Operation

OPERATION

The ambient temperature indicator gives an indication to the vehicle operator of the outside air temperature. This indicator is controlled by the instrument cluster microprocessor based upon cluster programming and electronic ambient temperature messages received by the cluster over the Controller Area Network (CAN) data bus from the Body Control Module (BCM) (also known as the Signal Acquisition and Actuation Module/SAM).

The ambient temperature indicator is completely controlled by the instrument cluster logic circuit, and that logic will allow this indicator to operate whenever the cluster multi-function indicator display unit is active. Therefore, the ambient temperature indicator remains functional regardless of the ignition switch position. The vehicle operator can choose to have a digital speedometer information displayed instead of the ambient temperature indicator, but the digital speedometer and ambient temperature indicator cannot be displayed at the same time.

On vehicles without the optional steering wheel buttons, the digital speedometer or ambient temperature indicator display option is selected using the multi-function indicator M (Mode) switch on the instrument cluster circuit board. This switch is actuated manually by depressing the push button that extends through the left edge of the cluster lens outboard of the analog speedometer. Actuating this switch for more than one second will toggle the display between the ambient temperature indicator and the digital speedometer modes. On vehicles with the optional steering wheel buttons, the digital speedometer or ambient temperature indicator display option is selected using the multi-function indicator MENU switches on the steering wheel.

The ambient temperature sensor located below the front bumper is a Negative Temperature Coefficient (NTC) thermistor. The internal resistance of the sensor is reduced as the ambient temperature rises. The BCM continually monitors the resistance through the sensor to determine the temperature value to be displayed. The current value is displayed immediately after the display unit is activated. The display value will remain static regardless of decreases in the sensor resistance (temperature rising) below vehicle speeds of 10 to 15 kilometers-per-hour (6 to 9 miles-per-hour). Decreases in the sensor resistance above 15 kilometers-per-hour (9 miles-per-hour) and increases in the sensor resistance (temperature falling) regardless of vehicle speed are displayed subject to a sixty second delay.

For proper diagnosis of the ambient temperature sensor and circuits, the BCM, the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN or KOMBI), the CAN data bus or the electronic communication related to ambient temperature indicator operation, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.