TECH 1 RWAL/4WAL BRAKE CARTRIDGE DIAGNOSIS

Subject: TECH 1 - 1988-91 RWAL/4WAL BRAKE CARTRIDGE DIAGNOSIS

Model and Year: 1991 C/K, RN, G, M/L AND S/T TRUCKS

Recently, two (2) conditions were discovered with the 1988-91 TK02640A RWAL/4WAL BRAKE Tech 1 cartridge. Listed below are divisions affected, descriptions of the conditions, and the recommended corrective action.

DIVISIONS NOT AFFECTED:

Chevrolet dealers who are recipients of original 1988-90 RWAL/4WAL Essential Cartridge.

CONDITION #1 - INCORRECT 4WAL CODE 36 DESCRIPTOR DISPLAY -------------------------------------------------------- If the 4WAL code 36 has been set on the vehicle, the Tech 1 will display the CORRECT code number with an INCORRECT code descriptor. The RWAL/4WAL cartridge will currently display through the Tech 1 "CODE 36 MISSING LEFT FRONT SPEED SIGNAL". The correct descriptor should be "CODE 36 MISSING LEFT REAR SPEED SIGNAL".

RECOMMENDED ACTION:

It is recommended to follow the CODE 36 diagnostic chart in the vehicle service manual. Note that the service manual identifies the correct wheel signal. Since the tool displays the CORRECT code, following the chart WILL correctly diagnose the vehicle condition/symptom.

CONDITION #2 - RWAL INVALID CODE INDICATION -------------------------------------------- Recently a new RWAL ECU was released for 1991 production vehicles that has a changed ALDL Data Signal and is a service replacement part for 1988 and later model years. This ECU signal will cause the Tech 1 to display "INVALID CODE INDICATED" when communicating with the RWAL system and no codes are stored. The tool will display the correct code and function normally when a trouble code is set in the vehicle.

RECOMMENDED ACTION:

Use the original 1988-90 TK02640 RWAL/4WAL cartridge for servicing all RWAL equipped vehicles. The original cartridge will work correctly with all RWAL equipped vehicles.

REVISION EXCHANGE PROCEDURE:

All dealers who received the 1988-91 TK02640A RWAL/4WAL cartridge may exchange it for a revised TK02640A-Rl. This cartridge corrects conditions #1 and #2. This exchange will be in effect from May 1, 1991 through June 30, 1991. Following is the procedure for returning the 1988-91 Truck RWAL/4WAL TK02640A cartridge:

1.) Package your 1988-91 RWAL/4WAL cartridge in the smallest box possible. Only the affected cartridge should be returned. Accompanying cables, manual, and adaptors in the kit are not affected and should not be returned with the cartridge.

2.) Send the cartridge to the following address:

Service Technology Group 6483 Calle Real Goleta, CA 93117 ATTN: Mr. R. Davalos

3.) Make sure your return address is clearly marked on the outside of the carton and included with the cartridge on the inside of the carton.

The new cartridge will be shipped second day freight to each dealer after the original 1988-91 RWAL/4WAL TK02640A cartridge has been received at the above address. Any questions can be directed to the toll free customer support number: 1-800-828-6860. Press "2" for service, and then "2" again for Tech 1 product.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.