Seat Position Sensor Verification

Seat Position Sensor Description and Operation

Fig 1: Seat Position Sensor

Courtesy of GENERAL MOTORS COMPANY

The seat position sensor is used to determine the proximity of a front passenger seat position with respect to the front air bags. The seat position sensor interfaces with the inflatable restraint sensing and diagnostic module (SDM). The state of the seat position sensor allows the inflatable restraint sensing and diagnostic module to disable stage 2 of the front air bag for a front seat that is forward of the forward/rearward point in the seat track travel. The seat position sensor is a hall effect sensor that is mounted on the outboard seat track of the front seat. The seat track includes a metal bracket that shunts the seat position sensor magnetic circuit creating 2 states of seat position, the shunted state represents a rearward seat position and the non-shunted state represents a forward position. The seat position sensor provides 2 current ranges, one range for the shunted state and a second range for a non-shunted state which are inputs to the inflatable restraint sensing and diagnostic module. When the inflatable restraint sensing and diagnostic module receives input from a seat position sensor that state 1 threshold is reached (seat is rearward), the inflatable restraint sensing and diagnostic module will enable stage 2 deployment. When state 2 threshold is reached (seat is forward), the inflatable restraint sensing and diagnostic module will disable stage 2 deployment on the side the seat is forward. An improper air gap will form if the sensor is not mounted properly, the bracket the sensor is mounted on is damaged, or the metal track the sensor detects is damaged. As shown above, the Seat Position Sensor (1) and the metal track must be parallel in order to create the proper air gap.

Seat Position Sensor Verification

If the seat position sensor was removed and reinstalled, the sensors mounting bolt loosened, or a wiring repair was performed, use the following procedure to verify the Seat Position Sensor functions properly.

1. Monitor the appropriate data parameter in the SDM Data  list:
   • Driver Seat Position Sensor
   • Passenger Seat Position Sensor
2. Move the appropriate seat to the most forward position and then move it to the most rearward position and verify the status changes.
   • If the status does not change 
   1. Verify there are no circuit DTC's set in the SDM. If DTC's are present resolve them prior to continuing with this verification.
   2. Physically remove the sensor with the electrical connector still attached to the sensor. Turn the Ignition ON/Vehicle in Service Mode.
   3. Place the sensor so it is not near any metal and note the status of the Seat Position Sensor scan tool parameter.
   4. Place the face of the sensor (side which attaches to the seat frame) on a piece of metal to verify the status changes.
      • If the status changes, physically inspect the Seat Position Sensor's mounting tab and the steel track that the sensor aligns with to ensure the sensor and track are parallel with each other. If they are not parallel or there is damage to the bracket or track that would cause an excessive air gap between the sensor and the steel plate. Correct this issue to ensure proper Seat Position Sensor function.
      • If the status does not change, replace the Seat Position Sensor.
   • If the status changes 
3. All OK.