File in Section:

Service Bulletin

Bulletin No.:
Date:

PIT5322
September, 2014

PRELIMINARY INFORMATION
Subject:

PIT5322

Models:

2015 Chevrolet Colorado
2015 GMC Canyon

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern
The HVAC blower motor used on these models has a normal delay when being turned ON to any blower speed from
the OFF position. When the blower motor control is moved from the OFF position to any blower speed, there is an
approximate 5 second delay before the blower motor begins to increase to the selected speed setting. This blower
motor is a brushless design and operates differently than past models in that it uses back electromagnetic field
(EMF) to control operation.
An electromagnetic field (EMF) is a physical field produced by electrically charged objects. It affects the behavior of
charged objects in the vicinity of the field. The HVAC blower motor used on these vehicles has an approximate 5
second delay on start up after manually adjusting the power knob from OFF to ON. The biggest contributor to the
delay in the start time is in the motor start-up phase, where the EMF is used to synchronize the rotor, which takes
approximately 3 seconds all by itself. The back EMF method requires that current flows through the motor windings
at a sufficient level in order to function without error. During this phase, the motor performs some critical functions
while spinning the rotor up from 20 RPM to 450 RPM, in order to get a sufficient current generated, which allows the
rotor position to be synchronized with the magnetic field rotation. Once this occurs the motor starts its ramp up

Recommendation/Instructions
This is a normal operating characteristic. No repairs or part replacements should be performed for this characteristic
operation.

Customer Information
Please communicate to the customer this condition is a normal operating characteristic of their vehicle. It will not
impact the designed performance or reliability of the vehicle. Please share this information with the customer,
including a copy of this message.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is
resolved without completing every step, the remaining steps do not need to be performed.