RAM 3500 Truck 2WD V10-8.0L VIN W HDC (2000)
Seat Heater Control Module: Description and Operation
Heated Seat Module
HEATED SEAT MODULE
The heated seat module is also known as the Seat Heat Interface Module or SHIM. The heated seat module is located under the front seat center
cushion, where it is secured to a mounting bracket that also serves as the support for the slide-out rear seat cup holder unit. Two of the three
mounting tabs that are molded into the plastic housing of the heated seat module are inserted through two holes in the mounting bracket and then
secured by two push on retainers. The heated seat module has a single connector receptacle that allows the module to be connected to all of the
required inputs and outputs through the seat wire harness.
The heated seat module is an electronic microprocessor controlled device designed and programmed to use inputs from the heated seat relay, the
two heated seat switches and the two heated seat sensors to operate and control the heated seat elements in both front seats and the two heated seat
indicator lamp Light-Emitting Diodes (LEDs) in each heated seat switch. The heated seat module is also programmed to perform self-diagnosis of
certain heated seat system functions and provide feedback of that diagnosis through the heated seat switch indicator lamps.
The heated seat module cannot be repaired. If the heated seat module is damaged or faulty, the entire module must be replaced.
The heated seat module operates on fused battery current received from the heated seat relay. The module is grounded at all times through a
ground screw located below the left rear speaker in the cab of the vehicle. Inputs to the module include a resistor multiplexed heated seat switch
request circuit for each of the two heated seat switches and the heated seat sensor inputs from the seat cushions of each front seat. In response to
those inputs the heated seat module controls battery current feeds to the heated seat elements and sensors, and controls the ground for the heated
seat switch indicator lamps.
When a heated seat switch (Driver or Passenger) request signal is received by the heated seat module, the module energizes the proper indicator
lamp (Low or High) in the switch by grounding the indicator lamp circuit to indicate that the heated seat system is operating. At the same time, the
heated seat module energizes the selected heated seat sensor circuit and the sensor provides the module with an input indicating the surface
temperature of the selected seat cushion.
The Low heat set point is about 36 °C (96.8 °F), and the High heat set point is about 42 °C (107.6 °F). If the seat cushion surface temperature
input is below the temperature set point for the selected temperature setting, the heated seat module energizes an N-channel Field Effect Transistor
(N-FET) within the module which energizes the heated seat elements in the selected seat cushion and back. When the sensor input to the module
indicates the correct temperature set point has been achieved, the module de-energizes the N-FET which de-energizes 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 heated seat module detects a heated seat sensor value input that is out of range or a shorted or open heated seat element circuit, it will notify
the vehicle operator or the repair technician of this condition by flashing the High and/or Low indicator lamps in the affected heated seat switch.
Refer to Heated Seat System and Heated Seat Module diagnosis and testing procedures.
