Underhood Tick Noise at Idle (Reprogram PCM)
| 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
DO THIS | DON'T DO THIS |
|---|---|
Reprogram the PCM. | DON'T Replace the engine cooling fan clutch. |
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® 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
For vehicles repaired under warranty, use:
Labor Operation | Description | Labor Time |
|---|---|---|
J6354 | Engine Control Module-Reprogram | Use Published Labor Operation Time |
Add | Diagnostic Time | 0.0-0.3 hr |
