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B2729



DTC B19A3, B19A7, or B2729

DTC Descriptors

DTC B19A3: Driver Seat Cushion Blower Speed Circuit High.
DTC B19A7: Driver Seat Cushion Blower Speed Circuit Short to Ground.
DTC B2729: Driver Seat Cushion Over Temperature.

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.









Circuit/System Description

The heat and cool seat functions for both 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 GMLAN 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.

Conditions for Running the DTC

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

Conditions for Setting the DTC

B13A3
- The CCSM detects a short to B+ on the driver seat cushion blower speed control circuit.

B19A7
- The CCSM detects a short to ground on the driver seat cushion blower speed control circuit.

B2729
- The CCSM detects an open in the seat cushion blower speed control circuit.
- The CCSM detects an open in the seat cushion blower low reference circuit.
- The CCSM detects an open in the seat cushion blower supply voltage circuit.
- The CCSM detects a short to ground on the seat cushion temperature sensor signal circuit for more than 4 seconds.

Action Taken When the DTC Sets

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

Conditions for Clearing the DTC

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

Diagnostic Aids

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.

Circuit/System Verification

Ignition ON, verify the scan tool Seat 1 Cushion Temp parameter is between 0.5-4.73 volts.
-> If not within the specified range, refer to the Seat Cushion Temperature Sensor Test.
-> If the seat cushion temperature parameter displayed correctly on the scan tool, refer to the Seat Cushion Blower Test.

Circuit/System Testing

Seat Cushion Temperature Sensor Test

1. Ignition OFF, disconnect the C2 harness connector at 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.

2. Test for 300 ohms-18K ohms between the signal circuit terminal 7 and the low reference circuit terminal 8.
-> 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 seat cushion ventilation heat and cool module.
-> 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 seat cushion ventilation heat and cool module.
3. Connect the C2 harness connector at the CCSM.
4. Disconnect the harness connector at the seat cushion ventilation heat and cool module.
5. 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 circuits tests normal, replace the CCSM.
6. If all circuits test normal, replace the CCSM.

Seat Cushion Blower Test

1. Ignition OFF, disconnect the harness connector at the seat cushion ventilation heat and cool module.
2. Test for less than 1 ohm 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.
3. Connect a test lamp between the supply voltage circuit terminal 2 and ground.
4. Ignition ON, command the Driver Seat Blower 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 ON, test the supply voltage circuit for a short to voltage. If the circuit tests normal, replace the CCSM.
-> If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open high resistance. If the circuit tests normal, replace the CCSM.
5. Connect a test lamp between the control circuit terminal 7 and ground.
6. Ignition ON, command the Driver Seat Blower 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 ON, test the control circuit for a short to voltage. If the circuits test normal, replace the CCSM.
-> If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit test normal, replace the CCSM.
7. Connect the harness connector at the seat cushion ventilation heat and cool module.
8. Ignition ON, command the Driver Seat Blower Cmd. ON and OFF with a scan tool. The seat cushion blower should turn ON an OFF when changing between the commanded states.
-> If the blower is always OFF, test or replace the seat cushion ventilation heat and cool module.
9. If all circuits test normal, replace the CCSM.

Component Testing

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 hotter or colder 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 hotter or colder 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 supply voltage circuit and the Negative Lead for the ground circuit.

4. Test for 6-9K ohms between blower motor supply voltage 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.




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