Envoy 2WD V8-5.3L VIN P (2004)
Fan Clutch: Customer Interest
Engine Controls - Underhood Ticking Noise
Bulletin No.: 05-06-02-004
Date: April 06, 2005
TECHNICAL
Subject:
Underhood Tick Noise at Idle (Reprogram PCM)
Models:
2004 Buick Rainier
2002-2004 Chevrolet TrailBlazer Models
2002-2004 GMC Envoy Models
2002-2004 Oldsmobile Bravada
Condition
Some customers may comment on an underhood tick noise heard while the vehicle is idling. Technicians may find that the noise does not increase or
decrease with changes in the engine idle RPM. The tick noise occurs at approximately one second intervals.
Cause
This condition may be caused by the electro-viscous fan clutch control function of the Powertrain Control Module (PCM) attempting to keep the fan
speed between 300-600 revolutions per minute (RPM). At idle, the cooling fan speed will drag to approximately 500 RPM then oscillate between 300
and 600 RPM. When the fan speed drops below 500 RPM, the PCM will pulse the fan control solenoid. The pulsing of the solenoid is the cause of the
ticking noise.
Correction
Technicians are to verify that the cooling fan clutch is the source of the noise by using either one of the following two methods:
^
Use a Tech 2(R) to command the cooling fan off. If the ticking noise goes away, the pulsing of the cooling fan clutch is the source of the noise.
^
The cooling fan clutch electrical connector, located on the cooling fan shroud, may be disconnected with the engine off. If the ticking noise goes
away, the pulsing of the cooling fan clutch is the source of the noise. Be sure to clear any Diagnostic Trouble Codes (DTCs) that may have set while
the cooling fan clutch is disconnected.
Technicians are to reprogram the PCM with an updated software calibration. The new software calibration is currently available in TIS for all the
vehicles listed above.
Warranty Information
