Sensors can detect physical quantities in various states and convert physical quantities into electrical quantities for transport. It is like a human sensory organ that correctly detects the physical quantity under all conditions of the engine and inputs it into a control computer circuit. Therefore, the sensor is to determine the quality of the engine electronic control system key components.

1, speed sensor

Speed ​​sensor is usually mounted on the distributor or the engine, it can detect the crank angle. A breakdown, will destroy the ignition system, so that the engine can not work. Because most of the speed sensor is magnetic pulse type, it can send a weak electrical signal, the detection can use multimeter or oscilloscope;

Troubleshooting

(1) to determine the basis

A good speed sensor with a multimeter AC voltage measurement rotating crankshaft, the output voltage should be in the range of 1.5 ~ 3.0V. If there is no AC voltage input or output voltage does not meet the requirements, then the sensor is damaged, it should be replaced;

In the engine does not turn, the sensor coil resistance check. Check the method is to remove the wire plug, with a multimeter resistance measurement, the resistance should be in the range of 250 ~ 1500Ω;

(2) treatment

If you suspect the sensor internal wire poor contact, the multimeter can be placed in the resistance file and the sensor wire is connected, and then shake the wire to see if the multimeter pointer is swung, if the wobble that the sensor internal wire poor contact should be immediately ruled out;

2, knock sensor

Knock sensors are mounted directly on the cylinder and require higher reliability or stability due to direct temperature changes or vibrations on the engine block. Its overhaul tool “multimeter”;

Troubleshooting

(1) to determine the basis

When the engine is running, connect the sensor wire slowly to increase the speed, meanwhile measure the AC voltage with the multimeter. If the voltage value increases subsequently, it indicates that the sensor may be faulty.

When the engine is running, connect the sensor wire, gently tap the intake manifold with a small plastic hammer, and measure it with the AC voltage of the multimeter. If the voltage indicator fluctuates, then the sensor is faulty;

(2) treatment

Turn the ignition switch to the OFF position, remove the sensor connector after 10s, turn the ignition switch ON and use a multimeter to measure the DC voltage between the signal output on the on-board harness connector and the circuit terminals. The value should be Meet the regulations (specific values, please refer to the maintenance manual), otherwise the line may be faulty;

3, water temperature sensor

Water temperature sensor is the sensor to measure the temperature of the engine cooling water, which is made up of thermistor and installed on the engine cooling water channel. When the cooling water temperature changes, the resistance changes. In electronically controlled fuel injection systems, this signal is fed into the electronic control unit and the amount of fuel injected can be corrected for the cooling water temperature.

Troubleshooting

(1) to determine the basis

The precision of the water temperature sensor has a certain impact on the amount of fuel injection. When the mixture is too rich or too dilute, you should first check the water temperature sensor, and then check the other sensors;

(2) treatment

During the inspection, the water temperature sensor can be disassembled and placed in a teapot to heat test it. The resistance at different water temperatures is measured. When the water temperature is 20 ℃, the resistance value should be about 2 ~ 3KΩ, 80 ℃ Should be about 0.2 ~ 0.4kΩ resistance.If the measurement results do not meet the requirements, the water temperature sensor should be replaced;

4, intake temperature sensor

The intake air temperature sensor is a sensor measuring the temperature of the intake air of the engine. The purpose of measuring the intake air temperature is to determine the density of the intake air of the engine and to correct the fuel injection amount according to the air density change caused by the temperature change of the intake air. It is usually installed in the air flow meter or air intake manifold after the grid; performance: fuel consumption, acceleration weakness, black smoke exhaust pipe.

Troubleshooting

(1) to determine the basis

Due to its structure and water temperature sensor is basically similar, check the water temperature sensor can be used to check the method. Under normal circumstances, when the temperature is 20 ℃, the resistance is about 2 ~ 3kΩ, 60 ℃, the resistance is about 0.4 ~ 0.7kΩ. Check engine air flow meter data flow, out of range. Fuel injection pulse acceleration increases, but the basic rate of increase of air flow is not, so that air-fuel ratio will be inappropriate, inevitably accelerate weakness.

(2) treatment

If the measurement does not meet the requirements, replace the sensor. When installed in the air flow meter inlet temperature sensor is damaged should replace the air flow meter, cleaning the throttle body, replace the original air filter.

5, intake pressure sensor

The electronically controlled fuel injection system which uses the speed / density method to detect the intake air volume indirectly measures the amount of air sucked by the engine by using an intake manifold pressure sensor, and usually checks the sensor power supply voltage and output voltage during the test.

Troubleshooting

(1) Check the power supply voltage

Remove the harness connector of the pressure sensor on the intake manifold, turn the ignition switch ON, and then measure the voltage between the power terminals on the harness connector with the voltage scale of the multimeter Please check the service manual of the repaired vehicle) Otherwise, the electric control harness should be replaced or repaired;

(2) the output voltage check

Remove the sensor and intake manifold connected to the vacuum hose, so that the sensor communicates directly with the atmosphere, then the ignition switch (ON) position, with the voltmeter in the control unit wiring harness plug measuring the sensor output voltage, then A vacuum is applied to the sensor, and its output voltage under different vacuum can be measured. The value of the voltage should decrease with the increase of the vacuum density. The change of the voltage should be in accordance with the technical parameters or the sensor should be replaced.

6, oxygen sensor

Oxygen sensor installed in the engine exhaust pipe, the role is to detect the concentration of oxygen in the exhaust pipe and convert it into a voltage signal or resistance signal, so that the electronic control unit in accordance with this signal to control the mixture of light / light;

Engine oil consumption is too large, serious black smoke. Check the engine with a fault diagnostic tool, observe the data stream, the oxygen sensor voltage changes frequency of 10 to 20 times / s, which is the ideal working condition, if less than 10 times / s, you can initially determine the oxygen sensor failure, if Is no change in the voltage of 0.45V, then you can determine the oxygen sensor is damaged, the signal is interrupted.

Troubleshooting

(1) Check the power supply voltage

Oxygen sensor has two types of heating and non-heating, heating type should check its heating resistance;

Check the heating resistor: Use a multimeter to measure the resistance between the two terminals of the heater in the terminal, its normal value should be 4 ~ 40kΩ. Otherwise it should replace its oxygen sensor;

Oxygen Sensor Feedback Voltage Detection: Remove the oxygen sensor harness connector and connect the voltmeter positive test lead directly to the oxygen sensor feedback voltage output. Start the engine, suddenly depressing or relaxing the accelerator pedal to change the mixture concentration, suddenly depresses the accelerator pedal, the mixture is thicker, the feedback voltage should rise; Suddenly relax, the mixture should be thinner voltage drop, or that the sensor Invalid, it should be replaced;

Visual inspection: remove the sensor from the exhaust pipe, check the ventilation holes on the case is blocked, whether the ceramic core rupture. If damaged, replace immediately

(2) the output voltage check

Replace the oxygen sensor, re-test with a fault diagnostic tester, test normal, troubleshooting.

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