DTC U129B (Without Auto Idle Stop System)

DTC U129B  : Lost Communication with Seat Heater Control Unit (Second Row Seat) (Climate Control Unit)

DTCs (AC)

1. Problem verification

   - 1. Clear the DTCs with the HDS.

   - 2. Turn the vehicle to the OFF (LOCK) mode then the ON mode.

   - 3. Do the Self-Diagnostic Function with the HDS or the climate control unit.

   - 4. Check for DTCs.

   DTC Description	DTC
   U129B Lost communication with seat heater control unit (second row seat) (climate control unit)

   Is DTC U129B indicated?

   YES 

   Go to step 2.

   NO 

   Intermittent failure, the system is OK at this time. Check for loose or poor connections.

2. Determine possible failure area (second row seat heater control unit power and ground, B-CAN lines)

   - 1. Select B-CAN Control Units Information from the Body Electrical System Select menu, then select Check Connected Control Units.

   - 2. Check the DETECT/Not available information of the Rear Seat Heater Control Unit.

   Is DETECT indicated?

   YES 

   Go to step 3.

   NO 

   Go to step 4.

3. Open wire check (B-CAN_H line)

   - 1. Turn the vehicle to the OFF (LOCK) mode.

   - 2. Disconnect the following connectors.

   Second row seat heater control unit 14P connector

   Climate control unit connector A (32P)

   - 3. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	Second row seat heater control unit 14P connector: disconnected
   	Climate control unit connector A (32P): disconnected
   Test point 1	Second row seat heater control unit 14P connector No. 11
   Test point 2	Climate control unit connector A (32P) No. 23 - Refer to: Climate Control Unit Connector For Inputs and Outputs (2019 2020 2021), or Climate Control Unit Connector For Inputs and Outputs (2016 2017 2018)

   Courtesy of HONDA, U.S.A., INC.

   Is there continuity?

   YES 

   Repair an open or poor connection in the B-CAN_L wire between the climate control unit and the second row seat heater control unit.

   NO 

   Repair an open or poor connection in the B-CAN_H wire between the climate control unit and the second row seat heater control unit.

4. Fuse check

   - 1. Turn the vehicle to the OFF (LOCK) mode.

   - 2. Check the following fuse.

   Fuse	No. C29 (7.5 A)
   Location	Under-dash fuse/relay box

   Is the fuse OK?

   YES 

   Go to step 5.

   NO 

   Replace the fuse, and recheck. If the fuse blow again, repair a short in the No. C29 (7.5 A) fuse circuit.

5. Open wire check (+B RR H/SEAT line)

   - 1. Disconnect the following connector.

   Second row seat heater control unit 14P connector

   - 2. Measure the voltage between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	Second row seat heater control unit 14P connector: disconnected
   Test point 1	Second row seat heater control unit 14P connector No. 2
   Test point 2	Body ground

   Courtesy of HONDA, U.S.A., INC.

   Is there battery voltage?

   YES 

   The +B RR H/SEAT wire is OK. Go to step 6.

   NO 

   Repair an open in the +B RR H/SEAT wire.

6. Open wire check (IG1 METER(7.5 A) line)

   - 1. Turn the vehicle to the ON mode.

   - 2. Measure the voltage between test points 1 and 2.

   Test condition	Vehicle ON mode
   	Second row seat heater control unit 14P connector: disconnected
   Test point 1	Second row seat heater control unit 14P connector No. 9
   Test point 2	Body ground

   Courtesy of HONDA, U.S.A., INC.

   Is there battery voltage?

   YES 

   The IG1 METER(7.5 A) wire is OK. Go to step 7.

   NO 

   Repair an open in the IG1 METER(7.5 A) wire.

7. Open wire check (GND(HTR UNIT) lines)

   - 1. Turn the vehicle to the OFF (LOCK) mode.

   - 2. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	Second row seat heater control unit 14P connector: disconnected
   Test circuit 1
   Test point 1	Second row seat heater control unit 14P connector No. 4
   Test point 2	Body ground

   Test circuit 2
   Test point 1	Second row seat heater control unit 14P connector No. 14
   Test point 2	Body ground

   Courtesy of HONDA, U.S.A., INC.

   Is there continuity?

   YES 

   The GND(HTR UNIT) wires are OK. Go to step 8

   NO 

   Check for an open in the wire(s) between the second row seat heater control unit and body ground. If the wire(s) is OK, check for poor ground at G603.

8. Open wire check (B-CAN_H line)

   - 1. Disconnect the following connector.

   Climate control unit connector A (32P)

   - 2. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	Second row seat heater control unit 14P connector: disconnected
   	Climate control unit connector A (32P): disconnected
   Test point 1	Second row seat heater control unit 14P connector No. 11
   Test point 2	Climate control unit connector A (32P) No. 23 - Refer to: Climate Control Unit Connector For Inputs and Outputs (2019 2020 2021), or Climate Control Unit Connector For Inputs and Outputs (2016 2017 2018)

   Courtesy of HONDA, U.S.A., INC.

   Is there continuity?

   YES 

   Repair an open or poor connection in the B-CAN_L wire between the climate control unit and the second row seat heater control unit.

   NO 

   Repair an open or poor connection in the B-CAN_H wire between the climate control unit and the second row seat heater control unit.