Power Seat Control Module: Description and Operation

Fig.3 Memory Heated Seat/Mirror Module (MHSMM) Location:

MEMORY HEATED SEAT/MIRROR MODULE
A Memory Heated Seat/Mirror Module (MHSMM) is used on vehicles that are equipped with the heated seat system option. The module is used to control all of the driver side seat/mirror memory functions and both the driver and passenger heated seat functions. The memory heated seat/mirror module contains a central processing unit and interfaces with the Programmable Communications Interface (PCI) data bus network. Refer to the Heated Seats section of this manual for more information on the heated seat system.

The module is packaged in a black molded plastic case which is mounted under the forward edge of the driver side front seat cushion. This location makes it somewhat difficult to remove because it sits between the power seat track and the seat cushion frame. However, it can be removed without having to remove the drivers seat, refer to the procedure in this section for detailed instructions.

For diagnosis of the MHSMM or the PCI data bus, a DRB III scan tool and the Service/Diagnostic Procedures manual are recommended. The Memory Heated Seat/Mirror Module cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The Memory Heated Seat/Mirror Module controls the heated seat and memory seat, mirror systems. However different, these two systems share some software programmed into the module. Refer to the following text which explains how the two different systems are controlled by the memory heated seat/ mirror module.

HEATED SEAT SYSTEM OPERATION
The Memory Heated Seat/Mirror Module receives hard wired inputs from the heated seat switches and the heated seat sensors located, on each of the front seats. The programmed software in the MHSMM allows it to know the temperature of the seat by a resistance reading generated from the seat cushion element mounted thermistor (Heated Seat Temperature Sensor). When a heated seat switch is depressed the module will power the appropriate heating element until the correct preset temperature is achieved. Refer to heated seat switch, element and sensor descriptions for additional information.

MEMORY SEAT/MIRROR SYSTEM OPERATION
The Memory Heated Seat/Mirror Module receives hard wired inputs from the memory seat switch and the potentiometers, mounted on each of the driver power seat track motors and both side view mirrors. The programmed software in the MHSMM allows it to know where the seat/mirror is located in its designed travel by a resistance reading generated from the seat track or mirror mounted potentiometer. This way when the memory switch is depressed the module will power the seat track or mirror motors until the correct preset location is achieved. The MHSMM will prevent the seat memory recall function from being initiated if the transmission gear selector lever is not in the Park or Neutral positions, or if the vehicle is moving. These inputs are monitored over the PCI data bus circuit.