Unable to Control Rear HVAC Temperature or Modes, Intermittent Ticking Noise from Rear HVAC Actuators or Rear HVAC DTCs B0434 or B3764 (Replace Auxiliary HVAC Control Module)

This bulletin is being revised to correct one of the blower motor control module part numbers. Please discard Corporate Bulletin Number 06-01-39-015 (Section 01 -- HVAC).

Some customers may comment on one or more of the following conditions:

Technicians may find that Diagnostic Trouble Codes (DTCs) B0434 and/or B3764 have been set.

These conditions may be caused by HVAC actuators that hunt for the correct position. This cycling may cause a clicking or ticking noise.

An overtravel of the HVAC system control doors may cause one or more of the above system conditions. If an overtravel occurs, a DTC will be set, and the door will go to a preset default position.

When a system door defaults, that door will stay at the default position until the DTC is cleared. Clearing the DTC will allow the door to operate properly until the overtravel condition reoccurs. The following table lists the DTCs that may have been set and the door that is associated with that code.

Technicians are to replace the auxiliary (rear) HVAC control module with the part number listed in the table below. Refer to the Auxiliary Heater and Air Conditioning Control Module Replacement procedure in SI for more information. This module contains a new calibration to compensate for the actuator overtravel condition and the hunting/clicking noises. The new calibration effectively eliminates DTCs B0434 and B3764. The new control module also eliminates the default position of the doors associated with the DTC. The new control module will allow door travel from counts 0 to 255 without setting a DTC or defaulting the door.

The new auxiliary HVAC control module is compatible with either the first or second design blower motor control module. When using the new auxiliary HVAC control module, the customer may notice a slight increase in the rear blower motor speed (approximately 50 rpm) at a given setting, as compared to the blower motor speed at the same setting with the original HVAC control module. If the customer comments that the increase in blower speed at a given setting is objectionable, the blower motor control module may be replaced with the second design part listed below to correct the slight increase in speed.

The revised auxiliary HVAC control module should not be used unless one or both of the DTCs are set or one or more of the conditions listed above are present. The revised auxiliary HVAC control module will not correct any other DTC or Air Conditioning (A/C) performance concern.

The blower motor control modules listed below should not be used unless the customer finds the change in blower speeds between the original and the new auxiliary HVAC control modules objectionable.

For vehicles repaired under warranty, use: