General System Description
Engine Control Module:
Description
The Engine Control Module (ECM) uses sensors and other inputs in order to obtain the information about the engine/vehicle operation and on the various systems that it controls. The details of the basic operation are covered in Descriptions and Operations. The functional checks, the diagnosis, and the on-vehicle service are covered in Computer and Control Systems.
On-Board Diagnostics
This vehicle is equipped with advanced diagnostic capabilities. The OBD II system is a much more complex system than the prior on-board diagnostics. The ECM interacts with many more emission related components/systems and monitors emission related components/systems for deterioration. Most of these diagnostics will detect a problem before the customer notices a change in the driveability. Rather than waiting for a hard circuit/component failure, OBD II diagnostics monitor the system performance, and a Diagnostic Trouble Code (DTC) will set if the system performance degrades.
Powertrain Diagnostic Trouble Codes
The Malfunction Indicator Lamp (MIL) operation and the DTC storage are dictated by the DTC type. A DTC is ranked as a Type A or Type B if the DTC is emissions related. Types C and D are not emissions related. Each DTC type has its own set of MIL operation, a DTC storage and a DTC clearing criteria.
Operation
The ECM is in the engine compartment, inside the relay center. The ECM is the control center of the engine controls system. The ECM controls the following components:
^ The fuel Injection system
^ The ignition system
^ The Emission Control systems
^ The On-board diagnostics for engine functions
^ The A/C and Multi-Ram systems
The ECM constantly looks at the information from various sensors and other inputs, and controls the systems that affect the vehicle performance and the emissions. The ECM also performs diagnostic tests on various parts of the system. The ECM can recognize operational problems and alert the driver via the Malfunction Indicator Lamp (MIL). When the ECM detects a malfunction, the ECM stores a Diagnostic Trouble Code (DTC). The problem area is identified by the particular DTC that is set. This aids the technician in making repairs.
The ECM connects to the engine wiring harness by one 88-pin connector.
ECM Function
The ECM can supply 5 volts or 12 volts to the various sensors or switches. This is done through pull-up resistors to the regulated power supplies within the ECM. The resistance is so high in value that a test light will not light when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading because the resistance is too low. Therefore, a digital voltmeter (J 39200) with at least 10 megohms input impedance is required in order to ensure accurate voltage readings.
The ECM controls the output circuits such as the injectors, the relays, the IAC, etc. by controlling the ground or the power feed circuit through the transistors or a device called an Output Driver Module.
ECM Learning Ability
The ECM has a learning ability which allows for making corrections for minor variations in the fuel system in order to improve the driveability. If the battery cable is disconnected, the learning process resets. A change may be noted in the vehicle's performance. To teach the vehicle, ensure that the engine is at the normal operating temperature, then turn ON the ignition key.
Idle Learn
Another method to teach the vehicle to idle is to drive the vehicle at part throttle, with moderate acceleration. You may also operate the vehicle at idle conditions until the normal performance returns.