Engine Control Module: Description and Operation

The ECM is a multifunction electronic controller that monitors engine and vehicle operating conditions, calculates ideal EGR and converter clutch operation, and controls EGR and TCC operation based on these calculations. In addition, the ECM provides diagnostic logic which detects faults in the systems that it monitors or controls.
The ECM monitors engine RPM, vehicle speed, EGR operating vacuum and injector pump metering valve (throttle) position in order to control EGR and TCC operation. The ECM controls operation of these two systems by energizing or de-energizing control solenoids, which in turn control operating vacuum to the EGR and EPR valves and engagement of the torque converter clutch.
If a malfunction is detected within the system, the ECM illuminates a ``Check Engine'' lamp on the instrument panel. However, the ECM does not store malfunctions as trouble codes, as in other type systems, nor does it flash the lamp to indicate the nature of the malfunction. Instead, the type malfunction can be determined by observing operation of the lamp. A malfunction detected in the vacuum system will cause the lamp to come on and remain on until the ignition is switched off, while electrical malfunctions will cause the lamp to illuminate only under the operating conditions when the malfunction occurs.