We know that every electronic fuel injection vehicle has two oxygen sensors to ensure that the fuel can be fully burned and the emission meets the standard. The front oxygen sensor in front of the three-way catalytic converter is used to detect the oxygen content in the exhaust gas and feedback to the ECU to correct the injection amount to maintain the appropriate air-fuel ratio; and the one behind the three-way catalytic converter is called the rear oxygen sensor, which cooperates with the front oxygen sensor to detect whether the three-way catalytic converter is working properly. If the oxygen sensor is damaged, the engine fault light will generally light up. If it is broken, it needs to be replaced and cannot be repaired.
However, if the oxygen sensor fails due to carbon deposit pollution, causing the sensor sensitivity to decrease, it can be solved by cleaning. The oxygen sensor is not inside the engine, does not contact the engine oil, and does not contact the gasoline, so why is it still polluted by carbon deposits? That is because there will be granular carbon deposits in the exhaust gas passing through the exhaust pipe. The oxygen sensor is inserted in the exhaust pipe and will directly contact the particulate matter in the exhaust gas. This is why the three-way catalytic converter is blocked. Long-term accumulation will also cause the oxygen sensor to be polluted.
When the following four fault phenomena occur in the car, after generally eliminating other faults, you can consider cleaning the oxygen sensor:
1. Increased fuel consumption, because carbon deposits in the oxygen sensor will cause its signal output to be abnormal, resulting in an imbalance in the engine mixture ratio, which will increase fuel consumption; 2. Increased emission of pollutants, one of the annual exhaust emission tests cannot meet the standard, making the annual inspection unqualified. In fact, this is also easy to understand, because although the three-way catalyst can purify the exhaust gas, its purification capacity is limited. Once the oxygen sensor works abnormally, it will cause incomplete engine combustion and increase the emission of pollutants, even if the three-way catalytic converter works normally. Therefore, if the annual exhaust gas of the old car does not meet the standard, in addition to cleaning the three-way catalyst, you should also consider cleaning or replacing the oxygen sensor; 3. There is a possibility of black smoke, which is caused by the abnormal operation of the oxygen sensor and the abnormal air-fuel ratio; 4. The engine speed is unstable and shaking, which is also caused by the abnormal air-fuel ratio.
If the oxygen sensor is damaged or the heater fails (the heating sensitive element is damaged), it must be replaced; if it is only because the oxygen sensor is polluted by carbon deposits and the sensitivity is reduced, the problem can be solved by cleaning. Carbon deposits have always been a stubborn problem in cars and are difficult to avoid, especially in older cars. Carbon deposits on the throttle, the back of the intake valve, the fuel injector, etc. will directly affect the performance of the engine. Over time, the carbon deposits will mix into sludge, which can easily cause damage to the cylinder wall, air leakage, and serious reduction in power performance. In fact, carbon deposits are difficult to avoid, but we can pay more attention to them in normal driving, such as minimizing idling time, avoiding long-term stop-and-go, and often driving on the highway. The most important thing is to clean the carbon deposits when the engine performance decreases. Cleaning is also the only effective way to solve carbon deposits.
In addition to the carbon deposits generated inside the engine, the engine also has insufficient combustion, which increases the solid particulate matter in the exhaust. These particulate matter (carbon deposits) will accumulate on the oxygen sensor and the three-way catalytic converter through the exhaust pipe, causing the oxygen sensor to be poisoned and the three-way catalytic converter to be blocked. This oxygen sensor poisoned by carbon deposits can be reactivated by cleaning, which is why it is only carbon deposit pollution and does not need to be replaced. There are many ways to clean the oxygen sensor. Similar to the cleaning of the three-way catalyst by soaking it in oxalic acid solution, the oxygen sensor can also be cleaned by soaking it in oxalic acid solution or ferric chloride solution mixed with an appropriate amount of hydrochloric acid.