Power Mirror Control Module: Description and Operation

Fig.19 Seat Heat Interface Module:

MEMORY HEATED SEAT/MIRROR MODULE
The heated seat module is also known as the Seat Heat Interface Module or SHIM. The SHIM is located on the power seat track front bracket under the front edge of the right front seat cushion, where it is secured with two push-in type plastic fasteners. The module is contained within a small, rectangular, molded plastic housing and has a single connector receptacle that allows it to be connected to all of the required inputs and outputs through the power seat wire harness.

The SHIM is an electronic microprocessor controlled device that is designed to monitor the inputs and control the outputs of the heated seat system. The SHIM is programmed to provide two levels of heating for each front seat: a Lo temperature set point of about 32 ± (90 °F), or a Hi temperature set point of about 38 °C (100 °F). The SHIM is also programmed to perform self-diagnosis of certain heated seat system functions.

The SHIM cannot be adjusted or repaired. If the SHIM is damaged or faulty, the entire module must be replaced.

The heated seat module (also known as the Seat Heat Interface Module or SHIM) operates on battery current received through a fuse in the Junction Block (JB) on a fused ignition switch output (run-acc) circuit so that the heated seat system will only operate when the ignition switch is in the On or Accessory positions. The SHIM is grounded at all times through a ground feed from a two wire take out and eyelet terminal connector of the power seat wire harness that is secured by a ground screw to the top of the seat crossmember under the right front seat. Inputs to the SHIM include a seat heater switch MUX circuit for each of the two heated seat switches, heated seat sensor inputs from the seat cushions of each front seat, and battery current from the power seat circuit breaker in the JB received through the energized heated seat relay on two heated seat relay output circuits. Outputs from the SHIM include a battery voltage reference to the heated seat sensors on a sensor feed circuit, a battery current feed to the two heated seat element circuits on separate heated seat driver circuits, and separate Lo and Hi driver circuits for each of the heated seat switch Light-Emitting Diode (LED) indicator lamps.

When a driver or passenger heated seat switch request signal is received by the SHIM, the module energizes the proper switch LED indicator lamp (Lo or Hi) by pulling the LED driver circuit to ground. This provides an indication to the vehicle operator that the heated seat system is operating and whether the Hi or Lo heat mode is selected. At the same time, the SHIM energizes the heated seat sensor feed circuit and the sensor provides the module with a heat sense input indicating the surface temperature of the selected seat cushion. If the seat cushion surface temperature input is below the temperature set point for the selected heat mode, the SHIM energizes an N-channel Field Effect Transistor (N-FET) within the module. The N-FET switches battery current to the heated seat elements in the selected seat cushion and back. When the heated seat sensor input indicates the correct temperature set point has been achieved, the SHIM de-energizes the N-FET which switches OFF the battery current to the heated seat elements. The heated seat module will continue to cycle the N-FET as needed to maintain the selected temperature set point.

If the SHIM detects a heated seat sensor value input that is out of range or a shorted or open heated seat element circuit, it will automatically de-energize the N-FET and switch OFF the battery current to the affected heated seat elements. The SHIM will also notify the vehicle operator or the repair technician of this condition by flashing the Hi and/or Lo LED indicator lamps in the affected heated seat switch in a prescribed sequence as a self-diagnostic feedback. Refer to Diagnosis and Testing for the proper heated seat system diagnosis and testing procedures.