Road Temperature Sensor: Description and Operation

AMBIENT TEMP SENSOR
Ambient air temperature is monitored by the overhead console through ambient temperature messages received from the Front Control Module (FCM) over the Programmable Communications Interface (PCI) J1850 data bus circuit. The FCM receives a hard wired input from the ambient temperature sensor. The ambient temperature sensor is a variable resistor mounted to a bracket that is secured with a screw to the right side of the headlamp mounting module grille opening, behind the radiator grille and in front of the engine compartment.

Refer to Front Control Module in Electronic Control Modules. For complete circuit diagrams, refer to the appropriate wiring information. The ambient temperature sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The ambient temperature sensor is a variable resistor that operates on a five-volt reference signal sent to it by the Front Control Module. The resistance in the sensor changes as temperature changes, changing the temperature sensor signal circuit voltage to the Front Control Module. Based upon the resistance in the sensor, the Front Control Module senses a specific voltage on the temperature sensor signal circuit, which it is programmed to correspond to a specific temperature. The Front Control Module then sends the proper ambient temperature messages to the EVIC, CMTC over the PCI J1850 data bus.

The thermometer function is supported by the ambient temperature sensor, a wiring circuit, the Front Control Module, the Programmable Communications Interface (PCI) data bus, and a portion of the Electronics module. If any portion of the ambient temperature sensor circuit fails, the Front Control Module will self-diagnose the circuit.

The ambient temperature sensor circuit can also be diagnosed by referring to Diagnosis and Testing - Ambient Temperature Sensor, and Diagnosis and Testing - Ambient Temperature Sensor Circuit. If the temperature sensor and circuit are confirmed to be OK, but the temperature display is inoperative or incorrect, refer to Diagnosis and Testing - Overhead Console in this group. For complete circuit diagrams, refer to the appropriate wiring information.