GM Astro/Safari 1985-1996 Repair Guide

Electronic Control Module (ECM)



When the term Electronic Control Module (ECM) is used in this guide it will refer to the engine control computer regardless that it may be a Vehicle Control Module (VCM), Powertrain Control Module (PCM) or Engine Control Module (ECM).

The Electronic Control Module (ECM) is required to maintain the exhaust emissions at acceptable levels. The module is a small, solid state computer which receives signals from many sources and sensors; it uses these data to make judgments about operating conditions and then control output signals to the fuel and emission systems to match the current requirements.

Engines coupled to electronically controlled transmissions employ a Powertrain Control Module (PCM) or Vehicle Control Module (VCM) to oversee both engine and transmission operation. The integrated functions of engine and transmission control allow accurate gear selection and improved fuel economy.

In the event of an ECM failure, the system will default to a pre-programmed set of values. These are compromise values which allow the engine to operate, although at a reduced efficiency. This is variously known as the default, limp-in or back-up mode. Driveability is almost always affected when the ECM enters this mode.


See Figures 1 and 2

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Fig. Fig. 1: ECM mounting scheme-except 1996 models

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Fig. Fig. 2: ECM mounting scheme-1996 models

The ECM is located in the passenger side footwell in the kick panel up to 1996. In 1996, the ECM is located in the engine compartment next to the battery.

  1. Disconnect the negative battery cable.
  3. Disengage the connectors from the ECM.
  5. Remove the spring retainer off and over the rail of the ECM on vehicles except 1996.
  7. Slide the ECM out of the bracket at an angle.
  9. Remove the ECM.

To install:
  1. Install the ECM into the bracket.
  3. Install the spring retainer (except 1996) and plug in the electrical connectors.
  5. Connect the negative battery cable.