Gasoline engines installed on Mazda 6 vehicles are equipped with an electronic engine management system with multipoint fuel injection
This system ensures compliance with modern standards for toxicity of emissions and evaporation of harmful substances, while maintaining high driving performance and low fuel consumption
The control device in the system is the electronic control unit (ECU, controller).
Based on the information received by the sensors, the ECU calculates the parameters for fuel injection control and ignition timing control.
In addition, in accordance with the embedded algorithm, the ECU controls the operation of the electric motor of the fan of the engine cooling system and the electromagnetic clutch for turning on the air conditioning compressor, performs the function of self-diagnostics of the system elements and notifies the driver of any malfunctions.
If individual sensors and actuators fail, the ECU turns on emergency modes that ensure engine performance.
The amount of fuel supplied by the injectors is determined by the duration of the electrical signal from the ECU
The electronic unit monitors data on the state of the engine, calculates the need for fuel and determines the required duration of fuel supply by the injectors (signal duration).
To increase the amount of fuel supplied, the duration of the signal increases, and to decrease the amount of fuel, it decreases.
The engine management system, along with the electronic control unit, includes sensors, actuators, connectors and fuses.
Electronic control unit (ECU)
The electronic control unit (ECU) is connected by electrical wires to all sensors of the system.
Receiving information from them, the block performs calculations in accordance with the parameters and control algorithm stored in the memory of the programmable read-only memory (PROM), and controls the system's executive devices.
The program version recorded in the PROM memory is indicated by the number assigned to this ECU modification
The control unit detects a fault, identifies and remembers its code, even if the fault is unstable and disappears (for example, due to poor contact).
The engine control system malfunction indicator in the instrument cluster goes out 10 seconds after the failed unit is restored.
After repair, the fault code stored in the memory of the control unit must be erased.
To do this, turn off the power to the unit for 10 seconds (remove the fuse for the power supply circuit of the electronic control unit or disconnect the wire from the negative terminal of the battery).
The unit supplies various sensors and switches of the control system with DC voltage of 5 and 12 volts.
Because the electrical resistance of the power circuits is high, the test lamp connected to the system outputs does not light up.
To determine the supply voltage at the computer terminals, use a voltmeter with an internal resistance of at least 10 MΩ.
The computer is not suitable for repair, in case of failure it must be replaced.
Diagnostic connector
The diagnostic connector is used to display fault codes detected during the operation of the engine management system from the computer memory.
The diagnostic connector is located in the passenger compartment on the left side of the instrument panel under the steering wheel.
You can connect a scanner to the diagnostic socket that reads trouble codes.
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 mounted at the rear of the engine opposite the drive teeth on the flywheel.
The driving teeth are made on the surface of the flywheel at regular intervals.
One tooth is missing to create a synchronization pulse ("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.
As the crankshaft rotates, the teeth change the magnetic field of the sensor, inducing AC voltage pulses.
The control unit determines the crankshaft speed using the sensor signals and sends pulses to the injectors.
If the sensor fails, the engine cannot be started.
Camshaft position sensor
The camshaft position sensor (phase sensor) of the inductive type determines the TDC of the compression stroke of the piston of the 1st cylinder.
The signal from the sensor is used by the electronic control unit and serves to organize phased fuel injection in accordance with the order of operation of the cylinders.
If a malfunction occurs in the circuit of any of the sensors, the ECU stores its code in its memory and turns on the signal lamp.
Coolant temperature sensor
The coolant temperature sensor is installed in the coolant distributor housing at the rear of the engine.
The sensing element of the sensor is a thermistor, the electrical resistance of which changes inversely with temperature.
At a low coolant temperature (-40 °C), the resistance of the thermistor is about 100 kOhm, when the temperature rises to +130 °C, it decreases to 70 Ohm.
The electronic unit supplies the temperature sensor circuit with a constant "reference" voltage.
The voltage of the sensor signal is maximum on a cold engine and decreases as it warms up.
The electronic unit determines the engine temperature from the voltage value and takes it into account when calculating the injection and ignition control parameters.
If the sensor fails or there are violations in its connection circuit, the ECU sets the fault code and remembers it.
In addition to the above, the sensor indirectly serves as a sensor for the coolant temperature indicator in the instrument cluster.
Based on information from this sensor, the electronic engine control unit changes the position of the pointer arrow.
Combined absolute pressure and temperature transmitter
The combined absolute pressure and intake air temperature sensor in the intake manifold is made in the form of a variable resistor sensitive to pressure changes.
It records the change in intake manifold pressure in accordance with changes in load and engine speed.
Depending on the information received from the sensor, the ECU registers the amount of fuel injected and the ignition timing.
Throttle position sensor
The throttle position sensor is made in one piece with the throttle assembly cover.
The sensor is a potentiometer, one end of which is supplied with a "plus" supply voltage (5 V), and the other end is connected to the "ground".
The third output of the potentiometer (from the slider) is the output signal to the electronic control unit.
When the throttle valve is turned (from the action on the control pedal), the voltage at the output of the sensor changes.
It is below 0.5 volts when the throttle is closed. When the damper opens, the voltage at the sensor output rises, with the damper fully open, it should be more than 4 volts.
By monitoring the output voltage of the sensor, the ECU adjusts the fuel supply depending on the throttle opening angle (i.e. at the request of the driver).
The throttle position sensor does not require adjustment, since the control unit perceives idling (i.e. full throttle closing) as a zero mark.
Mass air flow sensor
The mass flow and intake air temperature sensor, mounted on the air filter housing nozzle, is a very important sensor in the electronic engine control system.
Based on its signal, the electronic engine control unit determines the cyclic filling of the cylinders and ultimately corrects the duration of the injector opening pulse and the ignition timing.
Oxygen concentration sensors (lambda probes)
Oxygen concentration sensors (lambda probes) are screwed into the threaded holes of the catalytic converter and exhaust pipe.
Two oxygen concentration sensors are installed on Mazda 6 cars:
- a control sensor designed to control the composition of the air-fuel mixture (at the inlet to the converter);
- a diagnostic sensor designed to evaluate the efficiency of the converter (at the output).
A galvanic cell is located in the metal bulb of the sensor, washed by the exhaust gas flow.
Depending on the oxygen content in the exhaust gases, the combustion of the air-fuel mixture changes the voltage of the sensor signal.
Sensors differ in parameters and have different markings.
If at least one of the oxygen concentration sensors is defective, the toxicity of exhaust gases can increase dramatically, and fuel consumption will increase.
For ease of replacement, the sensors differ in the color of the pads.
The sensor harness block at the inlet to the converter (control) is green, and at the outlet of the converter (diagnostic) it is purple.
Information from each sensor enters the control unit in the form of low (from 0.1 V) and high (up to 0.9 V) level signals.
At a low level signal, the control unit receives information about a high oxygen content.
A high level signal indicates a low oxygen content in the exhaust gases.
Constantly monitoring the voltage of the sensor signal, the control unit adjusts the amount of fuel injected by the injectors.
When the sensor signal at the input to the converter is low (lean air-fuel mixture), the amount of fuel supplied increases, and when the signal is high (rich mixture), it decreases.
If the difference between the signal levels of the sensors at the inlet and outlet of the converter is less than the values admissible in this mode of operation, the control unit identifies a malfunction of the catalytic converter.
Knock sensor
A knock sensor attached to the top of the cylinder block in the area between cylinders 2 and 3 detects abnormal vibrations (knock) in the engine.
The sensing element of the knock sensor is a piezoelectric plate.
During detonation, voltage pulses are generated at the output of the sensor, which increase with increasing intensity of detonation impacts. The ECU, based on the sensor signal, regulates the ignition timing to eliminate detonation flashes of fuel.
In the course of operation, the ECU also uses the vehicle speed data received from the anti-lock braking system (ABS) control unit.
Before removing any fuel injection control system components, disconnect the wire from the negative terminal of the battery.
Do not start the engine if the cable lugs on the battery are loose.
Never disconnect the battery from the vehicle's electrical system while the engine is running.
When charging the battery, disconnect it from the car's on-board network.
Do not expose the ECU to temperatures above 65°C in working condition and above 80°C in non-working condition (for example, in a drying chamber). It is necessary to remove the computer from the car if this temperature is exceeded.
Do not disconnect or connect wires to the computer while the ignition is on.
Before carrying out electric welding work on the car, disconnect the wires from the battery and the wiring harness pads from the computer.
Perform all voltage measurements with a digital voltmeter with an internal resistance of at least 10 mΩ.
Electronic components used in the fuel injection system are designed for very low voltage, so they can easily be damaged by electrostatic discharge.
To prevent damage to the computer, do not touch its terminals with your hands.
To diagnose the engine control system in all cases, a special scanner is required, so if a system malfunction occurs, contact a specialized service.