S10/T10 P/U 2WD L4-119 1.9L VIN A 2-BBL (1984)
Engine Control Module: Technical Service Bulletins
ECM - Revised Replacement Procedure
Number:
87-150
Section:
6E
Date:
MAY, 1987
Subject:
REVISED ECM REPLACEMENT PROCEDURE - CHART C-1
Model and Year:
1982 THROUGH 1987 ECM EQUIPPED VEHICLES
TO:
ALL CHEVROLET DEALERS
The purpose of this bulletin is to introduce new ECM test procedures to reduce the possibility of multiple ECM failures on any one vehicle.
Since 1982, most ECM's have used an integrated circuit (IC) in place of separate transistors to turn "on" or "off" different components controlled by the
ECM. These IC's are called quad drivers (QDR). Each QDR has four separate outputs, meaning it can turn "on" or "off" four different items
independently.
A failed QDR usually results in an ECM output becoming either shorted to ground or open. Many times all four QDR output will be inoperative if just
one vehicle circuit is faulty.
The revised diagnosis incorporates new test procedures designed to identify a damaged QDR. Once identified, the circuit must be repaired to reduce the
incidence of repeat ECM failures.
This chart replaces the current service manual procedure for either:
1.
Chart C-1 ECM replacement check, or
2.
Any diagnostic chart where "replace ECM" is the conclusion, especially if a footnote indicates checking certain circuits for less than 20
OHM's resistance.
It is strongly suggested that this chart be used whenever an ECM replacement is indicated for 1982 through 1987 vehicles.