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.

QDR Application Chart:

QDR Application Chart For CHART C-1

The following chart contains ECM QDR arrangement for all ECM models thru 1987.*
Important Note:

^ Many 82-83 ECMs did not use QDRs, and will not appear on the chart.

^ This procedure will not work on any ECM Service Number which does not appear on the chart. (This is because such an ECM does not contain QDRs.)

^ Not all available QDR outputs are used for ECM application. Verify circuit usage from the ECM wiring diagrams for each specific engine using Section "6E" of the service manual.

*Additional ECMs listed on page 4

ECM - CHECK CHART:

CHART C-1

ECM QDR CHECK

QDR APPLICATION CHART:

QDR Application Chart For CHART C-1

The following chart contains ECM QDR arrangement for all ECM models thru 1987.
Important Note:

^ Many 82-83 ECMs did not use QDRs, and will not appear on the chart.

^ This procedure will not work on any ECM Service Number which does not appear on the chart. (This is because such an ECM does not contain QDRs.)

^ Not all available QDR outputs are used for ECM application. Verify circuit usage from the ECM wiring diagrams for each specific engine using Section "6E" of the service manual.