CODE 66/PUMP MOTOR RELAY SHORT SERVICE PARTS AND PROCEDURE

SUBJECT: CODE 66/PUMP MOTOR RELAY SHORTED (SERVICE PARTS AND PROCEDURE)

VEHICLES AFFECTED: 1990 M AND L VANS WITH 4WAL BRAKES

Some 1990 M/L Vans built prior to the VIN breakpoints listed below may experience a condition which will cause a code 66 to be set and deactivate the anti-lock feature of the 4WAL system. This condition is most likely to occur when the vehicle is shutoff with the blower motor on and the brake pedal depressed.

In this situation normal blower motor "coast-down" may cause the 4WAL pump motor to momentarily turn on. The resulting inrush of current from the pump can create arcing of the internal relay contacts as they open and this could result in the relay contacts being stuck shut and a code 66 being set. This code will also deactivate the anti-lock feature of the 4WAL system.

To correct this condition the EHCU module has been revised to prevent electrical feedback from the blower motor activating the pump.

Vehicles built after the following VIN breakpoints have the revised EHCU module installed.

Chevrolet LB168081 GMC Truck LB522580

DIAGNOSTIC INFORMATION:

Technicians should follow Code 66 diagnostic information given in manual 155005.05-1 RWAL UPDATE 4WAL PREVIEW.

SERVICE PARTS INFORMATION:

Current service part numbers have not changed, however, all CANSPO stock has been purged of the past design EHCU.

PART NUMBER DESCRIPTION MODEL

15649174 EHCU module 1990 M Van 15649175 EHCU module 1990 L Van

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.