See Figure 1
Whenever the term Electronic Control Module (ECM) is used in this guide, it will refer to the engine control computer, whether it is a Powertrain Control Module (PCM) or Electronic Control Module (ECM).
The heart of the electronic control system, which is found on the vehicles covered by this guide, is a computer control module. The module gathers information from various sensors, then controls fuel supply and engine emission systems. Most early model vehicles are equipped with an Engine Control Module (ECM) which, as its name implies, controls the engine and related emissions systems. Later model vehicles may be equipped with a Powertrain Control Module (PCM). This is similar to the original ECMs, but is designed to control additional systems as well. The PCM may control the manual transaxle shift lamp or the shift functions of the electronically controlled automatic transaxle.
Regardless of the name, all computer control modules are serviced in a similar manner. Care must be taken when handling these expensive components in order to protect them from damage. Carefully follow all instructions included with the replacement part. Avoid touching pins or connectors to prevent damage from static electricity.
All of these computer control modules contain a Programmable Read Only Memory (PROM) chips that contains calibration information specific to the vehicle application.
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.
REMOVAL & INSTALLATION
See Figure 2