Engine Control Module: Description and Operation

Engine Control Module:

ENGINE CONTROL MODULE
The Engine Control Module (ECM) is the control center of the fuel injection system. It constantly looks at the information from various sensors, and controls the systems that affect vehicle performance.

SELF-DIAGNOSTICS
The ECM has the capability to diagnose faults in the sensors, input switches, components and systems they control. When the ECM recognizes a problem, it may turn "ON" the "Service Engine Soon" Malfunction Indicator Lamp (MIL) lamp "ON" to alert the driver that a malfunction has occurred. The MIL is located in the instrument cluster.

When a fault in the Computer Control System has been detected, the ECM will turn on the MIL to warn the driver of a problem. A Diagnostic Trouble Code (DTC) will be stored in the computer memory for retrieval by the technician. The DTC will be lost in memory after a certain number of engine starts or if power is removed from the ECM.


OPERATION
The computer 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.

LEARNING ABILITY
The computer has a learning ability which allows it to make corrections for minor variations in the fuel system to improve driveability. If the battery is disconnected to clear trouble codes or for repair, the learning process has to begin all over again, and a change may be noticed in the driving performance of the vehicle. To reset the vehicles learning ability, make sure the engine is at operating temperature and operate the vehicle at part throttle, moderate acceleration, and idle conditions, until normal performance returns.

COMPONENTS
Vehicles have an ECM with two serviceable parts. A controller called a ECM, without a Programmable Read Only Memory (PROM), and a PROM with specific programming information.

NOTE: When a production ECM is replaced with a service ECM, it is important to transfer the broadcast code and production number from the original ECM to the service ECM. This allows for positive identification of ECM parts throughout the service life of the vehicle. DO NOT affix the information to the ECM cover.