K 2500 Truck 4WD V8-379 6.2L DSL VIN C FI (1989)
Fan Clutch: Technical Service Bulletins
A/T - Intermittent Downshift/Slip/Cycling Diagnosis
File In Section: 07 Transmission/Transaxle
Bulletin No.: 99-07-30-016B
Date: October, 2002
INFORMATION
Subject:
Diagnostic Information For Intermittent Transmission Downshift, Slip, Busy/cycling TCC or Noisy Cooling Fan
Models:
1999-2000 Cadillac Escalade
2002-2003 Cadillac Escalade, Escalade EXT
1988-2003 Chevrolet Astro, Blazer, S-10, Silverado, Suburban
1989-2003 Chevrolet/Geo Tracker
1995-2003 Chevrolet Tahoe
1996-2003 Chevrolet Express
1988-1994 GMC S-15
1988-1999 GMC Suburban
1988-2003 GMC Safari, Sierra
1995-2003 GMC Sonoma, Yukon, Yukon XL
1996-2003 GMC Savana
1999-2001 GMC Envoy
1991-2001 Oldsmobile Bravada
2003 HUMMER H2
with Air Conditioning
This bulletin is being revised to change the Model information and text. Please discard Corporate Bulletin Number 99-07-30-016A (Section 07 -
Transmission/Transaxle)
Some customers may comment that at times the transmission seems to slip, or that there is a loud roar from the engine with slow acceleration. This
condition is most noticeable after the vehicle has sat idle for 12 or more hours, or on hot days when the A/C is on and the vehicle moves slowly with
traffic.
Typical comments from customers may include the following conditions:
^
Intermittent slipping
^
Intermittent downshift followed by an upshift, both with no apparent reason
^
Busyness or cycling of the TCC (torque converter clutch) at steady throttle conditions and on a level roadway
^
Noisy cooling fan
The type of concern described above requires further definition. The customer should be asked the following questions:
^
Is the situation more pronounced with higher vehicle loads such as when pulling a trailer?
^
Do warmer ambient temperatures make the situation more pronounced?
^
When the condition occurred, did you have the A/C on, and were you driving in stop and go city traffic?
^
Does the condition exhibit itself on the first start-up after sitting more than eight hours?
If the customer indicates that these conditions apply, and your observation confirms that the vehicle is operating properly, provide the customer with the
vehicle operating description included at the end of this bulletin. Further action may not be necessary. A service procedure follows if further definition is
required.
Diagnostic Aids
Cooling fan operation or the resulting sound varies. The cooling fan clutch may be described as a continuously variable clutch. If the vehicle engine is
running, the fan blade is always turning unless the fan clutch is non-functional. The speed of the fan in relation to engine speed is temperature dependent.
