DTC U128D: Lost Communication with Gauge Control Module (HVAC Control Unit)

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NOTE: If you are troubleshooting multiple DTCs, be sure to follow the instructions in B-CAN System Diagnosis Test Mode A (see TROUBLESHOOTING - B-CAN SYSTEM DIAGNOSIS TEST MODE A ).

Clear the DTCs with the HDS.
Turn the ignition switch to LOCK (0), and then back to ON (II).
Do the Self-Diagnostic Function with the HDS (see HOW TO USE THE SELF-DIAGNOSTIC FUNCTION WITH THE HDS ).
Check for DTCs.
Is DTC U128D indicated?

YES -Go to step 5.

NO -The system is OK at this time. Check for loose wires or poor connections on the gauge control module and HVAC control unit circuit.
Select B-CAN Control Units Information in the BODY ELECTRICAL menu.
Select Check Connected Control Units in the B-CAN Control Units Information menu.
Is the gauge control module detected?

YES -Substitute a known-good HVAC control unit, and recheck. If the symptom/indication goes away, replace the original HVAC control unit (see HVAC CONTROL UNIT REMOVAL/INSTALLATION ).

NO -Go to step 7.
Disconnect the gauge control module 32P connector.
Disconnect the HVAC control unit 28P connector.

Check for continuity between the following terminals of the gauge control module 32P connector and the HVAC control unit 28P connector.

CONNECTOR TERMINAL REFERENCE CHART

32P:	28P:
No. 29	No. 26
No. 30	No. 28

Fig 1: Checking Continuity Between Gauge Control Module 32P Connector And HVAC Control Unit 28P Connector Terminals

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES -Go to the gauge control module input test (see GAUGE CONTROL MODULE INPUT TEST ).

NO -Repair an open in the wire between the HVAC control unit and the gauge control module.