Ambient Temperature Sensor / Switch HVAC: Testing and Inspection

The temperature function is supported by the ambient temperature sensor, a wiring circuit, and a portion of the A/C-heater control. If any portion of the ambient temperature sensor circuit fails or if PCI Bus information is missing, a (- -) will appear in the display in place of the temperature. When the sensor is exposed to temperatures above 55° C (130° F), or if the sensor circuit is shorted, 55° C (130° F) will appear in the display in place of the temperature, when the sensor is exposed to temperatures below -40° C (-40° F) or if the sensor circuit is open, -40° C (-40° F) will appear in the display.

The ambient temperature sensor circuit can also be diagnosed using the following Sensor Test, and Sensor Circuit Test. If the temperature sensor and circuit are confirmed to be OK, but the temperature display is inoperative or incorrect, test the mini-trip computer.

SENSOR TEST
1. Turn the ignition switch to the Off position. Disconnect and isolate the battery negative cable. Disconnect the ambient temperature sensor harness connector.
2. Measure the resistance of the ambient temperature sensor. At - 40° C (- 40° F), the sensor resistance is 336 kiloohms. At 55° C (130° F), the sensor resistance is 2.488 kiloohms. The sensor resistance should read between these two values. If OK, refer to Sensor Circuit Test. If not OK, replace the faulty ambient temperature sensor.

SENSOR CIRCUIT TEST
1. Turn the ignition switch to the Off position. Disconnect and isolate the battery negative cable. Disconnect the wire harness connectors from the ambient temperature sensor and theA/C-heater control.
2. Connect a jumper wire between the two terminals in the body half of the ambient temperature sensor harness connector.
3. Check for continuity between the sensor return circuit and the ambient temperature sensor signal circuit cavities of the A/C-heater control harness connector. There should be continuity. If OK, go to Step 4. If not OK, repair the open sensor return circuit or ambient temperature sensor signal circuit to the ambient temperature sensor as required.
4. Check for continuity between the ambient temperature sensor signal circuit cavity of the A/C-heater control harness connector and a good ground. There should be no continuity. If OK, test the mini-trip computer. If not OK, repair the shorted ambient temperature sensor signal circuit as required.