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Tahoe / Yukon Service Manual

DTC B187A-B187D

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. DTC Descriptors DTC B187B Left Rear Seat Cushion Temperature Sensor Signal DTC B187D Right Rear Seat Cushion Temperature Sensor Signal Symptom Byte Information: Symptom Byte List Diagnostic Fault Information

Circuit Number Circuit Function Short to Ground Open/High Resistance Short to Voltage Signal Performan
6740 B+ U0247 U0247 — —
5740 B+ 1 1 — —
7047 Signal B187B:16 B187B:17 B187B:17 —
7048 Low Reference — B187B:17 — —
7053 Signal B187D:16 B187D:17 B187D:17 —
7054 Low Reference — B187D:17 — —
1450 Ground — U0247 — —
1. Left rear heated seat is inoperative

Circuit/System Description The right rear and left rear heated seats switches are located within the A34 Heater and Air Conditioning Auxiliary Control. To operate the heated seats the engine must be running. When a heated seat switch is pressed, a serial data message is sent from the A34 Heater and Air Conditioning Auxiliary Control to the K9 Body Control Module (BCM) indicating the heated seat command. The BCM serves as the heated seat system master to determine the requested operating mode. The BCM then sends a LIN bus serial data message to the K29RV Rear Seat Heater Vent Control Module indicating the heated seat command. In response to this message, the K29RV Rear Seat Heater Vent Control Module attempts to drive the appropriate seat heating elements per the BCM command. The BCM also controls the seat temperature and mode indicators, via the serial data line, used to provide the operator with feedback as to the operating status of the system. The K29RV Rear Seat Heater Vent Control Module controls heated seat operation for the driver and passenger seats. When active, power is applied to the seat cushion and back heater elements through a common pulse width modulated (PWM) voltage supply control circuit. Each individual heater element is switched to ground by the module through a common low side drive control circuit. The seat back and cushion temperature sensors (thermistors) are packaged with the seat heating elements located just under the seat covers. The K29RV Rear Seat Heater Vent Control Module supplies each temperature sensor with a 5 V reference signal circuit and a low reference circuit. The module monitors the voltage from the signal circuit to determine the temperature of the seat. The temperature sensor varies in resistance based on the temperature of the heating element causing the signal voltage to change. Once the module senses the seat reached the set temperature, it will then begin regulate the current flow through the heater elements in order to maintain the desired seat temperature based on the feedback voltage from the sensor. Conditions for Running the DTC Engine ON. Heated Seat System ON. Conditions for Setting the DTC B187B:16, B187D:16 The rear seat heater vent control module detects low voltage on a thermistor signal circuit. B187B:17, B187D:17 The rear seat heater vent control module detects high voltage on a thermistor signal circuit. Action Taken When the DTC Sets The seat heater control module will disable all heated seat functions. Conditions for Clearing the DTC The DTC clears when the diagnostic runs and passes. The history DTC will clear after 40 consecutive fault-free ignition cycles have occurred. Diagnostic Aids A short to ground on either the seat cushion or seat back temperature sensor signal circuit will cause the heated seat function to be inoperative for that seat. The following faults will cause a degraded heated seat operation for both the seat back and seat cushion. – An open or a short to voltage on either the seat cushion or seat back temperature sensor signal circuit. – An open in either the seat cushion or seat back temperature sensor low reference circuit. – A fault in either the seat cushion or seat back temperature sensor. Reference Information Schematic Reference Heated/Cooled Seat Schematics Connector End View Reference Master Electrical Component List Description and Operation Rear Heated Seats 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.
  2. Verify that no other DTCs are set for the heated seat system, besides B187B or B187D. ⇒ If any other DTCs are set for the heated seat system Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If no other DTCs are set
  3. Clear the DTCs.
  4. Verify DTC B187B or B187D is not set. ⇒ If DTC B187B is set Refer to Circuit/System Testing — B187B ⇒ If DTC B187D is set Refer to Circuit/System Testing — B187D ⇓ If no DTCs are set
  5. A fault is currently not present and may be an intermittent condition. Circuit/System Testing B187B
  1. Ignition OFF, disconnect the connector at E14F Seat Heating Element - Left Rear Cushion. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 40 Ω between the low reference circuit terminal 3 and ground. ⇒ If 40 Ω or greater 2.1. Test circuit 7048 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 2.2. Replace the K29RV Rear Seat Heater Vent Control Module. ⇓ If less than 40 Ω
  3. Ignition ON.
  4. Test for 4.8–5.2 V between the signal circuit terminal 2 and ground. ⇒ If less than 4.8 V 4.1. Test circuit 7047 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 4.2. Test circuit 7047 for an open/high resistance ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 4.3. Replace the K29RV Rear Seat Heater Vent Control Module. ⇒ If greater than 5.2 V 4.1. Test circuit 7047 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found 4.2. Replace the K29RV Rear Seat Heater Vent Control Module. ⇓ If between 4.8–5.2 V
  5. Ignition OFF, connect the connector at the E14F Seat Heating Element - Left Rear Cushion. Disconnect the X2 connector at the K29RV Rear Seat Heater Vent Control Module.
  6. Test for 500 Ω–300 kΩ between the signal circuit terminal 6 and the low reference circuit terminal 1. ⇒ If not between 500 Ω–300 kΩ 6.1. Replace the E14F Seat Heating Element - Left Rear Cushion. ⇓ If between 500 Ω–300 kΩ
  7. Replace the K29RV Rear Seat Heater Vent Control Module. B187D
  1. Ignition OFF, disconnect the connector at E14H Seat Heating Element - Right Rear Cushion. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 40 Ω between the low reference circuit terminal 3 and ground. ⇒ If 40 Ω or greater 2.1. Test circuit 7054 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 2.2. Replace the K29RV Rear Seat Heater Vent Control Module. ⇓ If less than 40 Ω
  3. Ignition ON.
  4. Test for 4.8–5.2 V between the signal circuit terminal 2 and ground. ⇒ If less than 4.8 V 4.1. Test circuit 7053 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 4.2. Test circuit 7053 for an open/high resistance ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 4.3. Replace the K29RV Rear Seat Heater Vent Control Module. ⇒ If greater than 5.2 V 4.1. Test circuit 7053 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found 4.2. Replace the K29RV Rear Seat Heater Vent Control Module. ⇓ If between 4.8–5.2 V
  5. Ignition OFF, connect the connector at the E14H Seat Heating Element - Right Rear Cushion. Disconnect the X2 connector at the K29RV Rear Seat Heater Vent Control Module.
  6. Test for 500 Ω–300 kΩ between the signal circuit terminal 6 and the low reference circuit terminal 1. ⇒ If not between 500 Ω–300 kΩ 6.1. Replace the E14HF Seat Heating Element - Right Rear Cushion. ⇓ If between 500 Ω–300 kΩ
  7. Replace the K29RV Rear Seat Heater Vent Control Module. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Control Module References for K29RV Rear Seat Heater Vent Control Module replacement, programming, and setup.