DTC Troubleshooting: B121B (B-B2), B121B (4A)

DTC B121B or DTC screen B-B2 or DTC indicator 4A  : A short in the mode control motor circuit

NOTE:  If other short circuit DTCs are indicated at the same time, there may be an open or short to body ground in the power (5 V) circuit.

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
   B121B A short in the mode control motor circuit

   Is DTC B121B or Error on the DTC screen B-B2 (climate control panel without display) or 4A (climate control panel with display) indicated?

   YES 

   Go to step 2.

   NO 

   Intermittent failure. Check for loose wires or poor connections on the mode control motor circuit.

2. Determine possible failure area (S5V line, others)

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

   -2. Disconnect the following connector.

   Mode control motor 5P connector

   -3. Turn the vehicle to the ON mode.

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

   Test condition	Vehicle ON mode
   	Mode control motor 5P connector: disconnected
   Test point 1	Mode control motor 5P connector (female terminals) No. 3:
   Test point 2	Body ground

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

   Is there about 5 V?

   YES 

   The S5V wire is OK. Go to step 3.

   NO 

   Go to step  4.

3. Determine possible failure area (mode control motor, others)

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

   Test condition	Vehicle ON mode
   	Mode control motor 5P connector: disconnected
   Test point 1	Mode control motor 5P connector (female terminals) No. 2:
   Test point 2	Body ground

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

   Is there about 5 V?

   YES 

   Replace the mode control motor .

   NO 

   Go to step  6.

4. Open wire check (S5V line)

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

   Test condition	Vehicle ON mode
   	Mode control motor 5P connector: disconnected
   Test point 1	Climate control unit connector B (24P) No. 1
   Test point 2	Body ground

   Is there about 5 V?

   YES 

   Repair an open in the S5V wire.

   NO 

   Go to step 5.

5. Shorted wire check (S5V line)

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

   -2. Disconnect the following connector.

   Climate control unit connector B (24P)

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

   Test condition	Vehicle OFF (LOCK) mode
   	Climate control unit connector B (24P): disconnected
   	Mode control motor 5P connector: disconnected
   Test point 1	Climate control unit connector B (24P) No. 1
   Test point 2	Body ground

   Is there continuity?

   YES 

   Repair a short to ground in the S5V wire.

   NO 

   Replace the climate control unit .

6. Shorted wire check (MDD-P line)

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

   -2. Disconnect the following connector.

   Climate control unit connector B (24P)

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

   Test condition	Vehicle OFF (LOCK) mode
   	Climate control unit connector B (24P): disconnected
   	Mode control motor 5P connector: disconnected
   Test point 1	Climate control unit connector B (24P) No. 5
   Test point 2	Body ground

   Is there continuity?

   YES 

   Repair a short to ground in the MDD-P wire.

   NO 

   Replace the climate control unit .