Principles Of Operation

Seats

Principles of Operation

Power Seats

Each power seat uses a 6-way power seat track and 3 electric motors directly controlled by a seat-mounted, 6-way seat control switch for horizontal (forward/rearward), front height and rear height adjustment.

The power lumbar motor pulls and releases a cable in the lumbar assembly to move the backrest in and out.

The power seat motors are hardwired to the seat control and lumbar switches. The circuits are normally at ground through the seat control switch. An individual motor is switched to voltage and ground when a specific adjustment position is selected. Power seats operate independently from the ignition position.

Heated Seats

The heated seat switches and indicators are part of the Front Controls Interface Module (FCIM). The heated seat system operates independently from the other systems controlled by the FCIM (Front Controls Interface Module) and HVAC module.

When a heated seat button is pressed, the FCIM (Front Controls Interface Module) illuminates the heated seat indicator and transmits a system request message to the HVAC module on the module communication network. The HVAC module receives the message and provides ground to the driver or passenger heated seat relay coil circuit to operate the heated seat. The heated seat system can only operate if both modules are communicating correctly on the communication network and the engine is running.

The driver and passenger heated seat relays are located underneath the driver seat cushion frame. With the ignition ON, voltage is supplied from the Smart Junction Box (SJB) to each heated seat relay coil. Battery voltage is also supplied to the heated seat relay contacts (hot at all times). When energized, the heated seat relay coil closes the relay contact to supply battery voltage from the Battery Junction Box (BJB) to the cushion heater mat. The cushion and backrest heater mats are wired in series and each backrest heater mat is directly connected to ground to complete the electrical circuit to heat a seat.

Each cushion heater mat contains a thermostatic switch that closes when cold to complete the heater grid circuit and heat the seat. When hot, the thermostatic switch opens the heater grid circuit and allows the seat to cool. The heated seat indicator illuminates continuously while the thermostatic switch cycles open and closed. The thermostatic switch is serviceable only as part of a new heater mat.

The HVAC module monitors the heated seat relay coil ground circuits for an open, short to ground and short to voltage. If a circuit fault is detected, a DTC is set and the HVAC module disables the affected seat by removing circuit ground to the heated seat relay coil (refer to the HVAC Module DTC Chart Seats). The HVAC module also transmits a network communication message to the FCIM (Front Controls Interface Module) to deactivate the heated seat indicator. PIDs are available in the FCIM (Front Controls Interface Module) using the scan tool to verify heated seat switch operation.

The seat should be occupied to correctly test for normal operation. Temperature measuring devices do not provide an accurate method for testing heated seat operation as surface temperatures are subject to human and environmental characteristics. Correct testing requires heater mat resistance measurements which have tight tolerances affecting heat cycle time length.

The heated seat system does not time-out and will remain on until selected off or engine is off.