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 this section.

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.

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 it's own set of MIL operation, a DTC storage and a DTC clearing criteria.

The Engine Control Module (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 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.

The Engine in this vehicle is a 3.0L dual overhead cam engine. The engine is a 54 cast iron block V6 with aluminum cylinder heads having 4 valves per cylinder. The engine is equipped with OBD II compliant electronic engine controls which reduce the exhaust emissions while maintaining excellent performance and fuel economy. The system also has advanced diagnostic capabilities.

The Engine Control Module (ECM) will be referred to as a control module. The control module is designed to maintain exhaust emission levels to Federal or California standards, while providing excellent driveability and fuel efficiency. Review the component sections and the wiring diagrams in order to determine which systems are controlled by each specific control module. The control module monitors numerous engine and vehicle functions and controls the following operations:

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.

The Electronically Erasable Programmable Read Only Memory (EEPROM) is a permanent memory that is physically part of the ECM. The EEPROM is not a removable component. The EEPROM contains program and calibration information that the ECM needs in order to control the powertrain operation.

Unlike the PROM used in the past applications, the EEPROM is not replaceable. If the ECM is replaced, make sure that the new ECM's software/calibration is correct for the vehicle and is the most recent version. Special equipment, as well as the correct program and calibration for the vehicle, is required in order to re-program the ECM.

This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). If the ECM is replaced, Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle. Refer to Electrical Diagnosis in Engine Electrical, Theft Deterrent System for the proper procedure. The vehicle will not start until this procedure is done.

The ECM employs an internal IC in order to continuously monitor the knock control evaluation circuit. The KS module IC contains the circuitry that allows the ECM to utilize the KS signals and diagnose the KS sensors and circuitry. The KS Module is not a replaceable component. If the ECM detects a fault in the ability of the IC to sample these signals, a DTC will set.

The DLC is a 16-pin connector that provides the technician 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 Diagnostic Trouble Code (DTC) information. The DLC is located inside of the driver's compartment, underneath the dash. Pin-4 and Pin-5 are grounds. Pin-7 is the ISO Serial Data. Pin-16 is B+

The Catera uses ISO serial data and communicates with the scan tool on DLC pin-7. Most other GM OBD II vehicles use Class 2 serial data on DLC pin-2. Both the ECM and the TCM communicate with the scan tool by using the ISO serial data circuit.

The Malfunction Indicator Lamp (MIL) is inside of the Instrument Panel Cluster (IPC). The MIL is controlled by the ECM illuminates when the ECM has detected a problem that affects the vehicle emissions.

The ECM, by design, can withstand the normal current draws that are associated with the vehicle operations. However, care must be used 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 Digital Voltmeter (J 39200 ).

Whenever you perform a ECM removal and replacement, follow the procedures in this section.

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 the 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, the OBD II diagnostics monitor system performance, and a Diagnostic Trouble Code (DTC) will set if the system performance is degraded.

The Malfunction Indicator Lamp (MIL) operation and the DTC storage are dictated by a DTC type. A DTC is ranked as a Type A or B if the DTC is emissions related. Types C and D are not emissions related. Each DTC type has an individual set of MIL operation, DTC storage and DTC clearing criteria.

This OBD II equipped vehicle is designed to self-diagnose any conditions that could lead to excessive levels of the following emissions:

Should this vehicle's onboard diagnostic system (ECM) detect a condition that could result in excessive emissions, the ECM turns on the MIL and stores a DTC that is associated with the condition. Always begin the diagnosis with the Powertrain OnBoard Diagnostic (OBD) System Check when diagnosing a condition reported from a state I/M program.

Additional information on the on-board diagnostic system I/M ready status and drive cycle appears later in this section.

Do not use a test light to diagnose the powertrain electrical systems unless you are specifically instructed by diagnostic procedures. Use the Connector Test Adaptor Kit, J 35616 whenever diagnostic procedures call for probing any of the connectors.

Use the Connector Test Adapter Kit J 35616 for any test that requires probing the ECM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

The control module is designed to withstand normal current draws associated with vehicle operations. Avoid overloading any circuit. When testing for opens or shorts, do not ground or apply voltage to any of the control module circuits unless instructed to do so. Test these circuits by using the digital voltmeter J 39200 only.

Notice: 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.

Notice: 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 vehicle's 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 problem is to eliminate all of the aftermarket electrical equipment from the vehicle. After this is done, if the problem still exists, the problem may be diagnosed in the normal manner.

Notice: In order to prevent possible Electrostatic Discharge damage to the PCM, Do Not touch the connector pins or the soldered components on the circuit board.

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 volts of static electricity can cause damage to some electronic components. By comparison, it takes as much as 4,000 volts 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 use care when handling and testing electronic components.

The underhood Vehicle Emissions Control Information Label contains important emission specifications and setting procedures. In the upper left corner is the exhaust emission information. This identifies the year, the manufacturing division of the engine, the displacement of the engine in liters, the class of the vehicle, and type of fuel metering system. There is also an illustrated emission components and vacuum hose schematic.

This label is located in the engine compartment of every General Motors vehicle. If the label has been removed, it can be ordered from GM Service Parts Operations (GMSPO).

Refer to the General Motors Maintenance Schedule in Maintenance and Lubrication for the maintenance that should be performed to retain the emission control performance.

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

This visual/physical inspection is very important and must be done carefully and thoroughly.

Notice: Lack of basic knowledge of this powertrain when performing diagnostic procedures could result in incorrect diagnostic performance or damage to powertrain components. Do not attempt to diagnose a powertrain problem without this basic knowledge.

A basic understanding of hand tools is necessary in order to effectively use this section of the Service Manual.

You must be familiar with some of the basics of engine operation and electrical diagnosis in order to use this section of the service manual.

Base engine, transmission, and non-emissions subsystem Information can be found in the following areas: