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Engine Control Module Description

The engine control module (ECM) interacts with many emission related components and systems, and monitors the emission related components and systems for deterioration. OBD II diagnostics monitor the system performance and a diagnostic trouble code (DTC) sets if the system performance degrades.

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. Type C is a non-emissions-related DTC.

The ECM is located in the engine compartment. The ECM is the control centre of the engine controls system. The ECM controls the following components:

The ECM constantly monitors 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 recognise operational conditions and alert the driver via the MIL. When the ECM detects a malfunction, the ECM stores a DTC. The condition area is identified by the particular DTC that is set. This helps the technician in making repairs.

The engine control module (ECM) can supply 5 V or 12 V to the various sensors or switches. This is done through pull-up resistors to the regulated power supplies within the ECM. In some cases, even an ordinary shop voltmeter will not give an accurate reading because the resistance is too low. Therefore, a DMM with at least 10 MΩ input impedance is required in order to ensure accurate voltage readings.

The ECM controls the output circuits by controlling the ground or the power feed circuit through the transistors or a device called an output driver module.

The programmable read only memory (EEPROM), which can be erased electronically, is a permanent memory that is physically part of the engine control module (ECM). The EEPROM contains program and calibration information that the ECM needs in order to control the powertrain operation.

Special equipment, as well as the correct program and calibration for the vehicle, are required in order to reprogram the ECM.

When a malfunction occurs within the engine control system, the engine control module (ECM) maintains control of the system with default actions. Default actions are calculated values, and/or calibrated default values, that are stored within the ECM. A certain level of engine performance is possible when a malfunction occurs dependant on the default actions taken. The ECM default actions prevent a complete loss of engine performance.

The scan tool can control certain solenoids, valves, motors, and relays. The output controls can be found under the Special Functions selection of the scan tool. Some output controls may be disabled by the engine control module (ECM) during certain types of vehicle operation.

The data link connector (DLC) is a 16-pin connector that provides the technician with a means of accessing serial data for aid in the diagnosis. This connector allows the technician to use a scan tool in order to monitor the various serial data parameters, and display the DTC information. The DLC is located inside the drivers compartment, underneath the dash.

The malfunction indicator lamp (MIL) is located on the instrument panel cluster or the driver information centre. The MIL is controlled by the engine control module (ECM) and illuminates when the ECM detects a condition that affects the vehicle emissions.

The engine control module (ECM), by design, can withstand the normal current draws that are associated with the vehicle operations. However, care must be taken in order to avoid overloading any of these circuits. When testing for opens or shorts, do not ground or apply voltage to any of the ECM circuits unless the diagnostic procedure instructs you to do so. These circuits should only be tested with a DMM.

Note:  Do not attach add-on vacuum operated equipment to this vehicle. The use of add-on vacuum equipment may result in damage to vehicle components or systems.

Note: Connect any add-on electrically operated equipment to the vehicle's electrical system at the battery (power and ground) in order to prevent damage to the vehicle.

Aftermarket, add-on, electrical and vacuum equipment is defined as any equipment installed on a vehicle after leaving the factory that connects to the vehicles electrical or vacuum systems. No allowances have been made in the vehicle design for this type of equipment.

Add-on electrical equipment, even when installed to these strict guidelines, may still cause the powertrain system to malfunction. This may also include equipment not connected to the vehicle electrical system, such as portable telephones and radios. Therefore, the first step in diagnosing any powertrain condition is to make sure all of the after-market electrical equipment is removed or disconnected from the vehicle. After this has been done and if the condition still exists, the condition may be diagnosed in the normal manner.

Note: In order to prevent possible electrostatic discharge damage to the ECM, do not touch the connector pins on the ECM.

The electronic components that are used in the control systems are often designed to carry very low voltage. The electronic components are susceptible to damage caused by electrostatic discharge. Less than 100 V of static electricity can cause damage to some electronic components. By comparison, it takes as much as 4000 V for a person to even feel the zap of a static discharge.

There are several ways for a person to become statically charged. The most common methods of charging are by friction and by induction. An example of charging by friction is a person sliding across a car seat.

Charging by induction occurs when a person with well insulated shoes stands near a highly charged object and momentarily touches ground. Charges of the same polarity are drained off leaving the person highly charged with the opposite polarity. Static charges can cause damage, therefore, it is important to exercise great care when handling and testing electronic components.

Note: This inspection is very important and must be done carefully and thoroughly.

Perform a careful underbonnet inspection when performing any diagnostic procedure or diagnosing the cause of an emission test failure. This can often lead to repairing a condition without further steps. Use the following guidelines when performing an inspection: