For 1990-2009 cars

### Diagnostic Instructions

• | 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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Driver Seat Back Ventilation Heating and Cooling Module B+ | 1, 4 | 2 | -- | --
Driver Seat Cushion Ventilation Heating and Cooling Module B+ | 1, 4 | 3 | -- | --
Driver Cooled Seat Signal | 1 | 1 | 1 | --
Driver Cooled Seat Switch Signal | 1 | 1 | 1 | --
Driver Cooled Seat Indicator Control | 7 | 7 | 8 | --
Driver Cooled Seat High Indicator Control | 7 | 7 | 8 | --
Driver Cooled Seat Medium Indicator Control | 7 | 7 | 8 | --
Driver Cooled Seat Low Indicator Control | 7 | 7 | 8 | --
Driver Seat Back Ventilation Heating and Cooling Module Ground | -- | 2 | -- | --
Driver Seat Cushion Ventilation Heating and Cooling Module Ground | -- | 3 | -- | --
Passenger Seat Back Ventilation Heating and Cooling Module B+ | 1, 4 | 5 | -- | --
Passenger Seat Cushion Ventilation Heating and Cooling Module B+ | 1, 4 | 6 | -- | --
Passenger Cooled Seat Signal | 4 | 4 | 4 | --
Passenger Cooled Seat Switch Signal | 4 | 4 | 4 | --
Passenger Cooled Seat Indicator Control | 7 | 7 | 8 | --
Passenger Cooled Seat High Indicator Control | 7 | 7 | 8 | --
Passenger Cooled Seat Medium Indicator Control | 7 | 7 | 8 | --
Passenger Cooled Seat Low Indicator Control | 7 | 7 | 8 | --
Passenger Seat Back Ventilation Heating and Cooling Module Ground | -- | 5 | -- | --
Passenger Seat Cushion Ventilation Heating and Cooling Module Ground | -- | 6 | -- | --
1. Driver cooled seat is inoperative 2. Driver cooled seat back is inoperative 3. Driver cooled seat cushion is inoperative 4. Passenger cooled seat is inoperative 5. Passenger cooled seat back is inoperative

6. Passenger cooled seat cushion is inoperative

7. Heated and cooled seat switch indicator inoperative

8. Heated and cooled seat switch indicator always On

### Circuit/System Description

The driver and passenger cooled seats are controlled by separate cooled seat switches located in the center console. Battery voltage is supplied at all times to the driver and passenger seat ventilation modules from the HTD/SEAT fuse located in the I/P fuse block. Ground for the driver seat ventilation modules is provided at G303, while ground for the passenger seat ventilation modules is provided at G302.

When a cooled seat switch is pressed, the signal circuit from the door switch is pulled low indicating the cooled seat command. In response to this signal, the door switch sends a serial data message to the memory seat module (MSM) indicating the cooled seat command. The MSM sends a low side pulse width modulation (PWM) signal to the seat cushion and seat back ventilation modules indicating the cooled seat command. The MSM then sends a serial data message back to the door switch for it to illuminate the appropriate switch indicators. The ventilation modules then set the blower speeds relative to the switch set point. Both blower motors run blowing cabin air across the thermal electronic devices (TEDs) in order to cool the seat. To determine seat temperature, the ventilation module supplies a 5 V reference voltage and a low reference to the seat cushion and seat back temperature sensors. The sensors are variable resistors, their resistance changes as the temperature of the seat changes. Based on the feedback voltage from the temperature sensors, the ventilation modules control the speed of the blower motors to maintain the seat set temperature.

### Reference Information

#### Schematic Reference

Heated/Cooled Seat Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Cooled Seat Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, observe the scan tool Driver Door Switch Seat Cooled Mode Switch parameter while pressing the driver cooled seat switch. The reading should change between Off and On.

⇒ | If not the specified value, refer to Heated and Cooled Seat Switch Circuit Test.

2. Observe the scan tool Passenger Door Switch Cooled Seat Mode Switch parameter while pressing the passenger cooled seat switch. The reading should change between Off and On.

⇒ | If not the specified value, refer to Heated and Cooled Seat Switch Circuit Test.

3. If all scan tool readings test normal, but the driver and/or passenger cooled seat is inoperative, refer to Cooled Seat Malfunction.
4. If the cooled seat operates normal, but the cooled seat switch indicators are inoperative or always ON, refer to Heated and Cooled Seat Switch Indicators Malfunction.

### Circuit/System Testing

#### Heated and Cooled Seat Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the appropriate heated and cooled seat switch.
2. Test for less than 1 Ω between the ground circuit terminal 7 and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the appropriate scan tool Driver or Passenger Door Switch Seat Cooled Mode Switch parameter is Off.
4. If not the specified value, test the signal circuit terminal 5 for a short to ground. If the circuit tests normal, replace the door module.
5. Install a 3 A fused jumper wire between the signal circuit terminal 5 and ground. Verify the scan tool Seat Cool Mode Switch parameter is On.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the door module.

6. If all circuits test normal, test or replace the heated and cooled seat switch.

#### Cooled Seat Malfunction

1. Ignition OFF, disconnect the harness connector at the appropriate seat ventilation heating and cooling module.
2. Test for less than 1 Ω between the ground circuit terminal C and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal A and ground.

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

4. Connect a test lamp between the signal circuit terminal B and battery voltage.
5. Press the cooled 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 is always OFF, 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 always 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.

6. Test for 2 k - 20 kΩ between the signal circuit terminal D and the low reference circuit terminal E.

⇒ | 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 heater element.

⇒ | If greater than the specified range, test the signal circuit and the low reference circuit 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 heater element.

7. Ignition OFF, connect the harness connector at the seat ventilation heating and cooling module and disconnect the harness connector at the appropriate seat cushion or seat back heater element.
8. Ignition ON, cooled seat ON, test for 4.8 - 5.2 V between the signal circuit terminal D and ground.

⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the seat ventilation heating and cooling module.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the seat ventilation heating and cooling module.

9. If all circuits test normal, test or replace the seat ventilation heating and cooling module.

#### Heated and Cooled Seat Switch Indicators Malfunction

1. Ignition OFF, disconnect the harness connector at the appropriate heated and cooled seat switch.
2. Connect a test lamp between the appropriate control circuit terminal listed below and ground:

• | Seat cool mode indicator terminal 9

• | Low indicator terminal 6

• | Medium indicator terminal 8

• | High indicator terminal 10

3. Ignition ON, command the Door Switch Heated Seat Indicators 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 ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the door module.

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the door module.

4. If all circuits test normal, test or replace the heated and cooled seat switch.

### Component Testing

#### Heated and Cooled Seat Switch

1. Ignition OFF, disconnect the harness connector at the appropriate heated and cooled seat switch.
2. Test for infinite resistance between the signal circuit terminals listed below and the ground circuit terminal 7 with the switch in the open position:

• | Cooled seat switch signal terminal 5

• | Heated seat switch signal terminal 4

⇒ | If not the specified value, replace the heated and cooled seat switch.

3. Test for less than 2 Ω between the signal circuit terminals listed below and the ground circuit terminal 7 with the switch in the closed position:

• | Cooled seat switch signal terminal 5

• | Heated seat switch signal terminal 4

⇒ | If greater than the specified range, replace the heated and cooled seat switch.

4. Connect a 3 A fused jumper wire between the ground circuit terminal 7 and ground.
5. Connect a test lamp between B+ and each control circuit terminal listed below. The appropriate indicator should illuminate.

• | Seat cool mode indicator terminal 9

• | Seat heat mode indicator terminal i

• | Low indicator terminal 6

• | Medium indicator terminal 8

• | High indicator terminal 10

⇒ | If any indicator does not illuminate, replace the heated and cooled seat switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Driver or Passenger Seat Heater Switch Replacement

• | Driver or Passenger Seat Back Cushion Heater Replacement

• | Driver or Passenger Seat Cushion Heater Replacement

• | Driver or Passenger Seat Cushion Ventilation Heating and Cooling Blower Replacement

• | Control Module References for MSM replacement, setup, and programming