Electrically Heated Seats

The heated seat feature is available with or without the memory system. The module is located under the driver's seat and is known as the heated seat module (HSM) or the memory heated seat module (MHSM). The control switches for the heated seats are located on the instrument panel and are wired to the body control module. The BCM then sends the message to the HSM via the PCI bus. The system offers two seat temperature settings of approximately 96.8 F (36°C) (LO) and approximately 107.6 F (41°C) (HI).

As the temperature in the seat rises, the negative temperature coefficient (NTC) resistance decreases and the voltage reading detected by the HSM decreases. The seat heater output is deactivated once the voltage reading reaches it's threshold for either setting, high or low.

As the temperature decreases, the voltage reading increases until the upper threshold is reached for either setting high or low. At this point the seat heat output is activated once again and this cycle repeats itself as long as the seat heat request is on. The thresholds for low and high settings are preprogrammed into the module memory.

The heated seat switch contain resistors pulled up to 5 volts which are processed by the body control module as the voltage readings indicating desired heat setting high or low.

The resistance wire type heater elements inside the seat back and cushion are wired on series. This means that if an element is open there will be no heater output to either the cushion or the seat back.