• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
B+ | 1 | 1 | -- | -- |
Ignition Voltage | 1 | 1 | -- | -- |
Driver/Passenger Seat Blower Supply Voltage | 2 | 2 | -- | -- |
Left Heated/Cooled Seat Mode Signal | 2 | 2 | 2 | -- |
Right Heated/Cooled Seat Mode Signal | 2 | 2 | 2 | -- |
Seat Back Temperature Sensor Signal | 2 | 2 | 2 | -- |
Seat Cushion Temperature Sensor Signal | 2 | 2 | 2 | -- |
Seat Back Heated/Cool Ventilation Module Cool Control | 1 | 2 | -- | -- |
Seat Back Heated/Cool Ventilation Module Heat Control | 1 | 2 | -- | -- |
Seat Cushion Heated/Cool Ventilation Module Cool Control | 1 | 2 | -- | -- |
Seat Cushion Heated/Cool Ventilation Module Heat Control | 1 | 2 | -- | -- |
Seat Back Blower Speed Control | 2 | 2 | 3 | -- |
Seat Cushion Blower Speed Control | 2 | 2 | 3 | -- |
Heated Seat Switch Low Reference | -- | 2 | -- | -- |
Seat Blower Low Reference | -- | 2 | -- | -- |
Seat Back Temperature Sensor Low Reference | -- | 2 | -- | -- |
Seat Cushion Temperature Sensor Low Reference | -- | 2 | -- | -- |
Module Ground | -- | 1 | -- | -- |
1. Driver and passenger heated/cooled seats are inoperative 2. Seat heat and cool modes are inoperative 3. Heated/cooled seats temperature adjustment is inoperative |
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:
• | The ignition must be cycled OFF then ON between each test in order to reset the CCSM. |
• | The engine must be running in order to supply the CCSM with the amount of current needed to operate the heated/cool seat system. |
Heated/Cooled Seats Description and Operation
Control Module References for scan tool information
⇒ | If the symbol is not displayed, replace the HVAC control module. |
• | 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. |
⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance. |
⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. |
⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. |
⇒ | 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.
• | 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.
• | 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. |
⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the CCSM. |
⇒ | 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.
• | 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.
• | 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. |
⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the CCSM. |
⇒ | 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.
• | 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.
• | 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. |
⇒ | 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.
• | 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
• | 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. |
⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the CCSM. |
⇒ | 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.
• | 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.
• | 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. |
⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the CCSM. |
⇒ | 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.
• | 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.
• | 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. |
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.
⇒ | 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
⇒ | 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.
⇒ | 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.
⇒ | If not within the specified range, replace the ventilation heat and cool module. |
°C | °F | OHMS |
---|---|---|
Temperature vs Resistance Values (Approximate) | ||
60° | 140° | 319.9 |
50° | 122° | 433.1 |
40° | 104° | 596.6 |
30° | 86° | 837.5 |
20° | 68° | 1200 |
10° | 50° | 1757 |
0° | 32° | 2633 |
-10° | 14° | 4047 |
-20° | -4° | 6401 |
-30° | -22° | 10,450 |
-40° | -40° | 17,670 |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for the MSM and CCSM replacement, setup, and programming |