Heated/Cooled Seats Inoperative Z75

The heat and cool seat functions for both the driver and passenger seats is controlled by the climate control seat module that is located under the passenger seat cushion. The heated and cooled seat switches are located in the HVAC control module. When a heated or cooled seat switch is pressed a serial data message from the HVAC control module is sent to the memory seat module (MSM) indicating the heat/cool seat request. The MSM then sends a pulse width modulation (PWM) signal through the appropriate heated/cooled seat mode signal circuit to the climate control seat module (CCSM) to activate the heated or cooled seat function. The CCSM then applies battery voltage to the seat cushion and seat back thermal electronic devices (TEDs) and a pre-determined voltage to the blower motors. To determine seat temperature, the CCSM supplies a 5 volt signal and a low reference to the temperature sensors that are attached to each TED. The temperature sensors are variable resistors, their resistance changes as the temperature of the seat changes. Then based on the seat temperature, the CCSM controls the voltage level that it applies to the TEDs and blower motors.

The following conditions must be met in order to perform valid tests when diagnosing the climate control seat (CCS) system:

Schematic Reference

Heated/Cooled Seat Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Heated/Cooled Seats Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the HVAC control panel while pressing and releasing the appropriate heated or cooled 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. Operate the driver and passenger heated and cooled seats through the modes of operation listed below. The seat should operate in all three modes.

•	Seat back and cushion heat mode

•	Back only heat mode

•

Cool mode

⇒	If both, the driver and passenger heated/cool seats are inoperative, refer to Driver and Passenger Heated/Cool Seats Inoperative.

⇒	If the driver heated/cool seat is inoperative, refer to Driver Heated/Cool Seat Inoperative.

⇒	If the passenger heated/cool seat is inoperative, refer to Passenger Heated/Cool Seat Inoperative.

Driver and Passenger Heated/Cool Seats Inoperative

1. Ignition OFF, disconnect the X1 harness connector at the CCSM.
2. Verify that a test lamp illuminates between the ground circuit terminal M and B+.

⇒	If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Verify that a test lamp illuminates between the B+ circuit terminal E and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

4. Disconnect the X2 harness connector at the CCSM.
5. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 1 and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

6. If all circuits test normal, replace the CCSM.

Driver Heated/Cool Seat Inoperative

1. Ignition OFF, disconnect the X1, X2, X3 harness connectors at the CCSM.
2. Connect a test lamp between the signal circuit terminal 14 X3 and B+.
3. Ignition ON, press the HEAT or COOL seat switch through the high, medium, and low positions to OFF. The test lamp should illuminate until the OFF position is reached.

⇒	If the test lamp does not illuminate, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the MSM.

⇒	If the test lamp is ON with the switch in the OFF position, test the signal circuit for a short to ground. If the circuit tests normal, replace the MSM.

Important:  If the resistance is measured with the seat still warm or cool, the resistance values will vary. At 68°F, (20°C) the nominal resistance value is 1200 ohms ±5 percent. For warmer or cooler ambient temperatures, refer to the Temperature vs Resistance table below. The delta resistance values between the seat cushion and seat back temperature sensors should not be greater than 2000 ohms.

4. Ignition OFF, test for 300-18K ohms between the signal and low reference circuits listed below:

•	Seat cushion temperature sensor signal circuit terminal 7 X2 and low reference circuit terminal 8 X2.

•	Seat back temperature sensor signal circuit terminal 9 X2 and low reference circuit terminal 10 X2.

⇒	If greater than the specified range, test the signal and low reference circuits for a short to voltage or an open/high resistance. If the circuits test normal, test or replace the appropriate seat cushion or seat back heat/cool seat ventilation blower.

⇒	If less than the specified range, test for a short between the signal and low reference circuits. If the circuits test normal, test or replace the appropriate seat cushion or seat back heat/cool seat ventilation blower.

Important: The test leads must be connected in the correct polarity, otherwise lower out of range values will appear. Use the Positive Lead for the COOL control circuit and the Negative Lead for the HEAT control circuit. If the resistance is measured with the seat still warm or cool, the resistance values will vary even if the system was powered up for just a few seconds. The TED must be allowed to stabilize to room temperature prior to a measurement. The conditions listed below will change the resistance to out of range values:

•	The test leads are incorrectly connected.

•	Air blowing across the TED.

•	Measuring the resistance at other than room temperature of 70°F (21°C).

•	Holding the TED portion of the heat/cool seat ventilation blower in your hand.

In warmer or cooler climates where room temperature conditions of 70°F (21°C) may be unattainable, resistance values may read above the specified range. Use a heat gun or a blower to warm or cool the TED while measuring the resistance. The resistance values should slowly lower toward the specified range.
5. Test for 0.9-10.0 ohms between the control circuits listed below:

•	Seat cushion heat control circuit terminal G X1 and cool control circuit terminal H X1

•	Seat back heat control circuit terminal J X1 and cool control circuit terminal K X1

⇒	If greater than the specified range, test the appropriate control circuits for an open/high resistance. If the circuits test normal, test or replace the appropriate seat cushion or seat back heat/cool seat ventilation blower.

⇒	If less than the specified range, test for a short between the appropriate control circuits. If the circuits test normal, test or replace the appropriate seat cushion or seat back heat/cool seat ventilation blower.

6. Connect the X1, X2, X3 harness connectors to the CCSM.
7. Disconnect the harness connector at the seat cushion heat/cool seat ventilation blower.
8. Test for less than 5 ohms between the low reference circuit terminal 4 and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the CCSM.

9. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal 5 and ground.

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

⇒	If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the CCSM.

Important: The ignition must be cycled OFF then ON between each test in order to reset the CCSM.

10. Ignition OFF then ON, connect a test lamp between the control circuits listed below and ground. Press the HEAT switch when testing the heat control circuit and the COOL switch when testing the cool control circuit. The test lamp should illuminate or slowly illuminate for approximately 2-4 seconds after the switch is pressed. On the heat control circuit, the test lamp may exhibit a 4 second delay before it starts to illuminate.

•	Seat cushion heat control circuit terminal 1

•	Seat cushion cool control circuit terminal 3

⇒	If the test lamp does not illuminate, test the appropriate control circuit for a short to ground. If the circuit tests normal, replace the CCSM.

⇒	If the test lamp is always ON, test the appropriate control circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

Important: The ignition must be cycled OFF then ON between each test in order to reset the CCSM.

11. Ignition OFF then ON, connect a test lamp between the circuits listed below and ground. The test lamp should illuminate or slowly illuminate for approximately 5 seconds after pressing the HEAT switch.

•	Seat cushion blower motor control terminal 2

•	Seat cushion blower motor speed control terminal 7

⇒	If the test lamp does not illuminate, test the appropriate circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the CCSM.

⇒	If the test lamp is always ON, test the appropriate circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

12. Ignition OFF, connect the harness connector to the seat cushion heat/cool seat ventilation blower.
13. Disconnect the harness connector at the seat back heat/cool seat ventilation blower.
14. Test for less than 5 ohms between the low reference circuit terminal 4 and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the CCSM.

15. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal 5 and ground.

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

⇒	If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the CCSM.

Important: The ignition must be cycled OFF then ON between each test in order to reset the CCSM.

16. Ignition OFF then ON, connect a test lamp between the control circuits listed below and ground. Press the HEAT switch when testing the heat control circuit and the COOL switch when testing the cool control circuit. The test lamp should illuminate or slowly illuminate for approximately 4 seconds after the switch is pressed. On the heat control circuit, the test lamp may exhibit a 4 second delay before it starts to illuminate.

•	Seat back heat control circuit terminal 1

•	Seat back cool control circuit terminal 3

⇒	If the test lamp does not illuminate, test the appropriate control circuit for a short to ground. If the circuit tests normal, replace the CCSM.

⇒	If the test lamp is always ON, test the appropriate control circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

Important: The ignition must be cycled OFF then ON between each test in order to reset the CCSM.

17. Ignition OFF then ON, connect a test lamp between the circuits listed below and ground. The test lamp should illuminate or slowly illuminate for approximately 5 seconds after pressing the HEAT switch.

•	Seat back blower motor control circuit terminal 2

•	Seat cushion blower motor speed control terminal 7

⇒	If the test lamp does not illuminate, test the appropriate circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the CCSM.

⇒	If the test lamp is always ON, test the appropriate circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

18. If all circuits test normal, test or replace the appropriate seat cushion or seat back heat/cool seat ventilation blower.

Passenger Heated/Cool Seat Inoperative

1. Ignition OFF, disconnect the X1, X2, X3 harness connectors at the CCSM.
2. Connect a test lamp between the signal circuit terminal 6 X3 and B+.
3. Ignition ON, press the HEAT or COOL seat switch through the high, medium, and low positions to OFF. The test lamp should illuminate until the OFF position is reached.

⇒	If the test lamp does not illuminate, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the MSM.

⇒	If the test lamp is ON with the switch in the OFF position, test the signal circuit for a short to ground. If the circuit tests normal, replace the MSM.

Important:  If the resistance is measured with the seat still warm or cool, the resistance values will vary. At 68°F (20°C), the nominal resistance value is 1200 ohms ±5 percent. For warmer or cooler ambient temperatures, refer to the Temperature vs Resistance table below. The delta resistance values between the seat cushion and seat back temperature sensors should not be greater than 2000 ohms.

4. Ignition OFF, test for 300 ohms-18K ohms between the signal and low reference circuits listed below:

•	Seat cushion temperature sensor signal circuit terminal 2 X2 and low reference circuit terminal 3 X2.

•	Seat back temperature sensor signal circuit terminal 4 X2 and low reference circuit terminal 5 X2.

⇒	If greater than the specified range, test the signal and low reference circuits for a short to voltage or an open/high resistance. If the circuits test normal, test or replace the appropriate seat cushion or seat back heat/cool seat ventilation blower.

⇒	If less than the specified range, test for a short between the signal and low reference circuits. If the circuits test normal, test or replace the appropriate seat cushion or seat back heat/cool seat ventilation blower.

Important: The test leads must be connected in the correct polarity, otherwise lower out of range values will appear. Use the Positive Lead for the COOL control circuit and the Negative Lead for the HEAT control circuit. If the resistance is measured with the seat still warm or cool, the resistance values will vary even if the system was powered up for just a few seconds. The TED must be allowed to stabilize to room temperature prior to a measurement. The conditions listed below will change the resistance to out of range values:

•	The test leads are incorrectly connected.

•	Air blowing across the TED

•	Measuring the resistance at other than room temperature of 70°F (21°C)

•	Holding the TED portion of the heat/cool seat ventilation blower in your hand

In warmer or cooler climates where room temperature conditions of 70°F (21°C) may be unattainable, resistance values may read above the specified range. Use a heat gun or a blower to warm or cool the TED while measuring the resistance. The resistance values should slowly lower toward the specified range.
5. Test for 0.9-10.0 ohms between the control circuits listed below:

•	Seat cushion heat control circuit terminal A X1 and cool control circuit terminal B X1

•	Seat back heat control circuit terminal C X1 and cool control circuit terminal D X1

⇒	If greater than the specified range, test the appropriate control circuits for an open/high resistance. If the circuits test normal, test or replace the appropriate seat cushion or seat back heat/cool seat ventilation blower.

⇒	If less than the specified range, test for a short between the appropriate control circuits. If the circuits test normal, test or replace the appropriate seat cushion or seat back heat/cool seat ventilation blower.

6. Connect the X1, X2, X3 harness connectors to the CCSM.
7. Disconnect the harness connector at the seat cushion heat/cool seat ventilation blower.
8. Test for less than 5 ohms between the low reference circuit terminal 4 and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the CCSM.

9. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal 5 and ground.

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

⇒	If less than the specified range, replace the CCSM.

Important: The ignition must be cycled OFF then ON between each test in order to reset the CCSM.

10. Ignition OFF then ON, connect a test lamp between the control circuits listed below and ground. Press the HEAT switch when testing the heat control circuit and the COOL switch when testing the cool control circuit. The test lamp should illuminate or slowly illuminate for approximately 2-4 seconds after the switch is pressed. On the heat control circuit, the test lamp may exhibit a 4 second delay before it starts to illuminate.

•	Seat cushion heat control circuit terminal 1

•	Seat cushion cool control circuit terminal 3

⇒	If the test lamp does not illuminate, test the appropriate control circuit for a short to ground. If the circuit tests normal, replace the CCSM.

⇒	If the test lamp is always ON, test the appropriate control circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

Important: The ignition must be cycled OFF then ON between each test in order to reset the CCSM.

11. Ignition OFF then ON, connect a test lamp between the circuits listed below and ground. The test lamp should illuminate or slowly illuminate for approximately 5 seconds after pressing the HEAT switch.

•	Seat cushion blower motor control terminal 2

•	Seat cushion blower motor speed control terminal 7

⇒	If the test lamp does not illuminate, test the appropriate circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the CCSM.

⇒	If the test lamp is always ON, test the appropriate circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

12. Ignition OFF, connect the harness connector to the seat cushion heat/cool seat ventilation blower.
13. Disconnect the harness connector at the seat back heat/cool seat ventilation blower.
14. Test for less than 5 ohms between the low reference circuit terminal 4 and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the CCSM.

15. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal 5 and ground.

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

⇒	If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the CCSM.

Important: The ignition must be cycled OFF then ON between each test in order to reset the CCSM.

16. Ignition OFF then ON, connect a test lamp between the control circuits listed below and ground. Press the HEAT switch when testing the heat control circuit and the COOL switch when testing the cool control circuit. The test lamp should illuminate or slowly illuminate for approximately 4 seconds after the switch is pressed. On the heat control circuit, the test lamp may exhibit a 4 second delay before it starts to illuminate.

•	Seat back heat control circuit terminal 1

•	Seat back cool control circuit terminal 3

⇒	If the test lamp does not illuminate, test the appropriate control circuit for a short to ground. If the circuit tests normal, replace the CCSM.

⇒	If the test lamp is always ON, test the appropriate control circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

Important: The ignition must be cycled OFF then ON between each test in order to reset the CCSM.

17. Ignition OFF then ON, connect a test lamp between the circuits listed below and ground. The test lamp should illuminate or slowly illuminate for approximately 5 seconds after pressing the HEAT switch.

•	Seat back blower motor control circuit terminal 2

•	Seat back blower motor speed control terminal 7

⇒	If the test lamp does not illuminate, test the appropriate circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the CCSM.

⇒	If the test lamp is always ON, test the appropriate circuit for a short to voltage. If the circuit tests normal, replace the CCSM.

18. If all circuits test normal, test or replace the appropriate seat cushion or seat back heat/cool seat ventilation blower.

Ventilation Heat and Cool Module

1. Ignition OFF, disconnect the harness connectors at the seat cushion and seat back ventilation heat and cool modules.

Important: If the resistance is measured with the seat still warm or cool, the resistance values will vary. At 68°F (20°C), the nominal resistance value is 1200 ohms ±5 percent. For warmer or cooler ambient temperatures, refer to the Temperature vs Resistance table below. The delta resistance values between the seat cushion and seat back temperature sensors should not be greater than 2000 ohms.

2. Test for 300-18K ohms between the temperature sensor signal circuit terminal 5 and the low reference circuit terminal 8.

⇒	If not within the specified range, replace the ventilation heat and cool module.

Important: The test leads must be connected in the correct polarity, otherwise lower out of range values will appear. Use the Positive Lead for the COOL control circuit and the Negative Lead for the HEAT control circuit. If the resistance is measured with the seat still warm or cool, the resistance values will vary even if the system was powered up for just a few seconds. The TED must be allowed to stabilize to room temperature prior to a measurement. The conditions listed below will change the resistance to out of range values:

•	The test leads are incorrectly connected.

•	Air blowing across the TED

•	Measuring the resistance at other than room temperature of 70°F

•	Holding the TED portion of the heated and cool ventilation module in your hand

In warmer or cooler climates where room temperature conditions of 70°F (21°C) may be unattainable, resistance values may read above the specified range. Use a heat gun or a blower to warm or cool the TED while measuring the resistance. The resistance values should slowly lower toward the specified range.
3. Test for 0.9-10.0 ohms between the heat control circuit terminal 1 and the cool control circuit terminal 3.

⇒	If not within the specified range, replace the ventilation heat and cool module.

Important: The test leads must be connected in the correct polarity, otherwise higher out of range values will appear. Use the Positive Lead for the control circuit and the Negative Lead for the ground circuit.

4. Test for 6-9k ohms between blower motor control circuit terminal 2 and the low reference circuit terminal 4.

⇒	If not within the specified range, replace the ventilation heat and cool module.

Important: The test leads need to be connected in the correct polarity, otherwise higher out of range values will appear. Use the Positive Lead for the speed control circuit and the Negative Lead for the ground circuit.

5. Test for 290-420K ohms between blower motor speed control circuit terminal 7 and the low reference circuit terminal 4.

⇒	If not within the specified range, replace the ventilation heat and cool module.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.