ABS - 4WAL Deactivated, Code 66 (Pump Motor Relay) Set

90chevy15
GMC NUMBER: 90-5E-62

GROUP: 5E Anti-Lock

DATE: May, 1990

CORPORATE
NUMBER: 065005
SUBJECT: CODE 66 (PUMP MOTOR RELAY SHORTED)

MODELS: 1990 M/L VANS WITH 4 WHEEL ANTI-LOCK 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 15005.05-1 RWAL UPDATE 4WAL PREVIEW which was mailed under GMC cover bulletin 90-5E-07 (October 1989).

SERVICE PARTS INFORMATION Current service part numbers have not changed, however all GMSPO 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

Parts are currently available through GMSPO.

WARRANTY INFORMATION For vehicles repaired under warranty use:
LaW Operation: H2505
Labor Time: 1.6 hrs.