Heated Seat Inoperative (Chevy and GMC)

Heated Seat Inoperative (Chevy and GMC)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The heated seat system operation is controlled through the switch inputs to the driver and passenger door modules. When a heated seat switch is pressed a GMLAN message is sent to the memory seat module (MSM) indicating the switch is active. The MSM monitors the heated seat switch inputs and determines the appropriate operating mode. When a heated seat function is activated the MSM will send a GMLAN message to the door module to illuminate the appropriate indicators. The memory seat module controls the voltage supply and the ground circuits to the seat heater elements. When a heated seat function is commanded active, the seat module will switch battery voltage to the heater element supply circuits, and ground is provided through pulse width modulation (PWM) low side drive control circuits. During heated seat operation both the seat back and cushion heater elements are supplied battery voltage. The seat module grounds the appropriate control circuits for back only or back and cushion heating modes, and opens or closes the active control circuits as necessary in order to maintain the desired seat temperature. The seat module relies on 4 independent inputs from thermistors located in the seat back and seat cushion of the driver and passenger seats to control heated seat temperatures. The thermistors are 2-wire sensors supplied with a 5-volt referenced signal circuit and a low reference circuit from the seat module. Resistance through the thermistors varies with temperature causing the heated seat sensor signal circuit voltage levels to decrease as the seat temperatures rise.

Circuit/System Testing

1. Ignition ON, verify that the driver and passenger door switch heated seat switch parameters display Active while the heated seat switches are pressed.

^ If either of the switch parameters are continuously Active or Inactive while the switch is pressed, perform the heated seat switch circuit test.

2. Verify that the MSM driver and passenger seat HVC mode and level parameters are displayed correctly as the heated seat switches are activated through all of the operating modes.

^ If the MSM parameters are not displayed correctly replace the MSM.

3. If the circuits test normal replace the driver or passenger door module.

Component Testing

1. Disconnect the heated seat switch connector at the door module.
2. Connect a fused jumper wire from the low reference circuit terminal 4 to ground.
3. Verify that a test lamp does not illuminate when connected from battery voltage to the switch signal circuit terminals 6 and 7.

^ If the test lamp illuminates while the switches are in an inactive state, replace the heated seat switch.

4. Verify that a test lamp illuminates when connected from battery voltage to the switch signal circuit terminals 6 and 7 while pressing the heated seat switches.

^ If the test lamp does not illuminate while the switches are in an active state, replace the heated seat switch.

5. Verify that the heated seat switch indicators illuminate with a test lamp connected from battery voltage to the indicator control circuit terminals 1, 2, 9, 10, and 11.

^ If the indicators do not illuminate replace the heated seat switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Front Seat Heater Switch Replacement (w/o KB6)