Ambient Temperature Sensor / Switch HVAC: Description and Operation

AMBIENT TEMPERATURE SENSOR
The ambient air temperature is monitored by the BCM and displayed by the EVIC. The BCM receives a hardwire input from the Ambient Temperature Sensor (ATS).

The ATS is a variable resistor that operates on a 5 volt reference signal circuit hardwired from the BCM. The resistance in the ATS changes as the outside temperature rises or falls. The BCM senses the change in reference voltage through the ATS resistor. Based on the resistance of the ATS, the BCM is programmed to correspond to a specific temperature. The BCM stores and filters the ambient temperature data and transmits this data to the EVIC via the PCI Bus. The ATS cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

AMBIENT TEMPERATURE SENSOR FAULT CODES
The outside temperature function is supported by the ambient temperature sensor (ATS), a signal and ground circuit hardwired to the BCM, and the EVIC display.

If the EVIC display indicates 54 °C (130 °F) or the ATS sense circuit is shorted to ground, the temp display will be 54 °C (130 °F) to indicate a SHORT circuit condition.

If the EVIC display indicates -40 °C (-40 °F) or the ATS sense circuit is open, the temp display will be -40 °C (-40 °F) to indicate an OPEN circuit condition.

If there is an OPEN or SHORT circuit condition, it must be repaired before the EVIC VFD can be tested.

The ATS is supported by the BCM. Ambient Temperature Sensor DTCs will be recorded in the BCM. The ATS can be diagnosed using the following Sensor Test. Test the ATS circuits using the diagnostics in the Body Diagnostic Procedures Manual. If the EVIC passes the self test, and the ATS, the circuits, and PCI bus communications are confirmed to be OK, but the EVIC temperature display is inoperative or incorrect, replace the BCM.