Oxygen sensors are essential components in the use of ternary catalytic converters to reduce exhaust pollution. Since the air-fuel ratio of the mixed gas deviates from the theoretical air-fuel ratio, the purifying capacity of the three-way catalyst to CO, HC and NOX will drop sharply. Therefore, an oxygen sensor is installed in the exhaust pipe to detect the oxygen concentration in the exhaust gas, ECU sends a feedback signal, and then by the ECU control fuel injector increase or decrease the amount of fuel mixture to control the air-fuel ratio near the theoretical value.
At present, the actual application of oxygen sensors are zirconia oxygen sensor and titanium oxide oxygen sensor two. And the common oxygen sensor and a single lead, double lead and three lead points, single lead for the zirconia oxygen sensor; double lead for the titanium oxide oxygen sensor; three lead for the heating type zirconia oxygen sensor, In principle, three kinds of lead wire oxygen sensor can not be used instead.
Once the oxygen sensor failure, will make the electronic fuel injection system of the computer can not get the oxygen concentration of the exhaust pipe information, and therefore can not be on the air-fuel ratio feedback control, will make the engine fuel consumption and exhaust pollution increases, the engine idling instability, Lack of fire, surge and other symptoms. Therefore, the failure or replacement must be eliminated in a timely manner.
First, the common fault of oxygen sensors
1, oxygen sensor poisoning
Oxygen sensor poisoning is often a difficult and difficult to control a failure, especially in the often use of leaded gasoline cars, even the new oxygen sensor, can only work thousands of kilometers. If only a slight lead poisoning, then use a box of lead-free gasoline, you can eliminate the oxygen sensor surface lead, to return to normal work. But often due to the high exhaust temperature, leaving the lead into its internal, hinder the proliferation of oxygen ions, so that the oxygen sensor failure, then only replacement.
In addition, oxygen sensor silicon poisoning is also common. In general, the silicon dioxide and silicone rubber gaskets produced by the combustion of silicon compounds contained in gasoline and lubricants use improperly emitting silicone gases that will render the oxygen sensor ineffective, thus using good quality fuel and lubricants The Repair and use the right to choose and install the rubber washer, do not apply the sensor on the use of the manufacturer outside the provisions of the use of solvents and anti-sticking agent.
2, carbon deposition
Due to the engine combustion is not good, the formation of carbon in the oxygen sensor surface, or oxygen sensor into the oil or dust and other deposits into the internal, will hinder or block the external air into the oxygen sensor inside the oxygen sensor output signal inaccurate, ECU can not be timely To correct the air-fuel ratio. Resulting in carbon deposition, mainly for the fuel consumption increased, significantly increased the concentration of emissions. At this point, if the sediment is cleared, it will return to normal work.
3, oxygen sensor ceramic fragmentation
Oxygen sensor ceramic hard and brittle, with a hard object percussion or with a strong air purge, may make it fragmentation and failure. Therefore, the treatment should be particularly careful to find the problem in time to replace.
4, the heater resistance wire blown
For the heating type oxygen sensor, if the heater resistance wire ablation, it is difficult to make the sensor to the normal working temperature and lose its role.
5. The internal line of the oxygen sensor is disconnected.
Second, the oxygen sensor inspection methods
1, oxygen sensor heater resistance check
Unplug the oxygen sensor harness connector, with a multimeter resistance file measuring oxygen sensor terminal in the heater and the grounding column between the resistance, the resistance of 4-40Ω (refer to the specific model manual). If you do not meet the standards, should replace the oxygen sensor.
2, oxygen sensor feedback voltage measurement
When measuring the feedback voltage of the oxygen sensor, pull out the wiring harness of the oxygen sensor, and draw a thin wire from the feedback voltage output terminal of the oxygen sensor, and then insert the harness connector. When the engine is running, (Some models can also be measured by the fault detection socket oxygen sensor feedback voltage, such as Toyota Motor Co., Ltd. series of cars can be from the fault detection socket within the OX1 or OX2 terminal directly measured oxygen sensor Of the feedback voltage).
When detecting the feedback voltage of the oxygen sensor, it is preferable to use a pointer type multimeter with a low range (usually 2V) and a high impedance (internal resistance greater than 10MΩ). Specific detection methods are as follows:
1): the engine hot car to the normal operating temperature (or start to 2500r / min speed running 2min);
2): the negative voltage of the multimeter voltage meter connected to the fault detection socket E1 or battery negative, the table is connected to the fault detection socket OX1 or OX2 jack, or oxygen sensor harness connector on the number |
3): Let the engine to 2500r / min or so to maintain the speed of operation, while checking the voltmeter pointer can swing back and forth between 0-1V, note the 10s within the voltage meter pointer swing the number of times. Under normal circumstances, with the feedback control of the progress, the oxygen sensor feedback voltage will be 0.45V up and down constantly changing, 10s within the feedback voltage changes should be no less than 8 times. If less than 8 times, then the oxygen sensor or feedback control system is not working properly, the reason may be oxygen sensor surface carbon deposition, the sensitivity caused by lower. In this regard, the engine should be allowed to run at 2500r / min speed of about 2min, to clear the oxygen sensor surface carbon deposition, and then check the feedback voltage. If after the removal of carbon deposition can be after the voltmeter pointer changes are still slow, then the oxygen sensor damage, or computer feedback control circuit is faulty.
3, check the oxygen sensor for damage
Unplug the oxygen sensor harness connector, so that the oxygen sensor is no longer connected with the computer, the feedback control system in the open-loop control state. Will be a multimeter voltage table is directly connected with the oxygen sensor feedback voltage output terminal connection, a good negative table pen. In the engine operation to measure the feedback voltage, first off the inlet tube in the crankcase forced ventilation pipe or other vacuum hose, artificially form a lean mixture, while watching the voltmeter, the pointer reading should be reduced. And then connected to the disengagement of the pipeline, and then unplug the water temperature sensor connector, with a 4-8KΩ resistor instead of water temperature sensor, artificially form a thick mixture, while watching the voltmeter, the pointer reading should rise. It can also be used to suddenly depress or release the accelerator pedal to change the concentration of the mixture, in the sudden step on the accelerator pedal, the mixture becomes thicker, the feedback voltage should rise; suddenly release the accelerator pedal, the mixture becomes thinner, The feedback voltage should drop. If the feedback voltage of the oxygen sensor does not change as described above, it indicates that the oxygen sensor is damaged.
In addition, the titanium oxide oxygen sensor in the use of the above method of detection, if a good oxygen sensor, the output voltage should be 2.5V as the center up and down fluctuations. Otherwise the sensor can be removed and exposed to air, after cooling to measure its resistance value. If the resistance value is large, indicating that the sensor is good, otherwise the sensor should be replaced.
4, oxygen sensor appearance color inspection
Remove the oxygen sensor from the exhaust pipe, check the sensor housing on the ventilation holes are blocked, ceramic core with or without damage. If damaged, replace the oxygen sensor. By observing the color of the top part of the oxygen sensor can also determine the fault:
① light gray top: This is the normal color of the oxygen sensor;
② white top: caused by silicon pollution, this time must be replaced with oxygen sensor;
③ brown top: caused by lead pollution, if serious, must also replace the oxygen sensor;
④ black top: caused by carbon deposition, in the exclusion of engine carbon deposition failure, the general can automatically remove the oxygen sensor on the carbon deposition.