The outside air temperature is displayed on the Driver Information Center, radio or rear view mirror in a number of GM vehicles. There may be some confusion about the operation of the display and how quickly it updates ambient temperature. Depending on several factors, the temperature may not be updated immediately and owners may feel that the display is inaccurate at times.
The ambient air temperature sensor is a variable resistor interfaced to the Body Control Module (BCM). The BCM provides the logic for reading the ambient air temperature sensor, filtering the data and transmitting the information via the serial data circuit to the outside temperature display. The outside air temperature algorithm uses three pieces of information: outside air temperature data, vehicle speed, and the time the engine was turned off.
When the engine is first started, the algorithm looks at how long the engine was off and if the outside temperature is lower than the last reading taken during the previous ignition cycle. From this information, it's determined if a new outside temperature reading should be taken.
If the engine was off long enough or the current outside air temperature is cooler than the stored value, a new outside temperature reading is taken and displayed. If the engine was not off long enough or the current outside air temperature is higher than the stored value from the previous ignition cycle, the last stored value of outside air temperature taken will be displayed.
The outside air temperature will continue to be updated every second as long as the outside air temperature is the same or cooler than the previous reading. Once the new outside air temperature reading exceeds the previous temperature and the vehicle is traveling less than 18 mph (29 km/h), the displayed outside air temperature will remain at its last value. Once the vehicle speed exceeds 18 mph, the displayed outside air temperature will be updated. If the speed drops below 18 mph, the outside air temperature will freeze at its last value.
The ambient temperature display may be slow to update the outside temperature at times or the A/C compressor may not operate due to low ambient temperature on some 2008-2012 Enclave; 2009-2012 Traverse; 2007-2010 OUTLOOK; 2007-2012 Acadia, Escalade, Escalade ESV, Escalade EXT, Avalanche, Silverado, Suburban, Tahoe, Sierra, Yukon, Yukon Denali, Yukon XL, and Yukon Denali XL models.
The outside air temperature display utilizes a very specific filtering routine of the Ambient Temperature Sensor signal so the display will update gradually without making large jumps in the reading. This is designed to eliminate the possibility of erratic readings under certain driving conditions.
The temperature display is always allowed to update quickly when the ambient temperature is getting colder while driving, but the display takes much longer to update when the temperature is getting warmer. This prevents false updates to the temperature display while driving in slow or stop-and-go traffic in hot weather.
The temperature display will always read the actual ambient temperature when the vehicle is started if the temperature has dropped since the last key cycle. It will not immediately update to the actual ambient temperature if it has gotten warmer since the last key cycle unless the ignition has been off for at least 2.5 hours.
