REAR WHEEL ANTI-LOCK BRAKES - CODE 5 STORED

MODELS: 1988 K MODELS

On some 1988 K model trucks, the wiring harness which goes to the front axle switch (circuit #420 - Figure No. 1) may not have been connected at the assembly plant. If the vehicle is driven in four wheel drive with the harness disconnected, a code 5 will be stored in the rear wheel antilock (RWAL) brakes's electronic control unit (ECU). This will cause the electronic control unit to disable the antilock brakes allowing the vehicle to operate with conventional brakes only.

Trouble codes are read by jumping terminal A of the ALDL to terminal H of the ALDL and observing the flashing of the brake warning light. The terminals must be jumped for about 20 seconds before the code will begin to flash. In counting code pulses, count the number of short flashes, starting from the long flash. Include the long flash as a count. SOMETIMES THE FIRST COUNT SEQUENCE WILL BE SHORT, HOWEVER, SUBSEQUENT COUNTS WILL BE ACCURATE. If there is more than one failure, only the first recognized failure code will be retained and flashed.

If any code other than 5 is stored, follow the diagnosfic charts provided in the 1988 Light Duty C/K Service Manual, Section 5A3. On K models with a code 5 stored, follow the attached diagnostic chart.

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.