HVAC Automatic Climate Control Defaults to Full Cold or Full Hot Despite Controls Being Set to Other Parameters, DTCs B0423, B0228, B3779, B0413, B3782, B0433 (Reprogram HVAC Control Module)

Some customers may comment that the Heating, Ventilation and Air Conditioning (HVAC) automatic climate control system defaults to full hot and/or full cold, despite the HVAC controls being set to other parameters. This condition may not exist during the next ignition cycle and the system may operate normally.

Technicians may find that Diagnostic Trouble Codes (DTCs) B0423, B0228, B3779, B0413, B3782, B0433 have or have not been set.

This condition may be caused by a software anomaly.

Important: If the vehicle is a 2007-2008 GMC Acadia or Saturn OUTLOOK with an additional customer concern of an inaccurate ambient temperature display, then it may be necessary to reprogram the HVAC control module and relocate the ambient air temperature sensor. Refer to bulletin 08-01-39-008 - HVAC Ambient Temperature Sensor Display In Instrument Panel Cluster (IPC) Inaccurate Or Too High for more information.

A revised calibration has been developed to address these conditions. Technicians are to reprogram the HVAC control module using SPS with the latest software available on TIS2WEB. Refer to the HVAC Control Module Programming and Setup procedure in SI for more information. As always make sure your Tech 2® is updated with the latest software version.

Also, clear all DTCs and make sure that B0423, B0228, B3779, B0413, B3782 or B0433 are not current. If DTCs B0423, B0228, B3779, B0413, B3782 or B0433 are set as current, follow normal diagnostic procedures in SI.

For vehicles repaired under warranty, use: