DTC Troubleshooting: B121D (A-B6), B121D (89) (2020 2021)

DTC B121D or DTC screen A-B6 or DTC indicator 89  : Humidity/In-Car Temperature Sensor Communication Error

1. Problem verification

   -1. Clear the DTC with the HDS.

   -2. Turn the vehicle to the OFF (LOCK) mode and 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
   B121D Humidity/in-car temperature sensor communication error

   Is DTC B121D, Error on the DTC screen A-B6 (climate control panel without display), or 89 (climate control panel with display) indicated?

   YES: Climate control panel without display

   Go to step 2.

   YES: Climate control panel with display

   Go to step  4.

   NO 

   Intermittent failure. Check for loose wires or poor connections on the humidity/in-car temperature sensor circuit.

2. Climate control unit check 1

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

   -2. Disconnect the following connector.

   Humidity/in-car temperature sensor 4P connector

   -3. Turn the vehicle to the ON mode.

   -4. While pressing the WINDSHIELD DEFROST button, press and hold the ON/OFF button for 10 seconds or more.

   Is Normal on the DTC screen A-B7 indicated?

   YES 

   Go to step  7.

   NO 

   Go to step 3.

3. Climate control unit check 2

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

   -2. Connect terminals A and B with a jumper wire.

   Terminal A	Humidity/in-car temperature sensor 4P connector No. 2:
   Terminal B	Humidity/in-car temperature sensor 4P connector No. 4:

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

   -3. Turn the vehicle to the ON mode.

   -4. While pressing the WINDSHIELD DEFROST button, press and hold the ON/OFF button for 10 seconds or more.

   Is Normal on the DTC screen A-B7 indicated?

   YES 

   Go to step  6.

   NO 

   Go to step  8.

4. Climate control unit check 1

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

   -2. Disconnect the following connector.

   Humidity/in-car temperature sensor 4P connector

   -3. Turn the vehicle to the ON mode.

   -4. While pressing the WINDSHIELD DEFROST button, press and hold the ON/OFF button for 10 seconds or more.

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

   Does the MODE indicator turn on?

   YES 

   Go to step  7.

   NO 

   Go to step 5.

5. Climate control unit check 2

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

   -2. Connect terminals A and B with a jumper wire.

   Terminal A	Humidity/in-car temperature sensor 4P connector No. 2:
   Terminal B	Humidity/in-car temperature sensor 4P connector No. 4:

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

   -3. Turn the vehicle to the ON mode.

   -4. While pressing the WINDSHIELD DEFROST button, press and hold the ON/OFF button for 10 seconds or more.

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

   Does the MODE indicator turn on?

   YES 

   Go to step 6.

   NO 

   Go to step  8.

6. Determine possible failure area (humidity/in-car temperature sensor, others)

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

   -2. Disconnect the jumper wire.

   -3. Turn the vehicle to the ON mode.

   -4. Measure the voltage between test points 1 and 2.

   Test condition	Vehicle ON mode
   	Humidity/in-car temperature sensor 4P connector: disconnected
   Test point 1	Humidity/in-car temperature sensor 4P connector No. 1:
   Test point 2	Body ground

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

   Is there about 5 V?

   YES 

   Replace the humidity/in-car temperature sensor .

   NO 

   Go to step  12.

7. Shorted wire check (HUM DATA line to HUM CLK line)

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

   -2. Disconnect the following connector.

   Climate control unit connector A (32P)

   -3. Measure the resistance between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	Climate control unit connector A (32P): disconnected
   	Humidity/in-car temperature sensor 4P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 7
   Test point 2	Climate control unit connector A (32P) No. 24

   Is there 1 MΩ or more?

   YES 

   Replace the climate control unit .

   NO 

   Repair a short in the HUM DATA wire to HUM CLK wire.

8. Open wire check (HUM DATA line)

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

   -2. Disconnect the jumper wire.

   -3. Disconnect the following connector.

   Climate control unit connector A (32P)

   -4. Measure the resistance between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	Climate control unit connector A (32P): disconnected
   	Humidity/in-car temperature sensor 4P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 7
   Test point 2	Humidity/in-car temperature sensor 4P connector No. 2:

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

   Is there 1.0 Ω or less?

   YES 

   The HUM DATA wire is not open. Go to step 9.

   NO 

   Repair an open in the HUM DATA wire.

9. Open wire check (HUM CLK line)

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

   Test condition	Vehicle OFF (LOCK) mode
   	Climate control unit connector A (32P): disconnected
   	Humidity/in-car temperature sensor 4P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 24
   Test point 2	Humidity/in-car temperature sensor 4P connector No. 4:

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

   Is there 1.0 Ω or less?

   YES 

   The HUM CLK wire is not open. Go to step 10.

   NO 

   Repair an open in the HUM CLK wire.

10. Shorted wire check (HUM DATA line)

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

    Test condition	Vehicle OFF (LOCK) mode
    	Climate control unit connector A (32P): disconnected
    	Humidity/in-car temperature sensor 4P connector: disconnected
    Test point 1	Climate control unit connector A (32P) No. 7
    Test point 2	Body ground

    Is there 1 MΩ or more?

    YES 

    The HUM DATA wire is OK. Go to step 11.

    NO 

    Repair a short to ground in the HUM DATA wire.

11. Shorted wire check (HUM CLK line)

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

    Test condition	Vehicle OFF (LOCK) mode
    	Climate control unit connector A (32P): disconnected
    	Humidity/in-car temperature sensor 4P connector: disconnected
    Test point 1	Climate control unit connector A (32P) No. 24
    Test point 2	Body ground

    Is there 1 MΩ or more?

    YES 

    Replace the climate control unit .

    NO 

    Repair a short to ground in the HUM CLK wire.

12. Open wire check (S 5V line)

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

    -2. Disconnect the following connector.

    Climate control unit connector A (32P)

    -3. Measure the resistance between test points 1 and 2.

    Test condition	Vehicle OFF (LOCK) mode
    	Climate control unit connector A (32P): disconnected
    	Humidity/in-car temperature sensor 4P connector: disconnected
    Test point 1	Climate control unit connector A (32P) No. 26
    Test point 2	Humidity/in-car temperature sensor 4P connector No. 1:

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

    Is there 1.0 Ω or less?

    YES 

    The S 5V line is not open. Go to step 13.

    NO 

    Repair an open in the S 5V wire.

13. Open wire check (SENSOR COM line)

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

    Test condition	Vehicle OFF (LOCK) mode
    	Climate control unit connector A (32P): disconnected
    	Humidity/in-car temperature sensor 4P connector: disconnected
    Test point 1	Climate control unit connector A (32P) No. 12
    Test point 2	Humidity/in-car temperature sensor 4P connector No. 3:

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

    Is there 1.0 Ω or less?

    YES 

    The SENSOR COM wire is OK. Go to step 14.

    NO 

    Repair an open in the SENSOR COM wire.

14. Shorted wire check (S 5V line)

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

    Test condition	Vehicle OFF (LOCK) mode
    	Climate control unit connector A (32P): disconnected
    	Humidity/in-car temperature sensor 4P connector: disconnected
    Test point 1	Climate control unit connector A (32P) No. 26
    Test point 2	Body ground

    Is there 1 MΩ or more?

    YES 

    Replace the climate control unit .

    NO 

    Repair a short to ground in the S 5V wire.