Engine Control Module: Description and Operation

Engine Control Module:

Fig. 5 ECM Unit (Showing PROM & CALPAK Locations):

PURPOSE
The Engine Control Module (ECM) is the control center of the fuel injection system. It constantly looks at the information from various sensors (inputs) and controls the systems (outputs) that affect vehicle performance. The ECM also performs the diagnostic function of the system. It can recognize operational problems, alert the driver through the Malfunction Indicator Lamp (MIL) "Service Engine Soon" light on the instrument panel and store a Diagnostic Trouble Code(s) (DTC) in the ECM memory. The DTC identifies the problem areas to aid the technician in performing repairs.

OPERATION
The ECM is an electronic computer designed to process the various input information, and send the necessary electrical response to control fuel delivery, spark control, and other emission control systems. The ECM can control these devices through the use of Quad Driver Modules (QDM). When the ECM is commanding a device or a component "ON," the voltage potential of the output is "LOW" or near zero volts. When the ECM is commanding a device or component "OFF," the voltage potential of the circuit will be "HIGH," or near 12 volts. The primary function of the QDM is to supply the ground for the component being controlled.

The input information has an interrelation between sensor output. If one of the input devices failed, such as the oxygen sensor, this could affect more than one of the systems controlled by the computer.

The ECM has two parts for service:
- Controller which is the ECM, without the PROM, but with CAL-PAK
- PROM (Programmable Read Only Memory) which is a separate memory calibrator unit