K 2500 Truck 4WD V8-379 6.2L DSL (1989)
Antilock Brake Module: All Technical Service Bulletins
Brakes - ECU Software Improvement
Number:
91-101-5
Section:
5
Date:
November 1990
Corp. Bulletin No.: 065021
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 10 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.
