Description And Operation
DESCRIPTION
The Driver Presence Detection Module (DPDM) (1) functions as a back-up sensor used to detect when the driver has entered or exited the vehicle in the absence of the door ajar sensor. It is a modified version of an Occupant Classification Module (OCM), which is a small Electronic Control Unit (ECU) attached by hose to a fluid filled bladder that is located against the bottom surface of the seat foam within the passenger seat structure.
OPERATION
The DPDM is always powered and sending status messages across the Controller Area Network - Chassis (CAN-C) data bus, but is only being monitored when the driver door is removed. The DPDM receives its ignition RUN command status from the Body Control Module (BCM) as well as the vehicle configuration strategy. This strategy is used by the DPDM ECU to select the proper parameter set and calibrations for the vehicle type based on the vehicle line and model year. In most cases, the driver presence message status is used in the same way that the door ajar sensor is used. The DPDM handles the sensor calculations internally to the ECU and transmits a status signal across the CAN-C bus for other ECUs to use. This status signal provides a Faulted/Not Faulted data bit and a status value that is typically one of four values:
- Undetermined (usually used during ECU initialization and calibration)
- Occupied (Driver Present)
- Unoccupied (Seat Empty)
- SNA (Signal Not Available / Loss of Communication)
The status message is updated every 200 milliseconds (ms) on the CAN-C bus.
The DPDM also provides diagnostic data from the internal pressure sensor which is a 0-255 count raw / unfiltered reading. The diagnostic data is also transmitted at a rate of every 50 ms.