DTC Troubleshooting: B121D (89)
DTC B121D or DTC indicator 89: Humidity/In-Car Temperature Sensor Communication Error
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
B121D Humidity/in-car temperature sensor communication error
  

1.
Problem verification:

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 or 89 indicated?

     
YES
     
     
     
Go to step 2.
     
NO
     
     
     
Intermittent failure Check for loose wires or poor connections on the humidity/in-car temperature sensor circuit.?
2.
Humidity/in-car temperature sensor SENSOR 5V line check:

Humidity/in-car temperature sensor SENSOR 5V line check
?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.
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


Is there about 5 V?

     
YES
     
     
     
Go to step 3.
     
NO
     
     
     
Go to step 7.
3.
Open wire check (SENSOR COM line):

Open wire check (SENSOR COM 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
Humidity/in-car temperature sensor 4P connector: disconnected
Test point 1
Climate control unit 32P connector No. 23
Test point 2
Humidity/in-car temperature sensor 4P connector No. 3


Is there continuity?

     
YES
     
     
     
The SENSOR COM wire is OK. Go to step 4.
     
NO
     
     
     
Repair an open in the wire between the climate control unit and the humidity/in-car temperature sensor.?
4.
Climate control unit HUM CLK, HUM DATA lines check 1:

Climate control unit HUM CLK, HUM DATA lines check 1
?1.
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


?2.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
Climate control unit 32P connector: disconnected
Humidity/in-car temperature sensor 4P connector: disconnected
Humidity/in-car temperature sensor 4P connector No. 2 and No. 4: jumped
Test point 1
Climate control unit 32P connector No. 4
Test point 2
Climate control unit 32P connector No. 5

Is there continuity?

     
YES
     
     
     
Go to step 5.
     
NO
     
     
     
Go to step 8.
5.
Climate control unit HUM CLK, HUM DATA lines check 2:

Climate control unit HUM CLK, HUM DATA lines check 2
?1.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
Climate control unit 32P connector: disconnected
Humidity/in-car temperature sensor 4P connector: disconnected
Humidity/in-car temperature sensor 4P connector No. 2 and No. 4: jumped
Test point 1
Climate control unit 32P connector No. 4
Test point 2
Body ground

Is there continuity?

     
YES
     
     
     
Go to step 6.
     
NO
     
     
     
Go to step 9.
6.
Shorted wire check (HUM DATA line):

Shorted wire check (HUM DATA line)
?1.
Disconnect the jumper wire.

?2.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
Climate control unit 32P connector: disconnected
Humidity/in-car temperature sensor 4P connector: disconnected
Test point 1
Climate control unit 32P connector No. 4
Test point 2
Body ground

Is there continuity?

     
YES
     
     
     
Repair a short to ground in the HUM DATA wire between the climate control unit and the humidity/in-car temperature sensor.?
     
NO
     
     
     
Repair a short to ground in the HUM CLK wire between the climate control unit and the humidity/in-car temperature sensor.?
7.
Open wire check (SENSOR 5V line):

Open wire check (SENSOR 5V 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
Humidity/in-car temperature sensor 4P connector: disconnected
Test point 1
Climate control unit 32P connector No. 17
Test point 2
Humidity/in-car temperature sensor 4P connector No. 1


Is there continuity?

     
YES
     
     
     
     
NO
     
     
     
Repair an open in the wire between the climate control unit and the humidity/in-car temperature sensor.?
8.
Open wire check (HUM DATA line):

Open wire check (HUM DATA line)
?1.
Disconnect the jumper wire.

?2.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
Climate control unit 32P connector: disconnected
Humidity/in-car temperature sensor 4P connector: disconnected
Test point 1
Climate control unit 32P connector No. 4
Test point 2
Humidity/in-car temperature sensor 4P connector No. 2


Is there continuity?

     
YES
     
     
     
Repair an open in the HUM CLK wire between the climate control unit and the humidity/in-car temperature sensor.?
     
NO
     
     
     
Repair an open in the HUM DATA wire between the climate control unit and the humidity/in-car temperature sensor.?
9.
Shorted wire check (HUM CLK line to HUM DATA line):

Shorted wire check (HUM CLK line to HUM DATA line)
?1.
Disconnect the jumper wire.

?2.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
Climate control unit 32P connector: disconnected
Humidity/in-car temperature sensor 4P connector: disconnected
Test point 1
Climate control unit 32P connector No. 4
Test point 2
Climate control unit 32P connector No. 5

Is there continuity?

     
YES
     
     
     
Repair a short in the wires between the climate control unit and the humidity/in-car temperature sensor.?
     
NO
     
     
     
Go to step 10.
10.
Climate control unit check:

Climate control unit check
?1.
Reconnect the climate control unit 32P connector.

?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


?3.
Turn the vehicle to the ON mode.

?4.
Press and hold the AUTO and ON/OFF buttons.


Does the mode indicator turn on?

     
YES
     
     
     
     
NO