RWAL BRAKE CODES 6,9,10 AS SOFT CODES-SERV INFO

Subject: INTRODUCTION OF CODES 6, 9 AND 10 AS SOFT CODES

Model and Year: 1988-91 C/K, S/T, R/V, G AND M TRUCKS WITH RWAL

TO: ALL CHEVROLET DEALERS

Beginning in August 1990, a software change was made to the Electronic Control Units on all RWAL equipped vehicles. This software improvement will change codes 6, 9, and 10 to "Soft Codes." The conditions which set these codes remain the same, as well as the diagnostics technicians should follow to determine the root cause.

Codes 6 and 9 will light the brake light when a fault is detected and the applicable code will be stored in memory. The brake light will remain on until the next ignition cycle at which time if the fault is not present, the brake light will remain off. The code, will still remain in memory as a "Soft Code." If the code should reoccur, the brake light will again be illuminated for the duration of that ignition cycle.

A code 1 0 will set if the brake pedal is depressed or the brake switch circuit is opened and remains open until vehicle speed passes approximately 38 MPH. This soft code differs from codes 6 and 9 in that the red brake light will be illuminated only while the fault is detected. Code 10 will remain stored in the ECU memory after the light has been turned off.

IMPORTANT: Technicians MUST use a Tech One scan tool to read codes. This is because soft codes will be erased by grounding terminals A to H and a false code 9 could be set if this is attempted.

The new ECUs can be identified by the code printed on the bottom of the longer of two bar code labels on the module. Older ECUs will have a fifteen digit alphanumeric code beginning with 912349K. New ECUs with the soft code software will have a code that begins with 919220K.

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.