What does the SCR fault light mean?
4 Answers
When the engine SCR fault light is on, it indicates a malfunction in the corresponding component's function. Common causes for the engine SCR fault light include: Insufficient urea level (you can check the urea level yourself), NOx sensor failure, urea injector malfunction, urea injector blockage, or urea pump fault light. Here is some relevant information: 1. For such faults, professional diagnostic equipment is required. It is recommended to refer to the maintenance manual provided with the engine and visit the nearest Yuchai service station for inspection and repair. During the warranty period, Yuchai provides free repairs. 2. Selective Catalytic Reduction (SCR) is a process designed to treat NOx emissions in diesel vehicle exhaust. It involves injecting a reducing agent, such as ammonia or urea, in the presence of a catalyst to convert NOx in the exhaust into N2 and H2O.
I usually drive heavy trucks for long-distance hauls, and the SCR light coming on is all too common. That yellow light indicates the exhaust treatment system is acting up, most likely due to insufficient urea spray or a clogged nozzle. Last time my truck's light came on, it was because urea crystallization blocked the nozzle, causing a 30% drop in power and fuel consumption to skyrocket to terrifying levels. When this happens, don't panic—the best move is to head to a service station to read the fault codes with a computer. Trying to fix it yourself can easily trigger a speed limit mode. If the dashboard shows a red light flashing along with the DPF light, stop immediately and call for rescue. Continuing to drive could burn out the urea pump, and replacing a new one could cost half a month's wages!
My diesel SUV suddenly had this urea warning light come on last time. The mechanic said there was an issue with the exhaust purification system in the tailpipe. The most common cause is when the urea fluid is running low, and the dashboard will give an early warning. Another possibility is the urea nozzle getting clogged with impurities, which affects engine power if the spray becomes uneven. Pipe crystallization is also a frequent cause of failure, especially in winter when low temperatures make urea prone to clumping. It's recommended to always keep two bottles of urea in the trunk. When the yellow light comes on, don't delay more than 200 km—just go to the repair shop for an 80-yuan computer reset. If the red light comes on, you must stop driving immediately, otherwise the vehicle will be locked to a maximum speed of 20 km/h!
The SCR system is essentially a selective catalytic reduction technology that decomposes ammonia from urea with a concentration of 32.5%, converting nitrogen oxides into harmless nitrogen and water in the catalytic converter. The illumination of the fault light usually indicates abnormalities in several key components: a deviation of more than 10% in the urea tank level sensor, pressure fluctuations greater than 0.2MPa in the dosing pump, or incorrect urea injection timing due to a faulty exhaust temperature sensor. A hidden fault point is NOx sensor poisoning, especially when using urea from small manufacturers for a long time, which can lead to catalyst poisoning. Replacing the sensor can cost three to four thousand.
