For 1990-2009 cars

## Heated/Vented Seat Description and Operation Rear

The rear heated seat system has one control module that controls heat operation for both the left and right rear seat. The rear heated seat consists of the following components:

• | Rear auxiliary HVAC control module

• | Right heated seat switch

• | Left seat cushion heater element

• | Left seat back heater element

• | Left seat cushion temperature sensor

• | Right seat cushion heater element

• | Right seat back heater element

• | Right seat cushion temperature sensor

• | REAR HTD SEATS Fuse 20 A

• | DPM Fuse 10 A

### Power and Grounds

Battery positive voltage is supplied to the rear heated seat module through the ignition 3 voltage circuit and the REAR HTD SEATS Fuse that is located in the left rear fuse block. This voltage is used to power up the heated seat module and to supply power to the seat heater elements This voltage supply allows the heated seat system to operate only with the ignition switch in the ON position. The rear heated seat module is grounded through the module ground circuit and G402.

### Modes of Operation

There is 1 mode available for heated seat operation, both the seat cushion and seat back heat turn on and off together. When a heated seat temperature signal request is received, the heated seat module will activate both the seat cushion and seat back heating elements.

### Heated Seat Switch/LED Indicators and Operation

The left and right rear heated seats are controlled by separate heated seat switches both located in the rear climate control panel (RCCP). Battery positive voltage is supplied to the RCCP by the rear heated seat module. The rear heated seat module controls the heated seat operation for both, the left and right rear heated seats, and the heated seat switch temperature indicators.

The following describes the sequence of operation and how the heated seat module responds to each of the switch inputs.

• | High Temperature: When the heated seat switch is pressed once, battery positive voltage is applied through the switch contacts and the switch signal circuit to the heated seat module indicating the high heat request. In response to this signal, the module applies battery positive through the heating element supply voltage circuits to the seat cushion and seat back heating elements. At the same time, it activates the low side drivers that supply a ground through the heating element control circuits to the seat heating elements. The module then applies a ground through the high temperature indicator control circuit illuminating the high temperature indicator to indicate the high temperature mode.

• | Medium Temperature: When the switch is pressed a second time, the heated seat module sets temperature level to medium heat. Then it removes the ground from the high temperature indicator and applies ground to the medium temperature indicator to indicate the medium temperature mode.

• | Low Temperature: When the switch is pressed a third time, the heated seat module sets the temperature level to low heat. Then it removes the ground from the medium temperature indicator and applies ground to the low temperature indicator to indicate the low temperature mode.

• | System OFF State: When the switch is pressed a fourth time, the heated seat module removes the battery voltage and grounds from the heating elements. Then it removes the ground from the low temperature indicator, indicating the system OFF state.

### 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 heat position, 39.5°C (103.1°F) when in the medium heat position, and 37°C (98.6°F) when in the low heat position. The climate control seat module monitors the seat temperature through the temperature sensor signal circuit and the temperature sensor (thermistor) that is located in the seat cushion. The temperature sensor is a variable resistor, its resistance changes as the temperature of the seat changes. When the temperature sensor resistance indicates to the climate control seat module that the seat has reached the desired temperature, the module turns off the element supply voltage to the seat heating elements. The module will then cycle the element supply voltage on and off in order to maintain the desired temperature.

## Heated/Vented Seat Description and Operation Front

The heated/vented seat system consists of the following components:

• | Heated/Vented Seat Switch

• | Climate Control Seat Module

• | HVAC Control Module

• | Memory Seat Module (MSM)

• | Seat Cushion Heater Element

• | Seat Back Heater Element

• | Temperature Sensor

• | Seat Back Blower Motor

• | Seat Back Blower Motor

• | RF HTD ST/S-BAND Fuse 20 A

• | IGN 3 Fuse 10 A

• | DPM Fuse 10 A

### Helpful Hints

• | The memory seat module (MSM) is also referenced as the driver position module (DPM) for this vehicle.

• | The vented seat is also referenced as the cooled seat for this vehicle.

• | The climate control seat module, located under the front passenger seat cushion, controls the heated and vented seat operations for both the driver and front passenger seats.

### Power and Ground

Battery positive voltage is supplied to the climate control seat module from the IGN 3 Fuse located in the left rear fuse block. This voltage is used to power up the climate control seat module allowing the heated seats to operate only when the ignition switch is in the ON position. Battery positive voltage is also supplied at all times to the climate control seat module from the RF HTD ST/S-BAND fuse located in the right rear fuse block. This voltage is used by the module to supply power to the seat heating elements and is wired directly to the front passenger vented seat blower motors. Battery positive voltage is supplied directly to the driver vented seat blower motors from the DPM fuse located in the left rear fuse block. Ground is provided to the module through the ground circuit and G307.

### Heated/Vented Seat Switch

Separate heated and vented seat switches located in the HVAC control module control the driver and passenger heated/vented seats. When a heated or vented seat switch is pressed, the HVAC control module sends a GMLAN message via the serial data line to the MSM indicating the heated or vented seat command. In response to this signal, the MSM sends a low side PWM signal through the appropriate driver or passenger PWM serial data circuit to the climate control seat module. The module then activates the appropriate heated or vented seat mode The MSM then sends a GMLAN message back to the HVAC module to illuminate the appropriate temperature indicator.

### Heated Seat Operation

When the ignition is turned to the ON position, the heated/vented seats will initialize in the OFF state. When the heated seat switch is pressed, the climate control seat module applies battery positive voltage through the heated seat element supply voltage circuit to the seat cushion and seat back heating elements, initially setting the seat temperature to high heat. Then with each additional activation of the switch, the climate control seat module will cycle the temperature setting to MED, LOW, and OFF. The module will also turn off the heated seat function whenever the ignition switch is turned to the OFF position.

### 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 heat position, 39.5°C (103.1°F) when in the medium heat position, and 37°C (98.6°F) when in the low heat position. The climate control seat module monitors the seat temperature through the temperature sensor signal circuit and the temperature sensor (thermistor) that is located in the seat cushion. The temperature sensor is a variable resistor, its resistance changes as the temperature of the seat changes. When the temperature sensor resistance indicates to the climate control seat module that the seat has reached the desired temperature, the module turns off the element supply voltage to the seat heating elements. The module will then cycle the element supply voltage on and off in order to maintain the desired temperature.

### Vented Seat Modes of Operation

When the ventilation seat system is active, it is designed to draw cabin air around and away from the occupant through small holes in the seat cushion and seat back covers, through channels in the foam pad, and then through the blower motor exhausting the waste air under the seat cushion.

Battery positive voltage is supplied at all times to the driver seat blower motors from the DPM Fuse located in the left rear fuse block. Battery positive voltage is also supplied at all times to the front passenger seat blower motors from the RF HTD ST/S-BAND fuse located in the right rear fuse block. Both, the driver seat and passenger seat blower motors are grounded through their ground circuits and G307. When a vented seat switch is pressed, the climate control seat module sends a low side pulse width modulation (PWM) signal through the blower motor control circuits to the seat cushion and seat back blower motors indicating the vented seat command. In response to this signal, the logic in the blower motors set the blower speed to the switch set point. The blower motors then run drawing cabin air around and away from occupant. The following describes the High, MED, and Low ventilation modes of operation:

• | High Ventilation -- This mode cancels all previous modes and initiates a ventilation cycle with the Under-Cool and Super-Cool Features active. See below for the description of these features. See below for the description of these features.

| In the high mode, both the seat cushion and seat back blowers are ON at a 95 percent duty cycle that provides 100 percent blower performance.

• | Medium Ventilation -- This mode operates identically to the High Ventilation with the exception that the setting is different and the blowers are ON at a 85 percent duty cycle that provides 80 percent blower performance.

• | Low Ventilation -- This mode operates identically to the High Ventilation with the exception that the setting is different and the blowers of medium ventilation are ON at a 75 percent duty cycle that provides 60 percent blower performance.

During vented seat modes of operation, the climate control seat module uses Under-cool and Super Under cool Features in order to keep the seat temperature above pre-determined set point temperatures. See below for the description of these features:

#### Under-Cool Feature

• | The under-cool feature set point is 15°C (59°F).

• | The climate control seat module under-cool feature is active when the system is in any one of the 3 High, MED, or Low ventilation modes. The under-cool feature will initiate a heat cycle when it detects that the seat temperature reached its set point of 15°C (59°F). This means that if the seat temperature reaches this set point, it is possible for both, the blowers and heaters to be on at the same time. Then if the control module does not detect that the operating temperature is above the set point within 90 seconds of the initiation of under-cool mode, the module will shut down and cease operation.

#### Super Under-Cool Feature

• | The super under-cool feature set point is 15°C (59°F).

• | The super under-cool feature is also active when the system is in any of the three ventilation modes. This feature is meant as a secondary precautionary measure. The super under-cool feature will turn off the blower motor and initiate a heat cycle when it detects that the seat temperature reached its set point of 110°C (59°F). This means that it is possible for the seat heaters to be on and the blowers off while in the ventilation mode. Then if the control module does not detect that the operating temperature is above the set point within 90 seconds of the initiation of super under-cool mode, the module will shut down and cease operation.

### Load Management

The 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/vented seat system is one of the vehicle loads that is subject reduction during a battery discharge condition. For more information on load management refer to Load Shed System Description and Operation and Body Control System Description and Operation .