DTC Troubleshooting: B123F (A-A3), B123F (17) (2020 2021)

DTC B123F or DTC screen A-A3 or DTC indicator 17  : Automatic lighting control unit/sunlight sensor error

*1: Without auto idle stop system

*2: With auto idle stop system

DTCs (AC)

1. Problem verification

   -1. Clear the DTCs 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
   B123F Automatic lighting control unit/sunlight sensor error

   Is DTC B123F or Error on the DTC screen A-A3 (climate control panel without display) or 17 (climate control panel with display) indicated?

   YES *1

   Go to step  3

   YES *2

   Go to step 2

   NO 

   Intermittent failure, the system is OK at this time.

2. Fuse check

   -1. Check the following fuse.

   Fuse	No. B27 (30 A)
   Location	Fuse/relay holder A

   Is the fuse OK?

   YES 

   Go to step 3.

   NO 

   Replace the fuse, and recheck. If the fuse blows again, repair a short in the No. B27 (30 A) fuse circuit.

3. Equipment check 1

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

   -2. Confirm the vehicle have an automatic lighting system.

   Does the combination light switch have an AUTO position?

   YES 

   Go to step 4.

   NO 

   Go to step  5.

4. Equipment check 2

   -1. Confirm the vehicle have an automatic wiper system.

   Does the wiper/washer switch have an AUTO position?

   YES 

   Go to step 5.

   NO 

   Go to step  10.

5. Open wire check (TSUN line)

   -1. Disconnect the following connectors.

   Climate control unit connector A (32P)

   Sunlight sensor 2P connector

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

   Test condition	Vehicle OFF (LOCK) mode
   	Climate control unit connector A (32P): disconnected
   	Sunlight sensor 2P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 10
   Test point 2	Sunlight sensor 2P connector (female terminals) No. 2:

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

   Is there 1.0 Ω or less?

   YES 

   The TSUN wire is not open. Go to step 6.

   NO 

   Repair an open in the TSUN wire.

6. 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
   	Sunlight sensor 2P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 12
   Test point 2	Sunlight sensor 2P connector (female terminals) No. 1:

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

   Is there 1.0 Ω or less?

   YES 

   The SENSOR COM wire is OK. Go to step 7.

   NO 

   Repair an open in the SENSOR COM wire.

7. Shorted wire check (TSUN line)

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

   Test condition	Vehicle OFF (LOCK) mode
   	Climate control unit connector A (32P): disconnected
   	Sunlight sensor 2P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 10
   Test point 2	Body ground

   Is there 1 MΩ or more?

   YES 

   The TSUN wire is not shorted. Go to step 8.

   NO 

   Repair a short to ground in the TSUN wire.

8. Shorted wire check (TSUN line to 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
   	Sunlight sensor 2P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 10
   Test point 2	Climate control unit connector A (32P) No. 12

   Is there 1 MΩ or more?

   YES 

   The TSUN wire and SENSOR COM wire are OK. Go to step 9.

   NO 

   Repair a short in the TSUN wire to SENSOR COM wire.

9. Sunlight sensor check

   -1. Reconnect the following connectors.

   Climate control unit connector A (32P)

   Sunlight sensor 2P connector

   -2. Test the sunlight sensor .

   Is the sunlight sensor OK?

   YES 

   Replace the climate control unit .

   NO 

   Replace the sunlight sensor .

10. Fuse check:
    NOTE: Check for DTCs. If a DTC U1280 or Error on the DTC screen I-A1 (climate control panel without display) or 80 (climate control panel with display) indicated, troubleshoot the DTC first.

    -1. Check the following fuse.

    Fuse	No. A18 (10 A)
    Location	Under-hood fuse/relay box

    Is the fuse OK?

    YES 

    Go to step 11.

    NO 

    Replace the fuse, and recheck. If the fuse blows again, repair a short in the No. A18 (10 A) fuse circuit.

11. Determine possible failure area (B-CAN lines, others)

    -1. Disconnect the following connector.

    Automatic lighting control unit-sensor 5P connector

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

    Test condition	Vehicle OFF (LOCK) mode
    	Automatic lighting control unit-sensor 5P connector: disconnected
    Test point 1	Automatic lighting control unit-sensor 5P connector No. 3
    Test point 2	Automatic lighting control unit-sensor 5P connector No. 4

    Is there battery voltage?

    YES 

    Go to step 12.

    NO 

    Go to step  15.

12. Open wire check (B-CAN_H line)

    -1. Disconnect the following connector.

    Climate control unit connector A (32P)

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

    Test condition	Vehicle OFF (LOCK) mode
    	Automatic lighting control unit-sensor 5P connector: disconnected
    	Climate control unit connector A (32P): disconnected
    Test point 1	Automatic lighting control unit-sensor 5P connector No. 1
    Test point 2	Climate control unit connector A (32P) No. 25

    Is there 1.0 Ω or less?

    YES 

    The B-CAN_H wire is OK. Go to step 13.

    NO 

    Repair an open in the B-CAN_H wire.

13. Open wire check (B-CAN_L line)

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

    Test condition	Vehicle OFF (LOCK) mode
    	Automatic lighting control unit-sensor 5P connector: disconnected
    	Climate control unit connector A (32P): disconnected
    Test point 1	Automatic lighting control unit-sensor 5P connector No. 2
    Test point 2	Climate control unit connector A (32P) No. 8

    Is there 1.0 Ω or less?

    YES 

    The B-CAN_L wire is OK. Go to step 14.

    NO 

    Repair an open in the B-CAN_L wire.

14. DTC check

    -1. Reconnect the following connectors.

    Automatic lighting control unit-sensor 5P connector

    Climate control unit connector A (32P)

    -2. Clear the DTC with the HDS.

    -3. Turn the vehicle to the OFF (LOCK) mode then the ON mode.

    -4. Wait for at least 8 seconds.

    -5. Do the Self-Diagnostic Function with the climate control unit .

    -6. Check for DTCs.

    DTC Description	DTC
    B123F Automatic lighting control unit/sunlight sensor error
    U128D Climate Control Unit Lost communication with gauge control module

    Is DTC B123F or Error on the DTC screen A-A3 (climate control panel without display) or 17 (climate control panel with display) and DTC U128D or Error on the DTC screen I-A2 (climate control panel without display) or 83 (climate control panel with display) indicated?

    YES 

    Replace the climate control unit .

    NO 

    Replace the automatic lighting control unit-sensor .

15. Open wire check (+B BACK UP *1, +B BACKUP2 SUB *2 line):-1.

    Measure the voltage between test points 1 and 2.

    Test condition	Vehicle OFF (LOCK) mode
    	Automatic lighting control unit-sensor 5P connector: disconnected
    Test point 1	Automatic lighting control unit-sensor 5P connector No. 4
    Test point 2	Body ground

    Is there battery voltage?

    YES 

    Check for an open in the GND wire between the automatic lighting control unit-sensor and body ground. If the wire is OK, check for poor ground at G402.

    NO 

    Repair an open in the +B BACK UP *1, +B BACKUP2 SUB *2 wire.