Heated Seat Inoperative Chevy and GMC

The driver and front passenger heated seats are controlled by separate heated seat switches located on the door panels. When a heated seat switch is pressed, ground is momentarily applied through the switch contacts and the switch signal circuit to the door control module. In response to this signal, the door module sends a serial message to the memory seat module (MSM) or heated seat module (HSM) indicating the heat seat request. The module then applied battery voltage to the seat cushion and seat back heater elements through a common voltage supply circuit. Each individual heater element is grounded by the module through separate low side drive control circuits. The heater element control circuits are pulse width modulated (PWM) to ground by the module in order to control the seat temperatures by regulating the current flow through the heater elements. The MSM/HSM relies on 4 independent inputs from temperature sensors (thermistors) located in the seat back and seat cushion of the driver and passenger seats. The temperature sensor resistance varies based on the temperature of the heating element causing the signal circuit voltage to change. Once the seat reaches the switch set temperature, the MSM/HSM will then cycle the control circuits of the heating elements ON and OFF in order to maintain the desired seat temperature based on the feedback voltage from the sensors. The MSM/HSM then monitors the current flow through the heating elements and the of rate change of the temperature sensor to verify correct heated seat operation.

Schematic Reference

Heated/Cooled Seat Schematics

Connector End View Reference

Heated/Cooled Seat Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, observe the appropriate scan tool Driver Door Switch or Passenger Door Switch parameters listed below while pressing and releasing the appropriate switch. The readings should change between Inactive and Active.

•	Seat Back Heat Mode Sw.

•	Seat Heat Mode Sw.

⇒	If not the specified values, refer to the Heated Seat Switch component test. If the heated seat switch tests normal, replace the appropriate door module

2. If all scan tool parameters test normal and there are no DTCs set, replace the MSM/HSM.
3. If all heated seat functions operate normal and the heated seat switch indicators do not illuminate, refer to the Heated Seat Switch Indicators component test.

Heated Seat Switch

1. Ignition OFF, disconnect the C4 harness connector at the door module.
2. Test for infinite resistance between the signal circuits listed below and the low reference circuit terminal 4 with the switch in the open position.

•	Seat back and cushion heat mode terminal 6

•	Seat back only mode terminal 7

⇒	If not the specified value, replace the heated seat switch.

3. Test for less than 2 ohms between the signal circuits listed below and the low reference circuit terminal 4 with the switch in the closed position.

•	Seat back and cushion heat mode terminal 6

•	Seat back only mode terminal 7

⇒	If greater than the specified range for any of the tests, replace the heated seat switch.

Heated Seat Switch Indicators

1. Ignition OFF, disconnect the C4 harness connector at the door module.
2. Connect a 3A fused jumper wire between the low reference circuit terminal 4 and ground.
3. Connect a test lamp between B+ and each control circuit listed below. The appropriate indicator should illuminate.

•	Seat back and cushion mode indicator terminal 10

•	Seat back only mode indicator terminal 11

•	Low heat indicator terminal 9

•	Medium heat indicator terminal 1

•	High heat indicator terminal 2

⇒	If any indicator does not illuminate, replace the heated seat switch.

4. If all indicators illuminate, replace the door module.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Heated Seat Inoperative Cadillac

The driver and front passenger heated seats are controlled through the switch inputs of the HVAC control module. When a heated seat switch is pressed a serial data message is sent from the HVAC control module to the memory seat module (MSM) indicating the heated seat request. In response to this message, the MSM applies battery voltage to the heater element supply voltage circuit and ground through pulse width modulation (PWM) low side drive control circuits activating the heated seat. Once the heated seat is activated, the MSM then sends a serial data message back to the HVAC control module to illuminate the appropriate switch indicators. The MSM relies on 4 independent inputs from thermistors located in the seat back and seat cushion of the driver and passenger seats to control seat temperatures. The thermistors are 2-wire temperature sensors supplied with a 5-volt referenced signal circuit and a low reference circuit from the MSM. Resistance through the sensors varies with seat temperature causing the signal circuit voltage levels to decrease as the seat temperatures rise.

Schematic Reference

Heated/Cooled Seat Schematics

Connector End View Reference

Heated/Cooled Seat Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, observe the HVAC control panel while pressing and releasing the appropriate heated seat switch. The appropriate switch symbol should be displayed on the control panel.

⇒	If the symbol is not displayed, replace the HVAC control module.

2. If the heated seat switch symbols test normal and there are no DTCs set, replace the MSM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Refer to Control Module References for MSM or HVAC control module replacement, programming, and setup