The heat and cool seat functions for the driver and passenger seats are controlled by the climate control seat module (CCSM) that is located under the passenger seat cushion. When a driver or passenger heat or cool seat switch is pressed, a low reference signal is applied through the switch signal circuit to the door control module. In response to the switch input, the door module sends a serial data message to the memory seat module (MSM) indicating the heat/cool seat request. The MSM then sends a pulse width modulation (PWM) signal through the heated/cooled seat mode signal circuit to the CCSM. The CCSM then applies battery positive 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.

Ignition ON and the passenger heat or cool seat is commanded On.

The temperature difference between the seat cushion and the seat back temperature sensors is greater than 40°C (104°F) for more than 4 seconds.

The CCSM will disable the heat or cool seat function for the current ignition cycle.

The current DTC clears when the malfunction is no longer present and the power mode changes to OFF then back to ACC or RUN.

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

Important: If other DTCs set along with B272D, diagnosis those DTCs first before performing this circuit/system test. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

Ignition ON, press the passenger heated seat cushion/back heat mode switch. The heated seat switch temperature indicators should illuminate and the seat should operate in the high heat mode. Press the heated seat back only mode switch, the heated seat switch temperature indicators should illuminate and the seat should operate in the back only heat mode. Press the heated seat cool mode switch, the heated seat switch temperature indicators should illuminate and the seat should operate in the cool mode.

1. Disconnect the harness connector at the passenger seat cushion ventilation heat and cool module.
2. Connect a test lamp between the heat control circuit terminal 1 and ground.
3. Ignition ON, command the Passenger Seat Heat Cmd. ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit test normal, replace the CCSM.

4. Connect a test lamp between the cool control circuit terminal 3 and ground.
5. Ignition ON, command the Passenger Seat Cool Cmd. ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit test normal, replace the CCSM.

6. Connect the harness connector at the seat cushion ventilation heat and cool module and disconnect the harness connector at the seat back ventilation heat and cool module.
7. Connect a test lamp between the heat control circuit terminal 1 and ground.
8. Ignition ON, command the Passenger Seat Heat Cmd. ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between commanded states.

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

⇒	If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit test normal, replace the CCSM.

9. Connect a test lamp between the cool control circuit terminal 3 and ground.
10. Ignition ON, command the Passenger Seat Cool Cmd. ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between commanded states.

⇒	If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit test normal, replace the CCSM.

11. Disconnect the harness connector at the seat cushion 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 following conditions 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.
12. On the seat cushion ventilation module side of the harness connector, 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, test or replace the seat cushion ventilation heat and cool module.

13. On the seat back ventilation module side of the harness connector, 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, test or replace the seat back ventilation heat and cool module.

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

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 ohms-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 following conditions 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.