Subaru Legacy BN/BS (2015-2019) Service Manual: Dtc u0028 heater control panel communication error

Subaru Legacy BN/BS (2015-2019) Service Manual / Hvac system (diagnostics) / Diagnostic procedure with diagnostic trouble code (dtc) / Dtc u0028 heater control panel communication error

DTC DETECTING CONDITION:

UART communication failure

TROUBLE SYMPTOM:

• Unable to operate A/C.

• DTC “U0028” HEATER CONTROL PANEL COMMUNICATION ERROR was detected.

WIRING DIAGRAM:

Air conditioning system Air Conditioning System > WIRING DIAGRAM

STEP	CHECK	YES	NO
1.CHECK CONNECTOR. Check poor contact of the power supply circuit connectors, A/C control panel connector and A/C CM connector.	Is there poor contact-	Repair the connector.	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC U0028 HEATER CONTROL PANEL COMMUNICATION ERROR
2.CHECK FUSE. 1) Turn the ignition switch to OFF. 2) Remove the fuses No. 19 and 26 from the main fuse box or fuse & relay box. 3) Check the condition of fuse. Relay and Fuse	Is the fuse blown out-	Replace the fuse.	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC U0028 HEATER CONTROL PANEL COMMUNICATION ERROR
3.CHECK A/C CONTROL PANEL POWER CIRCUIT. 1) Remove the A/C control panel. 2) Disconnect the A/C control panel connector. 3) Measure the voltage between A/C control panel connector terminal and chassis ground after turning the ignition switch to ON. Connector & terminal (i88) No. 10 (+) — Chassis ground (−): (i88) No. 4 (+) — Chassis ground (−):	Is the voltage 10 V or more-	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC U0028 HEATER CONTROL PANEL COMMUNICATION ERROR	Check for open or short circuit in the harness between A/C control panel and fuse.
4.CHECK A/C CONTROL PANEL GROUND CIRCUIT. Measure the resistance of harness between A/C control panel and chassis ground after turning the ignition switch to OFF. Connector & terminal (i88) No. 14 — Chassis ground:	Is the resistance less than 10 --	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC U0028 HEATER CONTROL PANEL COMMUNICATION ERROR	Repair the harness for ground line.
5.CHECK COMMUNICATION CIRCUIT HARNESS. 1) Disconnect the connector from A/C control panel and A/C CM. 2) Using a tester, check for continuity between the harness terminals. Connector & terminal (i181) No. 11 — (i88) No. 7: (i181) No. 12 — (i88) No. 15:	Is there continuity-	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC U0028 HEATER CONTROL PANEL COMMUNICATION ERROR	Repair or replace the open circuit of harness.
6.CHECK HARNESS. Using a tester, check continuity between terminals. Connector & terminal (i181) No. 11 — No. 12: (i181) No. 11 — Chassis ground: (i181) No. 12 — Chassis ground:	Is there continuity-	Repair or replace the short circuit of the harness.	Replace the A/C control panel. Control Panel > REMOVAL

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