Ambient Temperature Indicator

An ambient temperature indicator is optional equipment on all instrument clusters. In vehicles so equipped, the ambient temperature indication can be toggled with the clock indication on the right side of the multi-function indicator Liquid Crystal Display (LCD) located near the lower edge of the instrument cluster, directly below the speedometer. The ambient temperature indication consists of a numeric value with a "+" (plus) or "2" (minus) prefix, and the unit of measure is identified with the characters "�C" (Canadian vehicles only) or "�F" (United States vehicles only) located directly above the temperature indication. The indications of the ambient temperature indicator are not visible when the LCD is not illuminated. When illuminated the indications appear as dark characters and icons silhouetted against an amber field. When the exterior lighting is turned Off, the display is illuminated at maximum brightness. When the exterior lighting is turned On the display illumination level can be adjusted in concert with the cluster general illumination lighting using the "+" (plus) and "2" (minus) multi-function indicator push buttons. The ambient temperature indicator is serviced as a unit with the instrument cluster.

The optional 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 a hard wired input received by the cluster from the ambient temperature sensor. The ambient temperature indicator is completely controlled by the instrument cluster logic circuit, and that logic will allow this indicator to operate whenever the multi-function indicator Liquid Crystal Display (LCD) is activated. Therefore, the ambient temperature indicator remains functional regardless of the ignition switch position.

The vehicle operator can choose to have the ambient temperature indicator displayed instead of the clock information, but the clock and ambient temperature indicator cannot be displayed at the same time. The clock or ambient temperature indicator display option is selected using the multi-function indicator clock switch on the instrument cluster circuit board. This switch is actuated manually by depressing the clock switch push button that extends through the lower edge of the cluster lens below the left end of the multi-function indicator. Actuating this switch momentarily will toggle the display between the clock and ambient temperature indicator modes. Actuating this switch twice within about one second will cause the display to toggle, but then automatically revert to the originally selected mode after about twenty seconds.

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 instrument cluster continually monitors the resistance through the sensor to determine the temperature value to be displayed. The current value is displayed immediately after the LCD 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 the sensor resistance (temperature falling) regardless of vehicle speed are displayed subject to a sixty second delay.

The ambient temperature sensor is connected to the instrument cluster in series between the ambient temperature sensor return and sense circuits. The ambient temperature sensor and the return and sense circuits to the instrument cluster can be diagnosed using conventional diagnostic tools and methods. For proper diagnosis of the instrument cluster circuitry that controls the ambient temperature indicator, a DRBIII(R) scan tool is required. Refer to the appropriate diagnostic information.