Heated Seat System: Notes

Individually controlled driver and passenger side electrically heated front seats are available factory-installed optional equipment. The heated seat system allows both the driver and the front seat passenger the option to select one of 2 seat heating ranges, low or high, or to turn the individual seat heaters off using the heated seat switches located in the outboard sides of the seat cushion side shields. The heated seat switch circuit operates on ignition switched battery current supplied through a fuse in the junction block, only when the ignition switch is in the on position.

The heated seat options includes the following:

• Heated Seat Module (HSM) or Memory Heated Seat/Mirror Module (MHSMM)
• Heated seat switch
• Heated seat elements and sensors

The heated seat system also relies upon resources shared with other electronic modules in the vehicle over the PCI data bus network. The PCI data bus network allows the sharing of sensor information. This helps to reduce wire harness complexity, internal controller hardware and component sensor current loads. At the same time, this system provides increased reliability, enhanced diagnostics and allows the addition of many new feature capabilities.

The heated seat system will only operate when the ignition switch is in the on position and the surface temperature at the front seat heating element sensors is below the designed temperature set points of the system. The heated seat system will not operate in ambient temperatures greater than 105°F (41°C). The front seat heating elements and sensors are hard wired to the Heated Seat Module (HSM) or the MHSMM.

The heated seat switches are hard wired to the BCM. The BCM monitors the heated seat switch inputs, then sends heated seat switch status messages to the HSM/MHSMM over the PCI data bus. The HSM/MHSMM contains the control logic for the heated seat system. The HSM/MHSMM responds to the heated seat switch status messages, ignition switch status messages and the front seat heating elements through integral solid-state relays.

When a seat heater is turned on, the sensor located on the seat cushion electric heater element provides the HSM/MHSMM with an input indicating the surface temperature of the seat cushion. If the surface temperature input is below the temperature set point for the selected Low or High heated seat switch position, the HSM/MHSMM energizes the integral solid-state relay, which supplies battery current to the heating elements in the seat cushion and back. When the sensor input indicates the correct temperature set point has been achieved, the HSM/MHSMM de-energizes the solid-state relay. The HSM/MHSMM will continue to cycle the solid-state relay as needed to maintain the temperature set point.

The HSM/MHSMM and the seat heater elements operate on non-switched battery current supplied through the power seat circuit breaker in the junction block. However, the HSM/MHSMM will automatically turn off the heating elements if it detects an open in the sensor circuit, a short in the heating element circuit causing an excessive current draw, or when the ignition switch is turned to the OFF position.