Circuit/System Description

The outside air temperature sensor is a variable resistor interfaced to the body control module (BCM). The BCM monitors the outside air temperature sensor. The outside air temperature sensor is a 2-wire negative temperature coefficient thermistor. The BCM applies 5 volts to an internal input resistor connected to the signal circuit of the outside air temperature sensor. The BCM also provides the ground to the outside air temperature sensor through the low reference circuit. When the outside air temperature is cold, the sensor resistance is high and the signal voltage is high. When the out side air temperature is hot, the sensor resistance is low and the voltage signal is low. The BCM provides the logic for reading the sensor, filtering the data and transmitting this information via the GM LAN low speed bus to the driver information center (DIC) for display. The temperature is sent to the IPC in degrees celsius. The IPC is responsible for displaying the temperature and converting to degrees fahrenheit if necessary. Two GM LAN low speed bus signals are ultimately generated. An unfiltered value and a filtered value for use by the DIC display. The BCM also provides the sensor out-of-range detection and compensates for engine temperature by utilizing vehicle speed and engine off time duration. The algorithm for all messages is executed at a rate of once every 1 second.