Yukon 4WD V8-5.3L (2008)
3. Verify that the rear heated seat modes are being displayed correctly by the rear HVAC/RSA module.
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If the rear heated seat mode are not displayed correctly, replace the rear HVAC/RSA module.
4. If all the tests are normal replace the rear heated seat module.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. See: Powertrain Management/Computers and Control
Systems/Testing and Inspection/Diagnostic Trouble Code Tests and Associated Procedures/Verification Tests and Procedures
Heated/Cooled Seats Inoperative
Heated/Cooled Seats Inoperative
Diagnostic Instructions
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Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection/Initial Inspection and
Diagnostic Overview/Diagnostic System Check - Vehicle
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Review Strategy Based Diagnosis for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Circuit/System Description
The heated cooled seat system operation is controlled through the switch inputs of the HVAC control module. When a heated or cooled 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 cooled seat switch
inputs and determines the appropriate operating mode. When a heated or cooled seat function is activated the MSM will send a GMLAN message to the
HVAC control module to illuminate the appropriate indicators and a PWM message to the climate control seat module (CCSM) to activate the
appropriate heated cooled seat function. The CCSM controls heat/cool seat ventilation blowers located under the seat cushion and behind the seat back.
The ventilation blowers are self contained electronic air conditioners consisting of a blower motor with an inlet air filter, thermal electric device (TED),
temperature sensor, and waste air duct. The air flow from the blower is divided into 2 streams and directed across both sides of the TED, one side into
vent passages through the seat foam and the other out the waste air duct. While the system is operating in either the heat or cool modes both heated and
cooled air is generated as it passes across the TED. When voltage is applied to a TED, one side releases energy as heat, while the opposite side absorbs
energy and gets cold. The supply voltage to the TEDs is controlled by the CCSM and the polarity determines which side gets hot or cool. When the
polarity of the current flow to the TEDs is switched, the hot and cool sides of the TED reverse. The CCSM monitors the temperature of the air flow into
the seat foam and continuously adjusts the blower speed and TED temperature by regulating the current flow through each component. The CCSMs rely
on inputs from temperature sensors located in the ventilation blowers near the TEDs to control seat temperatures. The thermistors are 2 wire sensors
supplied with a 5-volt referenced signal circuit and a low reference circuit from the CCSM. Resistance through the thermistors varies with temperature
causing the heated seat sensor signal circuit voltage levels to decrease as the TED temperatures rise.
Diagnostic Aids
The following conditions must be met in order to perform valid tests when diagnosing the climate control seat (CCS) system:
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The ignition must be cycled OFF then ON between each test in order to reset the CCSM.
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The engine must be running in order to supply the CCSM with the amount of current needed to operate the heated/cool seat system.
Circuit/System Verification
1. Engine running, verify that the heated cooled seat indicators function normally as the driver and passenger seat heat and cool functions are
attempted to be operated.
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If the heated cooled seat indicators do not function normally perform the Heated Cooled Seat Indicator Circuit Test.
2. Verify that the driver and passenger seat heat and cool modes function normally.
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If all of the driver and passenger seat heat and cool functions are inoperative, perform the Driver and Passenger Heated/Cool Seats Circuit
Test.
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If any of the heated cooled seat functions are inoperative for one of the front seats perform the Driver or Passenger Heated/Cool Seat Circuit
Test
Circuit/System Testing
Heated Cooled Seat Indicator Circuit Test
