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 ignition switch to LOCK (0) and then back to ON (II), or press the engine start/stop button to select the OFF 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.
Open wire check (S 5V/S5V line):

Open wire check (S 5V/S5V line)
?1.
Turn the ignition switch to LOCK (0), or press the engine start/stop button to select the OFF mode.

?2.
Disconnect the following connectors.

?3.
Check for continuity between test points 1 and 2.
Test condition
IG LOCK (0) or OFF mode
Climate control unit 32P connector: disconnected
Mode control motor 7P connector: disconnected
Test circuit
S 5V/S5V
Test point 1
Climate control unit 32Ponnector No. 24 (BLK)
Test point 2
Mode control motor 7P connector No. 1 (BLK)


Is there continuity?

     
YES
     
     
     
The S 5V/S5V wire is not open. Go to step 3.
     
NO
     
     
     
Repair an open in the wire between the climate control unit and the mode control motor.?
3.
Shorted wire check (MDD-P/MODE-P line to SENSOR COM/SENS-COM line):

Shorted wire check (MDD-P/MODE-P line to SENSOR COM/SENS-COM line)
?1.
Check for continuity between test points 1 and 2.
Test condition
IG LOCK (0) or OFF mode
Climate control unit 32P connector: disconnected
Mode control motor 7P connector: disconnected
Test circuit
MDD-P, SENSOR COM
Test point 1
Climate control unit 32P connector No. 12 (GRN)
Test point 2
Climate control unit 32P connector No. 22 (BLU)


Is there continuity?

     
YES
     
     
     
Repair a short in the wires between the climate control unit and the mode control motor.?
     
NO
     
     
     
The MDD-P/MODE-P wire to SENSOR COM/SENS-COM wire are not shorted. Go to step 4.
4.
Shorted wire check (MDD-P/MODE-P line):

Shorted wire check (MDD-P/MODE-P line)
?1.
Check for continuity between test points 1 and 2.
Test condition
IG LOCK (0) or OFF mode
Climate control unit 32P connector: disconnected
Mode control motor 7P connector: disconnected
Test circuit
MDD-P
Test point 1
Climate control unit 32P connector No. 12 (GRN)
Test point 2
Body ground


Is there continuity?

     
YES
     
     
     
Repair a short to body ground in the wire between the climate control unit and the mode control motor.?
     
NO
     
     
     
The MDD-P/MODE-P wire is OK. Go to step 5.
5.
Mode control motor internal resistance check (S5V and SENS-COM):

Mode control motor internal resistance check (S5V and SENS-COM)
?1.
Measure the resistance between test points 1 and 2.
Test condition
IG LOCK (0) or OFF mode
Climate control unit 32P connector: disconnected
Mode control motor 7P connector: disconnected
Test circuit
S5V, SENS-COM
Test point 1
Mode control motor No. 1
Test point 2
Mode control motor No. 3


Is the resistance 6 k?1.8 k??

     
YES
     
     
     
Go to step 6.
     
NO
     
     
     
6.
Mode control motor internal resistance check (MDD-P and SENSOR COM):

Mode control motor internal resistance check (MDD-P and SENSOR COM)
?1.
Reconnect the mode control motor 7P connector.

?2.
Connect the battery power and ground to terminals A and B, then reverse the connections.
Terminal A
Climate control unit 32P connector No. 4 (WHT)
Terminal B
Climate control unit 32P connector No. 5 (GRN)

NOTE: Incorrectly applying power and ground to the motor will damage it. Follow the instructions carefully. When the motor stops running, disconnect battery power immediately.


?3.
Measure the resistance between test points 1 and 2.
Test condition
IG LOCK (0) or OFF mode
Climate control unit 32P connector: disconnected
Test circuit
MDD-P, SENSOR COM
Test point 1
Climate control unit 32P connector No. 12 (GRN)
Test point 2
Climate control unit 32P connector No. 22 (BLU)

NOTE: Continuity between MDD-P and SENSOR COM may disappear when the motor is turned to the stop. Usually the climate control unit does not turn the motor to the stop.


Does resistance change between about 0?6 k?1.8 k??

     
YES
     
     
     
     
NO