Join Date: Mar 2005
Location: Tiny Pebble, AR
A feedback signal failure can occur on the blend
or mode door. The body control module monitors the
feedback signal to check the position of the actuator.
The body control module not only checks the level of
the signal but also how much the voltage changes.
A feedback failure can occur if there is a short or
open circuit in the wiring, a bad actuator, a bad
body control module, a bad HVAC unit door or
connecting linkage. The easiest way to diagnose
this is to use the DRB to actuate the blend or mode
door. Note that the feedback voltage of the actuator
should smoothly change as the actuator is moved. A
sudden change in the feedback voltage to a 5.0-volt
or a 0.0-volt level indicates the actuator is bad. A
fixed feedback voltage that is less than 5.0 volts or
greater than 0.0 volts without a stall failure, or a
short failure indicates that the actuator, the HVAC
unit door, or a connecting mechanical linkage is
jammed thereby preventing movement. A feedback
signal voltage that stays on 5.0 volts or 0.0 volts
indicates a wiring or body control module problem.
The feedback voltage should always be less than 5.0
volts and greater than 0.0 volts.
The feedback trouble code can also occur from
lack of actuator travel. This can be checked by
confirming that the feedback signal smoothly
changes when the actuator is moved with the DRB.
If the signal is OK, the door travel is not correct.
The actuator must be removed and the HVAC unit
door mechanically checked for proper operation.
Typical problems that prevent door movement in
clude screws dropped in the HVAC unit or warped
doors. Replace any part that is found defective.
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