Impact Sensor: Description and Operation

Fig.17 Front Impact Sensor:

FRONT IMPACT SENSOR
Two front impact sensors are used on this model, one each for the left and right sides of the vehicle. These sensors are mounted remotely from the impact sensor that is internal to the Airbag Control Module (ACM). Each front sensor is secured with two screws to the backs of the right and left vertical members of the radiator support within the engine compartment. The sensor housing has an integral connector receptacle and two integral mounting points each with a metal sleeve to provide crush protection.

The right and left front impact sensors are identical in construction and calibration with two exceptions:

On models equipped with an optional 2.4L gasoline engine, the left front impact sensor includes a shim that moves the sensor 3 millimeters toward the rear of the vehicle on the left vertical member of the radiator support for additional clearance that is required for that application.

On models equipped with an optional diesel engine, the left front impact sensor includes a stamped metal mounting bracket that rotates the connector receptacle end of the sensor toward the outboard side of the vehicle for additional clearance that is required for that application.

A cavity in the center of the molded black plastic impact sensor housing contains the electronic circuitry of the sensor which includes an electronic communication chip and an electronic impact sensor. Potting material fills the cavity to seal and protect the internal electronic circuitry and components. The front impact sensors are each connected to the vehicle electrical system through a dedicated take out and connector of the headlamp and dash wire harness.

The impact sensors cannot be repaired or adjusted and, if damaged or faulty, they must be replaced. The mounting bracket for the left front impact sensor on models with a diesel engine is serviced as a unit with that sensor.

The front impact sensors are electronic accelerometers that sense the rate of vehicle deceleration and, combined with the ACM Accelerometer and Safing Sensor, provides verification of the direction and severity of an impact. Each sensor also contains an electronic communication chip that allows the unit to communicate the sensor status as well as sensor fault information to the microprocessor in the Airbag Control Module (ACM). The ACM microprocessor continuously monitors all of the front passive restraint system electrical circuits to determine the system readiness. If the ACM detects a monitored system fault, it sets a Diagnostic Trouble Code (DTC) and controls the airbag indicator operation accordingly.

The impact sensors each receive battery current and ground through dedicated left and right sensor plus and minus circuits from the ACM. The impact sensors and the ACM communicate by modulating the voltage in the sensor plus circuit. The hard wired circuits between the front impact sensors and the ACM may be diagnosed and tested using conventional diagnostic tools and procedures. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the ACM or the impact sensors. The most reliable, efficient, and accurate means to diagnose the impact sensors, the ACM, and the electronic message communication between the sensors and the ACM requires the use of a DRB III scan tool. Refer to the appropriate diagnostic information.

CAUTION: DO NOT REMOVE OR INSTALL THE IMPACT SENSORS WHILE THE SENSOR IS CONNECTED TO THE VEHICLE WIRING.