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When The Urea Nozzle Was Removed, The Coolant Lamp Turned On. This Is The Original Problem

Two days ago, a card friend consulted in the evening that his liberation J6 sometimes limited the power of the engine due to the blockage of the urea nozzle. He removed the urea injection unit and cleaned it up. As a result, he found that the alarm light for insufficient coolant level was on. So why?

First of all, after the medium and heavy truck entered the era of national four emission, Basically, most models adopt selective catalytic reduction (SCR) technology to meet the emission standard. The most obvious feature of SCR technology is the consumption of urea solution. The currently used vehicle urea solution is generally composed of 32.5% high-purity urea and 67.5% deionized water to reduce nitrogen oxides. Vehicle urea solution was first used in Europe, called AdBlue and def in North America (diesel exhaust fluid, i.e. diesel engine exhaust treatment fluid), which is called vehicle urea solution or “vehicle denitration agent” in China.

Due to the characteristics of urea solution, it means that when the temperature is low in winter, the urea solution is easy to crystallize or freeze. Once crystallized, it is easy to lead to the blockage of urea injection unit, resulting in the failure of SCR post-treatment system, and the power and torque output of the vehicle is limited. Therefore, generally, the vehicle SCR system is equipped with a heating system. The common heating methods generally use electric heating and coolant heating.

At present, SCR post-treatment system heated by coolant is relatively common. It may be known that there is a water heating system in the urea tank. When the temperature of the urea tank is lower than a certain temperature, When the coolant is higher than a certain temperature (e.g. 55 ℃), ECU opens the solenoid valve, and the hot coolant flows into the heating water pipe on the urea level and temperature sensor to heat the urea tank. The urea temperature sensor measures the urea temperature in the urea tank to control the starting and heating time of urea heating and thawing.

Three Line Connections On The Urea Injection Unit

Structure Diagram Of Urea Injection Unit

However, it should be noted that the urea injection unit is also connected with two coolant water pipes. Urea injection unit is commonly known as urea nozzle. Its main body is a solenoid valve, which is controlled by DCU to realize urea injection; The surrounding is a cooling water channel leading to the expansion tank, which is mainly used to cool the solenoid valve; The upper end is urea inlet. Therefore, after removing the urea injection unit, kayou actually disconnected two coolant water pipes, and the position of the urea injection unit is generally lower than that of the expansion water tank, resulting in the loss of coolant, which leads to the insufficient coolant alarm light, which can be supplemented with coolant.

Postscript:

With the full implementation of the national four regulations and the promotion of the Yellow standard vehicle policy, more and more users will begin to use the national four medium heavy truck products with SCR system. In addition, the weather in the north is getting colder, the SCR system also needs to attract enough attention and conduct more preventive inspections.

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