The term Electronic Control Module (ECM) is used in this guide to refer to the engine control computer, whether it is a Powertrain Control Module (PCM) or an Engine Control Module (ECM).
The heart of the electronic engine management system, which is found on the vehicles covered by this guide, is the ECM/PCM control module. On vehicles equipped with a manual transaxle, there is no need for a control unit to control shift points as the transaxle is shifted manually. On these models, the engine management system uses an ECM. Some models used a separate Transmission Control Module (TCM) that is linked with the ECM to control the automatic transaxle shift points.
Many models equipped with an automatic transaxle, the Transmission Control Module (TCM) and Engine Control Module (ECM) have been combined into one unit, called the Powertrain Control Module (PCM). The ECM/PCM processes input information from various sensors, compares the input with pre-programmed information and sends output signals to control the fuel supply, ignition timing, and the engine emission system. The PCM also controls the shift functions of the on vehicles equipped with an automatic transaxle.
Regardless of who the manufacturer may be, all computer control modules are serviced in a similar manner. Care must be taken when handling these expensive electronic 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 or contaminating the electrical connection. Some input voltages and resistance values are quite small and the readings very sensitive. A poor electrical connection could drastically affect the values recognized by the PCM and cause a poor running condition.
Since the PCM is a sensitive electronic component and must be kept away from areas of heat, debris and fluids, it is located in the interior.
All of the computer control modules contain a Programmable Read Only Memory (PROM) chip that contains calibration information specific to the vehicle application.
In case 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 or back-up mode. Drivability is usually affected when the ECM enters this mode and should trigger the Malfunction Indicator Lamp (MIL) indicator.
The ECM can be reset by removing the BACK UP (7.5 A) fuse for 10 seconds.
Removing the BACK UP (7.5 A) fuse cancels the clock and radio presets.
REMOVAL & INSTALLATION
Sometimes substituting a known good ECM/PCM can be helpful when attempting to diagnose a problem in the engine management system. When substituting a control unit, make sure that both control units are identical. Installing the wrong control unit could damage the substituted unit, and/or possibly damage other related sensors or components in the vehicle being tested.
The control units are very sensitive to changes in the charging system operating voltage and voltage spikes. Make sure the alternator and battery are functioning properly. An alternator that is over charging will not only damages the battery, the voltage output may be enough to cause damage to other electrical components and control units.
Operating a vehicle with a discharged or defective battery can cause the vehicle's charging system to be overworked. Never operate a vehicle with a battery cable disconnected. If the vehicle requires a jump start, be careful to connect the battery cables properly, and wait at least one minute after the cables have been installed the start the vehicle.
Always ground yourself when handling an ECM. This can easily be done by connecting a small jumper lead to you and then to the metal chassis of the vehicle.
- Pull back the carpeting from the passengers floor and front console. This will expose the ECM.
- Remove the two (2) bolts on four-cylinder models or the three (3) bolts on six-cylinder models.
- Remove the wiring harnesses from the ECM.
- Lift the ECM from the vehicle.
Remember to properly ground yourself when handling the ECM. It only takes a small spark of static electricity to destroy the fragile electronics within the ECM.
- Installation is the reverse of removal.