Theory Of Operation

The ambient air temperature sensor is a Negative Temperature Coefficient (NTC) thermistor that when the temperature increases the resistance decreases. The Body Control Module (BCM) uses an internal 10k ohm pull up resistor and provides a 5-volt reference that it uses as an analog signal with the ambient air temperature sensor. The ambient air temperature sensor is directly connected to the BCM. The BCM receives the signal from the sensor, it sends the filtered values on both the CAN-C and CAN-IHS with 1 degree increments to the Instrument Panel Cluster (IPC) and Radio for the driver display. The BCM also sends filtered values of 0.01 degree increments on both the CAN-C and CAN-IHS.

The ambient temperature sensor filtering is further determined by the ignition off duration, engine run status, engine coolant temperature, and vehicle speed. The information is then used for the following modes - Slow, Fast and Instant. The slow filtered results are used when heat soaking is likely to take place from sources like direct sun radiating on the sensor, heat radiating from the hot surfaces near the sensor or far from the sensor and air convection (warm air coming from the engine compartment of the vehicle itself or from adjacent vehicles) with an engine off timer less than 60 minutes. The fast filtered results are used when heat soaking has some effect on the sensor reading with an engine off timer greater than 60 minutes. The instant filtered results are used when heat soaking conditions are not likely and do not take place during slow or fast modes.