will be used to measure the resistance to 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, ECT. 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 or the tool. This comparison can make the mirror seem off by 5-10 degrees of the actual temperature when it is not.

Temperature | 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

Instrument Cluster Schematics

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Verification

Ignition ON, observe the temperature display. The temperature reading should be no more than 5 degrees from the actual temperature around the vehicle.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the ambient air temperature sensor.
2. Test for less than 1.0 ohm of resistance between the low reference circuit and ground.

⇒ | If greater than 1.0 ohm, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the inside rearview mirror.

3. Ignition ON, test for 4.8 - 5.2 volts between the 5-volt reference circuit and ground.

⇒ | If less than 4.8 volts, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the inside rearview mirror.

⇒ | If greater than 5.2 volts, tests the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the inside rearview mirror.

4. Install a 3-amp fused jumper wire between the signal circuit and the 5-volt reference circuit. Verify the temperature display is greater than 60°C or 140°F.

⇒ | If less than 60°C or 140°F, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the inside rearview mirror.

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

### Component Testing

1. Ignition OFF, disconnect the harness connector at the ambient air temperature sensor.
2. Measure the resistance of the ambient air temperature sensor from the sensor signal circuit of the low reference circuit. Compare the ambient air temperature sensor resistance reading with the chart above.

⇒ | If the resistance is not within the specified range, replace the ambient air temperature sensor.

### Repair Instructions

Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Ambient Air Temperature Sensor Replacement

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