For 1990-2009 cars

### Heated Seat Components

The heated seats consist of the following components:

• | Left heated seat switch

• | Right heated seat switch

• | Memory seat module

• | Heated seat control module

• | Driver door module

• | Passenger door module

• | Left seat cushion heating element

• | Left seat back heating element

• | Left seat cushion temperature sensor

• | Right seat cushion heating element

• | Right seat back heating element

• | Right seat cushion temperature sensor

### Modes of Operation

The heated seat module (MSM) or the heated seat module (HSM) controls heated seat operation for both the driver and passenger seats. There are 2 modes of operation available for heated seats; both the seat cushion and seat back heat, or seat back only heat. When a heated seat temperature signal request is received, the MSM/HSM will activate both the seat cushion and seat back heating elements. When the heated seat BACK ONLY mode button is pressed once the MSM/HSM will deactivate the seat cushion heating element and leave the seat back heating element ON.

### Heated Seat Switch/LED Indicators and System Operation with A45

The left and right heated seats are controlled by separate heated seat switches. Ground for both heated seat switches is supplied at G302. The driver and passenger door modules control the heated seat switch heat mode and temperature indicators. The memory seat module (MSM) controls the heated seat operation for both the left and right heated seats.

The following describes the sequence of operation and how the MSM responds to each of the switch inputs.

• | High Temperature--When the heated seat switch is pressed once, ground is applied through the switch contacts and the switch signal circuit to the door module indicating the high heat request. In response to this signal, the door module applies a low current voltage through the 3 temperature indicator control circuits illuminating all 3 LEDs indicating the high temperature mode. The module then sends a serial data message to the MSM indicating the heated seat request. The MSM then applies battery voltage through the heating element supply voltage circuit and ground through the element low reference circuits seat cushion and seat back heating elements.

• | Medium Temperature--When the switch is pressed a second time, the MSM sets the temperature level to medium heat. The door module removes the voltage from the high temperature indicator leaving 2 LEDs illuminated indicating the medium temperature mode.

• | Low Temperature--When the switch is pressed a third time, the MSM sets the temperature level to low heat. The door module removes the voltage from the medium temperature indicator leaving 1 LED illuminated indicating the low temperature mode.

• | System OFF State--When the switch is pressed a fourth time, the MSM removes the battery voltage and grounds from the heating elements. The door module removes the voltage from the low temperature indicator, indicating the system OFF state.

• | Back Only Mode-When the heated seat is ON and the BACK ONLY mode button is pressed, ground is applied through the switch contacts and the heated seat back only mode signal circuit to the door module. In response to this signal, the door module sends a serial data message to the MSM indicating the back only mode request. The MSM then opens the ground path to the seat cushion heater element, leaving just the seat back heater active. The door module turns OFF the seat cushion/back mode indicator, then applies a low current voltage through the heated seat back only mode indicator control circuit illuminating the back only mode indicator.

### Heated Seat Switch/LED Indicators and System Operation without A45

Battery voltage is supplied at all times to the heated seat module (HSM) from the HTD/SEAT fuse located in the I/P fuse block. Battery voltage from the BCM is supplied to both heated seat switches with the ignition ON. Ground for both heated seat switches is supplied at G302 while ground for the HSM is supplied at G303.

The following describes the sequence of operation and how the HSM responds to each of the switch inputs.

• | High Temperature--When the heated seat switch is pressed once, ground is applied through the switch contacts and the switch signal circuit to the HSM indicating the high heat request. In response to this signal, the HSM applies battery voltage through the heating element supply voltage circuit and ground through the element low reference circuits to the seat cushion and seat back heating elements. At the same time, the HSM applies a low current voltage through the 3 temperature indicator control circuits illuminating all 3 LEDs indicating the high temperature mode.

• | Medium Temperature--When the switch is pressed a second time, the HSM sets the temperature level to medium heat and removes the voltage from the high temperature indicator leaving 2 LEDs illuminated indicating the medium temperature mode.

• | Low Temperature--When the switch is pressed a third time, the HSM sets the temperature level to low heat and removes the voltage from the medium temperature indicator leaving 1 LED illuminated indicating the low temperature mode.

• | System OFF State--When the switch is pressed a fourth time, the HSM removes the battery voltage and grounds from the heating elements and the voltage from the low temperature indicator, indicating the system OFF state.

• | Back Only Mode-When the heated seat is ON and the BACK ONLY mode button is pressed, ground is applied through the switch contacts and the heated seat back only mode signal circuit to the HSM. In response to this signal, the HSM opens the ground path to the seat cushion heater element, leaving just the seat back heater active. At the same time, the HSM turns OFF the seat cushion/back mode indicator, then applies a low current voltage through the heated seat back only mode indicator control circuit illuminating the back only mode indicator.

### Temperature Regulation

The heated seat system is designed to warm the seat cushion and seat back to approximately 42°C (107.6°F) when in the high position, 39.5°C (103°F) when in the MED position, and 37°C (98.6°F) when in the low position. The memory seat module (MSM)/heated seat module (HSM) monitors the seat temperature through the temperature sensor signal circuits and the temperature sensors (thermistor) that are located in the seat cushion and the seat back. The temperature sensors are variable resistors, their resistance varies as the temperature of the seat changes. When the temperature sensor resistance indicates to the MSM/HSM that the seat has reached the desired temperature, the module opens the ground path of the seat heating elements through the heated seat element control circuit. The module will then cycle the element control circuit open and closed in order to maintain the desired temperature.

### Load Management

The electrical power management function is designed to monitor the vehicle electrical load and determine when the battery is potentially in a high discharge condition. The heated seat system is one of the vehicle loads that is subject to reduction during a battery discharge condition. For more information on load management refer to Electrical Power Management Description and Operation .