Outside Air Temperature Display

The Ambient Air Temperature (AAT) sensor provides the ambient air temperature data used for the outside air temperature display in the IPC. The ambient air temperature sensor is hardwired to the PCM through separate input and return circuits. The PCM provides a reference voltage to the ambient air temperature sensor and monitors the change in voltage resulting from changes in resistance as determined by outside air temperature.

The PCM sends the ambient air temperature data to the GWM over the HS-CAN1. The GWM sends the ambient air temperature data to the HVAC module over the MS-CAN. The HVAC module filters the ambient air temperature input and sends the outside air temperature message to the GWM over the MS-CAN. The GWM sends the outside air temperature message to the IPC over the HS-CAN3.

Due to the location of the Ambient Air Temperature (AAT) sensor, it is greatly influenced by heat generated from outside the vehicle. For this reason the outside air temperature value displayed in the IPC does not update quickly in the upward (hotter) direction under 38 km/h (21 mph). This update strategy is used because the PCM is unable to determine whether the increase in temperature is truly from an ambient temperature rise or by heat generated from vehicle heat surrounding the sensor.

The outside air temperature display in the IPC updates in the upward (hotter) direction quicker under the following situations:

if the vehicle is driven (approximately 38 km/h [21 mph]) continuously without the vehicle speed dropping for approximately 90 seconds.
if the vehicle is allowed to sit with the engine off for approximately 3 hours (the outside air temperature display in the IPC immediately updates to reflect the current ambient conditions since the engine has cooled sufficiently and no longer has an effect on the outside air temperature sensor reading).
if the Ambient Air Temperature (AAT) sensor drops below 30 deg. C (86 deg.F).

NOTE: If a warm vehicle is left idling for more than 5 minutes, the outside air temperature display freezes until the vehicle is driven above 38 km/h for a continuous 6 minutes (to remove upheat).

NOTE: The outside air temperature does not update when the engine is at idle.

NOTE: If the vehicle speed drops below the programmed speed (approximately 38 km/h) before the outside air temperature display in the IPC begins to update, the PCM logic resets and the time starts over.

Because this filtering strategy exists, it may be necessary to drive the vehicle continuously (approximately 38 km/h [21 mph]) for approximately 90 seconds when observing the outside air temperature display operation. After the vehicle has been driven (approximately 38 km/h [21 mph]) for 90 seconds, the outside air temperature display in the IPC should start to filter upward toward the actual outside air temperature. Depending on the difference between what the outside air temperature is displaying in the IPC and the actual outside temperature, it can take several minutes for the outside air temperature display in the IPC to reach the actual outside temperature.

The outside air temperature display in the IPC does not filter in the downward (colder) direction and always displays the coldest temperature detected by the sensor even when the vehicle is stationary and idling. When the outside Ambient Air Temperature (AAT) is lower than the temperature displayed in the IPC, the IPC immediately updates the displayed temperature downward to reflect the colder ambient air temperature, even at idle.