Common faults and inspection methods of oxygen sensors

China Education Equipment Purchasing Network News: According to the recent news from Dahe.com, oxygen sensors are an indispensable component in engines that use three-way catalytic converters to reduce exhaust pollution. As the air-fuel ratio of the mixed gas deviates from the theoretical air-fuel ratio, the purification capacity of the three-way catalyst for CO, HC and NOX will drop sharply. The ECU sends a feedback signal, and then the ECU controls the increase or decrease of the fuel injection amount of the injector, thereby controlling the air-fuel ratio of the mixture to be near the theoretical value.

At present, there are two kinds of practical oxygen sensors: zirconia type oxygen sensor and titania type oxygen sensor. The common oxygen sensor is divided into single lead, double lead and three leads; single lead is zirconia oxygen sensor; double lead is titania oxygen sensor; three leads are heated zirconia oxygen sensor In principle, the three-lead oxygen sensor can not be used instead.

Once the oxygen sensor fails, the computer of the electronic fuel injection system will not be able to obtain information on the oxygen concentration in the exhaust pipe, so it cannot feedback control the air-fuel ratio, which will increase the engine fuel consumption and exhaust pollution, and the engine will have unstable idle speed Failure phenomena such as lack of fire and surge. Therefore, the fault must be eliminated or replaced in time.

1. Common faults of oxygen sensor

1. Oxygen sensor poisoning

Oxygen sensor poisoning is a failure that often occurs and is difficult to prevent, especially for cars that often use leaded gasoline. Even new oxygen sensors can only work for thousands of kilometers. If it is only mild lead poisoning, and then use a box of lead-free gasoline, the lead on the surface of the oxygen sensor can be eliminated and it can be restored to normal work. However, due to the excessively high exhaust temperature, lead intrudes into its interior, hinders the diffusion of oxygen ions, and makes the oxygen sensor ineffective. At this time, it can only be replaced.

In addition, silicon poisoning of oxygen sensors is also a common occurrence. Generally speaking, the silicon dioxide produced by the burning of silicon compounds in gasoline and lubricating oil, and the silicone rubber gaskets that use improperly emitted silicone gas will invalidate the oxygen sensor, so use good quality fuel and lubricating oil . Rubber gaskets should be selected and installed correctly during repairs. Do not apply solvents and anti-sticking agents other than those specified by the manufacturer to the sensor.

2. Carbon deposit

Due to the poor combustion of the engine, carbon deposits are formed on the surface of the oxygen sensor, or deposits such as oil or dust inside the oxygen sensor will block or block the outside air from entering the oxygen sensor, causing the signal output by the oxygen sensor to be inaccurate, and the ECU cannot be timely Correct the air-fuel ratio. Carbon deposition is mainly caused by increased fuel consumption and a significant increase in emission concentration. At this time, if the sediment is removed, normal work will resume.

3. Oxygen sensor ceramic chipping

The ceramic of the oxygen sensor is hard and brittle, and it can be broken and damaged by being hit with a hard object or blown with a strong air flow. Therefore, special care should be taken when handling, and if problems are found, replace them in time.

4. Heater resistance wire is blown

For the heated oxygen sensor, if the heater resistance wire is ablated, it is difficult to make the sensor reach the normal operating temperature and lose its function.

5. The internal circuit of the oxygen sensor is disconnected.

Second, the inspection method of the oxygen sensor

1. Check the resistance of the oxygen sensor heater

Unplug the oxygen sensor harness and measure the resistance between the heater terminal and the grounding terminal in the oxygen sensor terminal with a multimeter resistance file. The resistance value is 4-40Ω.

If the standard is not met, the oxygen sensor should be replaced.

2. Measurement of the feedback voltage of the oxygen sensor

When measuring the feedback voltage of the oxygen sensor, the harness plug of the oxygen sensor should be unplugged, and a thin wire is drawn from the feedback voltage output terminal of the oxygen sensor according to the circuit diagram of the vehicle model, and then the harness plug is inserted. The feedback voltage is measured on the line.

When detecting the feedback voltage of the oxygen sensor, it is best to use a pointer multimeter with a low range and high impedance. The specific detection methods are as follows:

1) Warm up the engine to normal working temperature;

2) Connect the negative test lead of the multimeter voltage file to E1 or the negative electrode of the battery in the fault detection socket, the positive test lead to the OX1 or OX2 jack in the fault detection socket, or the number on the plug of the oxygen sensor harness |

3) Let the engine keep running at a speed of about 2500r / min, at the same time check whether the voltmeter pointer can swing back and forth between 0-1V, and record the number of times the voltmeter pointer swings within 10s. Under normal circumstances, as the feedback control progresses, the feedback voltage of the oxygen sensor will continuously change around 0.45V, and the number of feedback voltage changes within 10s should be no less than 8 times. If it is less than 8 times, it means that the oxygen sensor or feedback control system is not working properly. The cause may be carbon deposits on the surface of the oxygen sensor, which reduces the sensitivity. In this regard, the engine should be run at 2500r / min for about 2min to remove carbon deposits on the surface of the oxygen sensor, and then check the feedback voltage. If the pointer of the voltmeter still changes slowly after removing the carbon deposit, it means that the oxygen sensor is damaged, or the computer feedback control circuit is faulty.

4) Check the oxygen sensor for damage

Unplug the oxygen sensor harness so that the oxygen sensor is no longer connected to the computer and the feedback control system is in open loop control. Connect the positive test lead of the multimeter voltage file directly to the oxygen sensor feedback voltage output terminal, and the negative test lead is well grounded. To measure the feedback voltage while the engine is running, first disengage the crankcase forced ventilation pipe or other vacuum hose connected to the intake pipe to artificially form an aura, while watching the voltmeter, the pointer reading should drop. Then connect the disconnected pipeline, unplug the water temperature sensor connector, replace the water temperature sensor with a 4-8KΩ resistor, artificially form a thick mixture, and watch the voltmeter, its pointer reading should rise. You can also use the method of suddenly pressing or releasing the accelerator pedal to change the concentration of the mixture. When the accelerator pedal is suddenly pressed, the mixture becomes richer and the feedback voltage should rise; when the accelerator pedal is suddenly released, the mixture becomes leaner. The feedback voltage should drop. If the feedback voltage of the oxygen sensor does not change as above, it indicates that the oxygen sensor is damaged.

In addition, when the titanium oxide type oxygen sensor is detected by the above method, if it is a good oxygen sensor, the voltage at the output terminal should fluctuate up and down around 2.5V. Otherwise, the sensor can be removed and exposed to air, and its resistance value is measured after cooling. If the resistance value is large, the sensor is good, otherwise the sensor should be replaced.

5) Check the appearance color of the oxygen sensor

Remove the oxygen sensor from the exhaust pipe and check whether the vent hole on the sensor housing is blocked or the ceramic core is damaged. If damaged, the oxygen sensor should be replaced.

The fault can also be judged by observing the color of the top part of the oxygen sensor:

â‘ Light gray top: this is the normal color of the oxygen sensor;

â‘¡White tip: caused by silicon pollution, the oxygen sensor must be replaced at this time;

â‘¢Brown tip: caused by lead pollution, if serious, the oxygen sensor must be replaced;

â‘£Black top: caused by carbon deposits, after removing the engine carbon deposits, the carbon deposits on the oxygen sensor can generally be automatically removed.

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