SOFT/SPONGY BRAKE PEDAL FEEL POSSIBLE CODE 4

MODELS: 1989 M-VAN AND S/T TRUCKS

Some 1989 M-Van and S/T Trucks were built with Isolation/Dump Valve Assemblies (see Figure No. 1) that may contain small metal particles. These metal particles may lodge themselves between the Dump Valve Check Ball and Ball Seat. If this occurs, a pressure differential will occur between the Isolation Valve and the Dump Valve, causing the instrument panel brake light to come on, and set a Code 4. This condition will not affect the normal braking of the vehicle. However, Rear Wheel Antilock will be deactivated (and dash brake light will so indicate that the system is not active) and brake pedal feel will be soft/spongy.

IMPORTANT: The small metal particles will remain trapped inside the Isolation/Dump Valve and will not migrate into the remainder of the hydraulic system.

To eliminate this condition, replacement of the Isolation/Dump Valve is required.

PARTS INFORMATION

IMPORTANT: No affected Isolation/Dump Valve Assemblies were ever shipped to GMSPO.

Parts are expected to be available on February 13, 1989. Until then, norrnal part orders will not be accepted by GMSPO. Only verifiable emergency VIP orders will be accepted. SPO will make every effort to obtain parts. All parts will be placed on 400 control to waive VIP surcharges. However, the part will be shipped premium transportation at dealer's expense. All other order types will be cancelled as incorrectly ordered wbile the 400 control is in place.

PART NUMBER DESCRIPTION MODEL ------ ----------- ----- 15618244 Isolation/Dump Valve S/T and M

For repair to vehicles under warranty, use:

Labor Op: H2480 Labor Time: S/T 1.0 Hr. M .9 Hr.

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.