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Disconnect climate control unit connector A (32P) and the audio-HVAC display unit 12P connector.
Check for continuity between the following terminals of climate control unit connector A (32P) and the audio-HVAC display unit 12P connector.
32P: 12P:

No. 3 No. 7

No. 4 No. 8

Fig 1: Checking Continuity Between Terminals Of Climate Control Unit Connector And Audio-HVAC Display Unit 12P Connector
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES - Go to step 3.

NO - Repair an open in the wire between climate control unit connector A (32P) and the audio-HVAC display unit 12P connector.
Check for continuity between body ground and climate control unit connector A (32P) terminals No. 3 and No. 4 individually.

Fig 2: Checking Continuity Between Body Ground And Climate Control Unit Connector Terminals No. 3 And No. 4
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES - Repair a short to body ground in the wire between climate control unit connector A (32P) and the audio-HVAC display unit 12P connector.

NO - Go to step 4.
Reconnect climate control unit connector A (32P).
Connect audio-HVAC display unit 12P connector terminals No. 7 and No. 8 with a jumper wire.

Fig 3: Connecting Audio-HVAC Display Unit 12P Connector Terminals No. 7 And No. 8 With Jumper Wire
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Turn the ignition switch to ON (II).
Press and hold the front DEF button and OFF button.
Is the front DEF button LED blinking?

YES - The audio-HVAC display unit is faulty, replace the audio-HVAC display unit (see AUDIO-HVAC DISPLAY UNIT REMOVAL/INSTALLATION ).

NO - The climate control unit is faulty, replace the climate control unit (see CLIMATE CONTROL UNIT REMOVAL/INSTALLATION ).