Recall - High/Low/High ABS Brake Anomaly: Overview
File in Section: Special PricesBulletin No.: 99046
Date: December, 1999
SPECIAL POLICY
SUBJECT:
99046 - SPECIAL POLICY - HIGH/LOW/HIGH ABS BRAKE ANOMALY
MODELS:
1993-1996 CHEVROLET, GMC, AND OLDSMOBILE S/T UTILITY
1994-1996 CHEVROLET AND GMC S/T PICKUP EQUIPPED WITH A V6 ENGINE
1993-1995 CHEVROLET AND GMC M/L VAN
1993-1996 CHEVROLET AND GMC G VAN
THIS SPECIAL POLICY IS IN EFFECT UNTIL DECEMBER 1, 2002
DUE TO THE AVAILABILITY OF PARTS, THIS SPECIAL POLICY WILL BE ADMINISTERED IN PHASES. THIS FIRST PHASE WILL BE THE REPROGRAMMING OF THE VCM IN 2WD AND 4WD 1994-1996 S/T PICKUPS AND 1995-1996 S/T UTILITIES EQUIPPED WITH A VCM. VEHICLES INVOLVED IN PHASE 1 ARE SHADED IN THE TABLE.
YOU WILL BE NOTIFIED OF THE NEXT PHASE VIA DCS MESSAGE.
Condition
The federal government's highway safety agency, the National Highway Traffic Safety Administration (NHTSA) has identified, and General Motors Corporation has confirmed, the existence of a condition in the antilock braking system of some Chevrolet, GMC, and Oldsmobile S/T utilities. 1994-1996 Chevrolet and GMC S/T pickups equipped with a V6 engine, 1993-1995 Chevrolet and GMC M/L vans, and 1993-1996 Chevrolet and GMC G vans, all equipped with the Lucas Varity three-sensor ABS system. On rare occasions, this condition can result in longer stopping distances during certain antilock brake applications, as explained below.
If the customer is driving on a road surface that supports good traction and they begin to stop by applying the brake pedal firmly, and both front wheels of their vehicle then pass onto a slippery surface (such as an ice-covered or wet patched asphalt part of the road), the antilock brake system will adjust the brakes at each of the wheels to take advantage of the available traction. This will allow the customer to steer and maintain stability, which is normal ABS operation1 as their owner's manual explains in more detail.
However, if the customer is still braking while the vehicle leaves the slippery surface and both front wheels get back on a higher-traction surface, the ABS may perform as if the vehicle were still on the slippery surface and the vehicle may not stop as quickly. However, this will not happen every time these conditions are encountered. It depends on several additional factors, such as vehicle speed and the length of the slippery surface.
The ABS system was designed with increased sensitivity to wheel slip in order to improve vehicle steerability while braking on very slippery surfaces. This improvement for steerability, however, made it possible for reduced front braking effectiveness to occur as described above.
SPECIAL POLICY ADJUSTMENT (Phase I)
This special policy adjustment covers the condition described above- until December 1, 2002, regardless of vehicle mileage or ownership. Dealers are to reprogram the VCM. Use the following Service Procedure. This will be performed at no charge to the customer during this time. Other conditions that may cause similar or different brake complaints that are not a result of the condition listed above are not covered by this special policy. The customer should be informed that any further service that is not covered by this special policy would be their responsibility, if they elect to have the service performed.
VEHICLES INVOLVED
Involved are 1993-1998 S/T utilities, 1994-1996 S/T pickups equipped with a V6 engine, 1993-1995 M/L van, and 1993-1996 G vans built within the VIN breakpoints.
PARTS INFORMATION
This phase requires no parts. Calibrations are available in October, 1999 on TIS 2000 CD, # 21 or Techline CD # 20/21 or later versions.
CUSTOMER NOTIFICATION
Customers will be notified of this special policy on their vehicles, in phases, by General Motors (see copy of typical customer letter included with this bulletin - actual divisional letter may vary slightly).
SERVICE PROCEDURE
VCM Programming
Important:
For 1995 S/T utilities with L35, check the Service Parts Identification (SPID) label on the inside of the glovebox to determine if the vehicle has a VCM. If there is an RPO of "K29", the vehicle has a PCM and is programmable.
The new calibration,will be available in October, 1999 on TIS 2000 CD # 21 or Techline CD # 20/21 and later versions. The calibration is programmed into the vehicle's VCM via a Techline TOOL. Use a Techline Terminal or scan tool to perform the learn procedure and program the VCM.
Important:
Use the calibration file "Special Policy 99046" on TIS 2000 CD # 21 or Techline CD # 20/21 or later versions.
1. To ensure VCM programming/RPO configuration, confirm that the following conditions exist in order to prepare for VCM programming:
^ The battery is fully charged
^ The ignition switch is in the "RUN" position
^ The Data Link Connector (DLC) is accessible
2. Refer to the latest Techline Terminal and equipment user's instructions.
3. Clear the diagnostic trouble codes (DTCs) after the programming is complete.
CLAIM INFORMATION
For vehicles repaired under warranty submit a claim with the information indicated.