Temperature Sensors

When the vehicle operator determines what temperature is desired, the automatic system uses multiple sensors to achieve and maintain the desired temperature. The HVAC control module software receives an input of the inside air temperature from the inside air temperature sensor. A 5-volt reference signal is sent from the HVAC control module to the inside air temperature sensor over the inside air temperature sensor signal circuit. A thermistor inside the sensor varies the voltage. That varied voltage provides a signal to the software inside the HVAC control module. As the air temperature increases, resistance decreases. Remaining voltage from the inside air temperature sensor is sent back to the HVAC control module ground through the low reference circuit.

The ambient air temperature sensor provides the HVAC control module software with the temperature outside the vehicle and displays that temperature on the HVAC control module. A 5-volt reference signal is sent from the HVAC control module to the ambient air temperature sensor over the outside air temperature sensor signal circuit. A thermistor inside the sensor varies the voltage. That varied voltage provides a signal to the software inside the HVAC control module. As the air temperature increases, resistance decreases. Remaining voltage from the ambient air temperature sensor is sent back to the HVAC control module ground through the low reference circuit.

Since the sensor is mounted in the front grille area under the front bumper and can be affected by city traffic, idling, and hot engine restarts, the ambient air temperature sensor could give a false temperature reading. If the ambient air temperature increases, the VF display will not update until the vehicle is driven at speeds greater than 32 km/h (20 mph), for one and a half minutes. The digital display will update sooner if the vehicle is driven at speeds greater than 72 km/h (45 mph), for one minute. If the sensor reading is ever cooler than the displayed value, then the ambient air temperature changes are displayed as rapidly as possible.

If the vehicle has been turned off for more than 3 hours, the current outside temperature will be shown when you start the vehicle. If it has been turned off for less than 3 hours, the temperature will be recalled from the previous ignition cycle.

If a malfunction should occur in either the inside or ambient air temperature sensor circuits, the HVAC control module will set a DTC code. The HVAC control module will also substitute a temperature value of 24°C (75°F) if the inside air temperature sensor has a failure. If the ambient air temperature sensor fails, a temperature of 9°C (49°F) will be substituted by the HVAC control module. These substitute temperatures allow the HVAC control module to continue operation.