The coolant temperature sensor is a thermistor (a resistor whose resistance changes with temperature). The sensor is screwed into the thermostat housing and connected to the ECU. At low temperatures, the sensor resistance is high, and at high temperatures, it is low (table 10.5).
The ECU calculates the coolant temperature based on the voltage drop across the sensor. When the engine is cold, the voltage drop is high, and when it is warm, it is low.
Table 10.5. Coolant temperature sensor resistance versus temperature
Coolant temperature affects most of the characteristics controlled by the ECU.
To replace the sensor you will need a 19 key.
1. Disconnect the wire from the negative terminal of the battery.
2. Partially drain the coolant from the radiator.
3. For ease of operation, remove the air filter (see "Removing and installing the air filter").
4. Press the plastic retainer...
5. ...and disconnect the wiring harness connector from the coolant temperature sensor.
6. Loosen the sensor tightening with a wrench...
7. ...and unscrew it from the thermostat housing.
8. Cool the sensor to ambient temperature. Connect the tester in ohmmeter mode to the sensor terminals and measure its resistance. Measure the current air temperature with a thermometer and compare the obtained values with the table. 10.5. If the resistance deviates from the norm, replace the sensor.
9. To measure the resistance at the sensor terminals at different temperature conditions, lower the sensor into hot water and check the change in its resistance as the water cools, monitoring the water temperature with a thermometer. The nominal resistance values at different temperatures are shown in the table. 10.5.
10. Install the sensor in the reverse order of removal.
11. Fill with coolant.
Knock sensor, attached to the top of the cylinder block, detects abnormal vibrations (detonation strikes) in the engine.
The sensitive element of the sensor is a piezoelectric crystal plate. When detonation occurs, voltage pulses are generated at the sensor output, which increase with increasing intensity of detonation shocks. The ECU, based on the sensor signal, regulates the ignition timing to eliminate detonation flashes of fuel.
To replace the sensor you will need a 13 mm wrench.
1. Disconnect the wire from the negative terminal of the battery.
2. Press the metal lock of the wiring harness connector...
3. ...and disconnect the connector from the knock sensor. For clarity, the crankcase ventilation hose has been removed.
4. Loosen the knock sensor mounting bolt with a wrench...
5. ...and, having unscrewed the bolt by hand, remove it together with the knock sensor.
Note: Please pay attention to the marking of the sensor in order to purchase a similar knock sensor for replacement.
6. Install the sensor in the reverse order, screwing in its mounting bolt and tightening it to a torque of 10.4–24.2 N·m.
Mass Air Flow Sensor (MAF) located between the air filter and the air supply hose.
The sensor signal is a DC voltage whose value depends on the amount of air passing through the sensor.
The MAF has a built-in air temperature sensor, the sensitive element of which is a thermistor installed in the air flow. At low temperature the resistance of the sensor is high, and at high temperature it is low (table 10.6).
Table 10.6. Dependence of the air temperature sensor resistance on the intake air temperature (permissible error 10%)
If the air temperature sensor is faulty, the ECU stores the error code in its memory and turns on the warning light, and replaces the readings of the faulty sensor with a fixed air temperature value of 33°C.
To replace the sensor you will need: a 10 mm wrench and a Phillips-head screwdriver.
1. Disconnect the wire from the negative terminal of the battery.
2. Using a screwdriver or finger, press the plastic latch from below...
3. ...disconnect the wiring harness connector from the mass air flow sensor.
4. Loosen the air supply hose clamp...
5. ...and disconnect the sleeve from the sensor.
6. Unscrew the two mounting screws...
7. ...and remove the sensor from the air filter.
8. Remove the rubber gasket and carefully inspect the condition of its edges, as damage to them may result in air being sucked in bypassing the air filter. When driving, the air contains many small mechanical particles that can damage the MAF and, as a result, lead to interruptions in engine operation.
9. Before installing the sensor, first put the rubber sealing gasket on it and only then fix the sensor on the air filter.
Vehicle speed sensor installed on the gearbox. When the drive wheels rotate, the speed sensor generates 6 pulses per 1 m of the vehicle's travel, and the ECU determines the vehicle's speed based on the frequency of the pulses.
To replace the sensor you will need a 10 mm wrench.
1. Disconnect the wire from the negative terminal of the battery.
2. Press the latch...
3. ...and disconnect the wiring harness from the speed sensor.
4. Unscrew the nut of the speed sensor mounting stud...
5. ...and remove the sensor from the gearbox housing.
6. Install the sensor in the reverse order of removal.
Throttle Position Sensor (TPS) mounted on the side of the throttle assembly and connected to the throttle shaft. 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 0.6 V. When the valve opens, the voltage at the sensor output increases and when the valve is fully open, it should be more than 4.4 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 "CHECK ENGINE" indicator light and calculates the expected value of the throttle opening angle based on the crankshaft speed and the MAF signal.
To replace the sensor, you must do the following.
1. Disconnect the wire from the negative terminal of the battery.
2. Press the latch...
3. ...and disconnect the wiring harness connector from the sensor terminals.
4. Remove the two mounting screws...
5. ...and remove the throttle position sensor from the throttle body.
6. Install the sensor in the reverse order of removal. Pay attention to the condition of the sealing foam ring: if it is damaged, replace it with a new one.
Idle speed control (ISC) regulates the crankshaft speed in idle mode by controlling the amount of air supplied bypassing the closed throttle valve. It consists of a two-pole stepper motor and a cone valve connected to it. The valve extends or retracts according to the ECU signals. Fully extended regulator needle (which corresponds to 0 steps) blocks the air flow. When the needle is pushed in, an air flow is provided proportional to the number of steps the needle moves away from the seat.
Replacing the idle speed control valve is described in section. "Engine" (see "Replacing the idle speed control valve", p. 134).
Crankshaft position sensor inductive type, designed to measure the rotation speed and position of the crankshaft. The sensor is installed on the oil pump cover opposite the timing disk on the generator drive pulley. The timing disk is a toothed wheel with 58 equally spaced (6°) depressions. With this pitch, 60 teeth are placed on the disk, two teeth are cut to create a synchronization pulse (the "reference" pulse), which is necessary to coordinate the controller's operation 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 installation gap between the sensor core and the disk tooth should be within (1±0.2) mm. The ECU sends pulses to the injectors based on the sensor signals.
To replace the sensor you will need a 10 mm wrench.
1. Disconnect the wire from the negative terminal of the battery.
2. Press the latch...
3. ...and disconnect the wiring harness from the crankshaft position sensor.
4. Unscrew the mounting bolt...
5. ...and remove the sensor from its mounting bracket.
6. Measure the resistance of the sensor. The resistance of a working sensor should be 500–700 Ohm. If the tester readings are significantly lower, then there is probably an interturn short circuit in the winding, and if, on the contrary, it is high or the tester shows infinity (see photo), then the contacts inside the sensor are broken or there is a break in the winding of the induction coil. In both the first and second cases, the sensor must be replaced.
7. Install the sensor in the reverse order of removal.
Oxygen concentration control sensor it is used in the fuel injection system with feedback and is installed in the upper part of the catalytic converter. To adjust the calculations of the injection pulse duration, information about the presence of oxygen in the exhaust gases is used; this information is provided by the control oxygen concentration sensor. The oxygen contained in the exhaust gases reacts with the oxygen sensor, creating a potential difference at the sensor output. It varies from approximately 0.1 V (high oxygen content - lean mixture) to 0.9 V (low oxygen content - rich mixture).
For normal operation, the sensor temperature must be at least 300°C. Therefore, a heating element is built into the sensor for quick warming up after starting the engine.
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.
To replace the oxygen concentration control sensor, you will need a 22 mm wrench.
1. Disconnect the wire from the negative terminal of the battery.
2. Press the latch...
3. ...and disconnect the oxygen sensor control wiring harness connector from the engine harness.
4. Disconnect the oxygen concentration sensor control wire harness holder from the steering gear heat shield.
5. Unscrew the sensor from the exhaust manifold...
6. ...and remove from the car.
Note: Use special reinforced hex keys to remove the sensor. They can look like open-end wrenches or be in the form of a high socket head with a split sector for threading a wire harness through it.
7. Install the sensor in the reverse order of removal, after lubricating the threaded part of the sensor with graphite grease.
Oxygen Concentration Diagnostic Sensor it is installed in the catalytic converter behind the neutralizer, operates on the same principle as the control sensor, and is completely interchangeable with it. The signal generated by the diagnostic oxygen concentration sensor indicates the presence of oxygen in the exhaust gases after the catalytic converter. If the neutralizer is working properly, the diagnostic sensor readings will differ significantly from the control sensor readings.
Replacing the diagnostic oxygen concentration sensor is carried out in the same way as replacing the control sensor.
Phase sensor installed on the rear cover of the camshaft drive. Its operating principle is based on the Hall effect. A timing disk with a special groove (ledge) is fixed by spot welding on the camshaft pulley (intake). When the disk passes through the sensor slot, a low-level voltage pulse is sent from the sensor to the ECU (approximately 0 V), and when the step of the reference disk hits the "measuring" area of the sensor, a "reference" voltage pulse occurs on the ECU (about 5 V), which corresponds to the position of the piston of the 3rd cylinder in the compression stroke.
To replace the phase sensor, you will need a 10 mm socket wrench.
1. Disconnect the wire from the negative terminal of the battery.
2. Press the latch...
3. ...and disconnect the wiring harness connector from the phase sensor.
4. Unscrew the two sensor mounting bolts...
5. ...remove the sensor (for clarity, the unscrewing of bolts with an open-end wrench on a removed and partially disassembled engine is shown).
6. Install the sensor in the reverse order of removal.
Rough Road Sensor installed in the engine compartment on the right mudguard cup. The operating principle of the sensor is based on the piezoelectric effect. When driving on an uneven road, the variable load affects the angular velocity of the crankshaft. The crankshaft speed variations are similar to the variations that occur during misfires.
The rough road sensor measures the amplitude of the vehicle body vibrations and sends a signal to the controller. When the signal threshold is exceeded, the controller disables the misfire diagnostic function.
To remove the rough road sensor, you will need a Phillips-head screwdriver.
1. Disconnect the wire from the negative terminal of the battery.
2. Compress the spring clip...
3. ...and disconnect the wiring harness connector from the sensor terminals.
4. Remove the two screws securing the sensor to the bracket...
5. ...and remove the sensor.
6. Install the sensor in the reverse order of removal.