Grand Cherokee 2WD V8-4.7L VIN J (2004)
Ambient Temperature Sensor / Switch HVAC: Description and Operation
Ambient Temperature Sensor
Ambient air temperature is monitored by the Electronic Vehicle Information Center (EVIC) through ambient temperature messages received from the
Body Control Module (BCM) over the Programmable Communications Interface (PCI) data bus network. The BCM 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 Body 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 BCM. The resistance in the sensor
changes as temperature changes, changing the temperature sensor signal circuit voltage to the BCM. Based upon the resistance in the sensor, the BCM
senses a specific voltage on the temperature sensor signal circuit, which it is programmed to correspond to a specific temperature. The BCM then sends
the proper ambient temperature messages to the EVIC over the PCI data bus.
The temperature function is supported by the ambient temperature sensor, a wiring circuit, the Body Control Module (BCM), the Programmable
Communications Interface (PCI) data bus, and a portion of the Electronic Vehicle Information Center (EVIC) module. If any portion of the ambient
temperature sensor circuit fails, the BCM will self-diagnose the circuit. A temperature reading of 130° F will appear in the EVIC display in place of the
temperature when the sensor circuit is shorted. A temperature reading of -40° F will appear in the EVIC display in place of the temperature when the
sensor circuit is open.
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 - Electronic Vehicle Information Center. For complete circuit diagrams, refer to the appropriate wiring
information.
