Design Features of the Engine Management System (Chevrolet Cruze J300)

Engines installed on Chevrolet Cruze vehicles are equipped with an electronic engine management system (EEMS) with distributed fuel injection. This system works together with an exhaust gas neutralizer, a fuel vapor recovery system and ensures compliance with environmental standards while maintaining high dynamic qualities and low fuel consumption.

The electrical diagram of the engine control system is given at the end of the book.

Warnings: Before removing any ECM components, disconnect the negative battery cable.

Do not start the engine if the battery cable terminals are not tightly tightened.

Never disconnect the battery from the vehicle's electrical system while the engine is running.

When charging the battery, disconnect it from the vehicle's electrical system.

Do not expose the electronic control unit (ECU) to temperatures above 65°C when operating and above 80°C when not operating (for example, in a drying chamber). If this temperature is exceeded, the ECU must be removed from the vehicle.

Do not disconnect or connect the wiring harness connectors to the ECU with the ignition on.

Before performing arc welding on a vehicle, disconnect the wires from the battery and the wire connectors from the ECU. Perform all voltage measurements with a digital voltmeter with an internal resistance of at least 10 MOhm.

The amount of fuel supplied by the injectors is regulated by an electrical pulse signal from the ECU. It monitors engine condition data, calculates fuel requirements and determines the required duration of fuel supply by the injectors (pulse duration - duty cycle). To increase the amount of fuel supplied, the ECU increases the pulse duration, and to reduce the fuel supply, it shortens it

The ECU evaluates the results of its calculations and commands, remembers the modes of recent operation and acts in accordance with them. "Self-learning" or adaptation of the ECU is a continuous process, but the corresponding settings are saved in the RAM of the electronic unit until the first power-off of the ECU.

The ECU controls the fuel supply either synchronously, i.e. at a certain position of the crankshaft, or asynchronously, i.e. independently or without synchronization with the rotation of the crankshaft. Synchronous fuel injection is the most frequently used mode. Asynchronous fuel injection is used mainly in the engine start mode. The ECU switches on the injectors sequentially. Each of the injectors is switched on every 720° of crankshaft rotation. This method allows for more accurate dosing of fuel to the cylinders and a reduction in the toxicity of exhaust gases.



The amount of fuel supplied is determined by the engine condition, i.e. its operating mode. These modes are provided by the ECU and are described below.

When the engine crankshaft begins to rotate with the starter, the first pulse from the crankshaft position sensor causes a pulse from the ECU to turn on all injectors at once, which allows the engine to start faster.

The initial fuel injection occurs each time the engine is started. The duration of the injection pulse depends on the temperature. On a cold engine, the injection pulse increases to increase the amount of fuel, on a warm engine, the pulse duration decreases. After the initial injection, the ECU switches to the appropriate injector control mode.

Start mode. When the ignition is turned on, the ECU switches on the fuel pump relay, which creates pressure in the fuel supply line to the fuel rail.

The ECU checks the signal from the coolant temperature sensor and determines the amount of fuel and air required for starting.

When the engine crankshaft starts to turn, the ECU generates a phased pulse to turn on the injectors, the duration of which depends on the signals from the coolant temperature sensor. On a cold engine, the pulse duration is longer (to increase the amount of fuel supplied), and when warmed up - less.

Enrichment mode during acceleration

The ECU monitors sudden changes in the throttle position (by signal from the throttle position sensor), as well as the absolute pressure sensor signal and provides additional fuel supply by increasing the injection pulse duration. The enrichment mode during acceleration is used only to control fuel supply in transient conditions (when moving the throttle valve).

Fuel shut-off mode during engine braking

When braking with the engine with the gear and clutch engaged, the ECU can completely disable the fuel injection pulses for short periods of time. The fuel supply is switched off and on in this mode when certain conditions are created for the coolant temperature, crankshaft speed, vehicle speed, and throttle opening angle.

Supply voltage compensation

When the supply voltage drops, the ignition system may produce a weak spark and the mechanical movement of "opening" the injector may take longer. The ECU compensates for this by increasing the energy accumulation time in the ignition coils and the duration of the injection pulse.

Accordingly, when the battery voltage increases (or voltage in the vehicle's on-board network) The ECU reduces the energy accumulation time in the ignition coils and the injection duration.

Fuel Shut-Off Mode

When the engine stops (ignition off) the fuel is not supplied by the injector, thus eliminating spontaneous ignition of the mixture in an overheated engine. In addition, pulses to open the injectors are not supplied if the ECU does not receive reference pulses from the crankshaft position sensor, i.e. this means that the engine is not running.

The fuel supply is also cut off when the maximum permissible engine crankshaft speed is exceeded to protect the engine from running at unacceptably high speeds.

Electronic control unit

Electronic control unit (ECU, controller) the engine is located in the central part of the air intake box and is the control center of the electronic engine management system. It continuously processes information from various sensors and controls systems that affect the toxicity of exhaust gases and the vehicle's performance.

The following information is received by the ECU:

• crankshaft position and speed;
• camshaft position;
• coolant temperature;
• intake air temperature and pressure;
• accelerator pedal position;
• throttle position;
• oxygen content in exhaust gases;
• presence of detonation in the engine;
• car speed;
• voltage in the vehicle's on-board network;
• request to turn on the air conditioner.

Based on the information received, the ECU controls the following systems and devices:

• fuel supply (injectors and fuel pump);
• air supply (throttle opening degree);
• ignition system;
• adsorber of the gasoline vapor recovery system;
• engine cooling system fan;
• air conditioning compressor clutch;
• diagnostic system.

The ECU turns on the output circuits (injectors, various relays, etc.) by shorting them to "ground" through the output transistors. The only exception is the fuel pump relay circuit. The fuel pump is connected through a power relay. In turn, the relay winding is controlled by the ECU by shorting one of the terminals to "ground".

The ECU has a built-in diagnostic system. It can recognize malfunctions in the ECU, warning the driver about them through the malfunction indicator in the engine management system. In addition, the ECU stores diagnostic codes indicating the malfunction of a specific element of the system and the nature of this malfunction to help specialists in diagnostics and repair.

Diagnostic connector

The diagnostic connector is used to exchange data with the ECU and is located on the left side under the instrument panel. A scanning device is connected to the diagnostic connector to read error information stored in the ECU memory, to check sensors and actuators in real time, to control actuators and reprogram the ECU.

The following types of memory are included in the ECU:

• programmable read-only memory (EPROM);
• random access memory (RAM);
• electrically reprogrammable memory (ERPROM).

Programmable Read Only Memory (PROM) - It contains a general program that contains a sequence of operating instructions (control algorithms) and various calibration information. This information is the data for controlling injection, ignition, idle speed, etc., which depend on the weight of the vehicle, the type and power of the engine, the gear ratios of the transmission and other factors. The EPROM is also called a calibration memory device. The contents of the EPROM cannot be changed after programming. This memory does not require power to save the information recorded in it, which is not erased when the power is turned off, i.e. this memory is non-volatile.

Random Access Memory (RAM)

This is the ECU "notebook". The microprocessor of the unit uses it for temporary storage of measured parameters for calculations and intermediate information. The microprocessor can enter data into it or read it as needed.

The RAM chip is mounted on the controller's printed circuit board. This memory is volatile and requires uninterruptible power supply to be saved. When the power supply is interrupted, the diagnostic trouble codes and calculated data contained in the RAM are erased.

Electrically reprogrammable memory (ERPROM)

Used for temporary storage of codes and passwords for the vehicle's anti-theft system (immobilizer). The password codes received by the ECU from the immobilizer control unit are compared with the codes stored in the EEPROM, as a result of which the engine starting is permitted or prohibited.

The EEPROM records such vehicle operating parameters as the total vehicle mileage, total fuel consumption and engine operating time.

The ERPZU also registers some malfunctions of the engine and the vehicle:

• engine overheating time;
• engine operating time on low octane fuel;
• engine operating time exceeding the maximum permissible rotation speed;
• the time the engine is running with misfires of the fuel-air mixture, the presence of which is indicated by the engine management system indicator;
• engine operating time with a faulty knock sensor;
• engine operating time with faulty oxygen concentration sensors;
• time of driving the vehicle at a speed exceeding the maximum permitted speed during the running-in period;
• the time the vehicle is moving with a faulty speed sensor;
• number of times the battery is disconnected with the ignition switch on.

The EEPROM is a non-volatile memory and can store information without power being supplied to the controller.

Crankshaft position sensor

The inductive type crankshaft position sensor is designed to synchronize the operation of the electronic control unit with the TDC of the pistons of the 1st and 4th cylinders and the angular position of the crankshaft.

The sensor is installed at the rear of the engine cylinder block opposite the timing disk on the crankshaft. The timing disk is a toothed wheel with 58 grooves, 57 of which are spaced at 6° intervals. The last groove is made wider to create a synchronization pulse (the "reference" pulse), which is necessary to coordinate the operation of the control unit with the TDC of the pistons in the 1st and 4th cylinders.

When the crankshaft rotates, the sensor's magnetic field changes, inducing AC voltage pulses. The control unit determines the crankshaft rotation frequency based on the sensor's signals and issues pulses to control the engine.

A malfunction of this sensor causes a complete failure of the engine management system: without its signal, the engine cannot be started.

Manifold Absolute Pressure Sensor

The absolute pressure sensor in the intake pipe converts the vacuum in this pipe into an electrical voltage, by the value of which the ECU determines the engine load. The sensor is installed on the intake pipe and is connected to its cavity by a rubber tube. The output voltage of the sensor changes in accordance with the pressure in the intake pipe - from 4.9 V (with the throttle fully open) up to 0.3 V (with the damper closed). When the engine is not running, the control unit determines the atmospheric pressure from the sensor voltage and adapts the injection control parameters to the specific altitude. The atmospheric pressure values stored in the memory are periodically updated during uniform vehicle movement and during full throttle opening.

Intake air temperature sensor

The intake air temperature sensor is screwed into the air supply hose opening near the air filter. The sensor is a thermistor with a negative temperature coefficient of resistance. Based on the air temperature information from the sensor, the controller regulates the amount of fuel injected.

The resistance of the air temperature sensor at the sensor terminals is checked under various temperature conditions.

Phase sensor

The phase sensor is installed in the front part of the cylinder head between the toothed pulleys of the camshafts. Its operating principle is based on the Hall effect. The sensor determines the TDC of the compression stroke of the piston of the 1st cylinder. The sensor signal is used by the controller to organize phased fuel injection in accordance with the order of operation of the cylinders. If a circuit malfunction occurs, the controller stores its code in its memory and turns on the engine management system indicator.

Coolant temperature sensor

The coolant temperature sensor is installed on the right side of the cylinder head between the first and second cylinders. The sensor is a thermistor with a negative temperature coefficient: the electrical resistance of the sensor decreases with increasing temperature. The ECU processes the sensor signal and sets the optimal enrichment of the working mixture when the engine warms up.

The electronic unit supplies the temperature sensor circuit with a constant "reference" voltage. The sensor signal voltage is maximum when the air in the intake pipe is cold, and decreases as its temperature increases. Based on the voltage value, the ECU determines the air temperature at the intake and makes adjustments when calculating the ignition timing. If the sensor fails or there are problems in its connection circuit, the ECU sets a fault code and stores it. If the ECU continues to issue a fault code with good contact connections in the wiring, replace the air temperature sensor.

Knock sensor

The knock sensor is attached to the top of the cylinder block and detects abnormal vibrations (detonation strikes) in the engine.

The sensor's sensitive element is a piezoelectric crystal plate. During detonation, voltage pulses are generated at the sensor's output, which increase with the intensity of detonation shocks. The controller, based on the sensor's signal, regulates the ignition advance to eliminate detonation flashes of fuel.

Throttle position sensor

The throttle position sensor (TPS) is mounted on the side of the throttle assembly (under the lid) and is connected to the throttle axis.

It is a potentiometer, to one end of which the "plus" of the supply voltage (5 V) is supplied, its other end is connected to the "ground". From the third output of the potentiometer (from the slider) there is an output signal to the ECU. When the throttle valve turns (from the impact on the control pedal), the voltage at the sensor output changes. When the throttle valve is closed, it is below 0.5 V. When the valve opens, the voltage at the sensor output increases and when the valve is fully open, it should be more than 4 V. By monitoring the sensor output voltage, the ECU adjusts the fuel supply depending on the throttle valve opening angle (i.e. at the driver's discretion). The TPS does not require adjustment, since the electronic unit perceives idle speed (i.e. complete closing of the throttle valve) as a zero mark.

If the throttle sensor fails, the ECU stores the sensor fault code in its memory, turns on the engine management system indicator lamp and calculates the expected value of the throttle opening angle based on the crankshaft speed and signals from the temperature and absolute air pressure sensors in the intake manifold.

Oxygen concentration control sensor

The control oxygen concentration sensor is used in the closed-loop injection system and is installed in the exhaust manifold. Information about the presence of oxygen in the exhaust gases is used to adjust the calculations of the injection pulse duration; this information is provided by the control oxygen concentration sensor. The oxygen contained in the exhaust gases reacts with the sensor, creating a potential difference at the sensor output. It changes from approximately 0.1 V (high oxygen content - lean mixture) up to 1 V (low oxygen - rich mixture).

By monitoring the output voltage of the oxygen concentration sensor, the controller determines which command to send to the injectors to adjust the composition of the working mixture. If the mixture is lean (low potential difference at the sensor output), then the controller gives a command to enrich the mixture; if the mixture is rich (high potential difference) - to lean the mixture.

Oxygen Concentration Diagnostic Sensor

The diagnostic oxygen concentration sensor is installed in the intake pipe after the catalytic converter, and works on the same principle as the control sensor. The signal generated by the diagnostic oxygen concentration sensor indicates the presence of oxygen in the exhaust gases after the catalytic converter. If the catalytic converter is working properly, the readings of the diagnostic sensor will differ significantly from the readings of the control sensor,