DTC Troubleshooting: B121B (4A)
DTC B121B 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.

DTC Description
DTC
B121B A Short in the Mode Control Motor Circuit
  

1.
Problem verification:

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 4A 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 (S 5V/S5V line, others):

Determine possible failure area (S 5V/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 No. 1
Test point 2
Body ground


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):

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 No. 2
Test point 2
Body ground


Is there about 5 V?

     
YES
     
     
     
     
NO
     
     
     
Go to step 6.
4.
Open wire check (S 5V/S5V line):

Open wire check (S 5V/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 32P connector No. 24
Test point 2
Body ground

Is there about 5 V?

     
YES
     
     
     
Repair an open in the wire between the climate control unit and the mode control motor.?
     
NO
     
     
     
The S 5V/S5V wire is not open. Go to step 5.
5.
Shorted wire check (S 5V/S5V line):

Shorted wire check (S 5V/S5V line)
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Disconnect the following connector.
Climate control unit 32P connector

?3.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
Climate control unit 32P connector: disconnected
Mode control motor 5P connector: disconnected
Test point 1
Climate control unit 32P connector No. 24
Test point 2
Body ground

Is there continuity?

     
YES
     
     
     
Repair a short to ground in the wire between the climate control unit and the mode control motor.?
     
NO
     
     
     
The S 5V/S5V wire is not shorted. Replace the climate control unit.?
6.
Shorted wire check (MDD-P line):

Shorted wire check (MDD-P line)
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Disconnect the following connector.
Climate control unit 32P connector

?3.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
Climate control unit 32P connector: disconnected
Mode control motor 5P connector: disconnected
Test point 1
Climate control unit 32P connector No. 27
Test point 2
Body ground

Is there continuity?

     
YES
     
     
     
Repair a short to ground in the wire between the climate control unit and the mode control motor.?
     
NO
     
     
     
The MDD-P wire is not shorted. Replace the climate control unit.?