What Causes a Vehicle Not to Use Urea?
3 Answers
Vehicle not using urea may indicate that the SCR system is in a non-operational state. Environmental protection agencies worldwide have proposed further reductions in nitrogen oxide pollutants emitted by diesel engines. Engine manufacturers have adopted SCR technology to meet these environmental requirements. Urea is added to vehicles to treat diesel engine exhaust. Below is an introduction to urea: Function of urea: Automotive urea is used when nitrogen oxides are detected in the exhaust pipe. The urea tank automatically sprays diesel exhaust fluid, which reacts with nitrogen oxides in the SCR catalytic converter through redox reactions, producing harmless nitrogen and water vapor that are then expelled. Working principle: When nitrogen oxides are detected in the exhaust pipe, the urea tank automatically sprays diesel exhaust fluid. The fluid reacts with nitrogen oxides in the SCR catalytic converter through redox reactions, producing harmless nitrogen and water vapor that are expelled.
I've been repairing diesel vehicles for over a decade, and there are quite a few common reasons for urea not being burned. The most frequent issues are clogged urea pumps or crystallized nozzles, especially when using inferior quality urea – the nozzles can get blocked as if cemented shut. A faulty exhaust temperature sensor is another culprit; if it thinks the exhaust temperature isn't high enough, the system won't allow urea injection. Problems with the urea level sensor can make the computer mistakenly think there's no urea available, even when the tank is full. Electrical issues should also be checked – blown fuses or oxidized wiring harness connectors can cause this too. If the vehicle lacks power and emits white smoke while driving, there's a high chance the post-treatment system is triggering an alarm. You should immediately use a diagnostic tool to read the fault codes – don't force it to run, as a completely blocked catalytic converter will make your wallet hurt during repairs.
Last time I went on a long trip, I encountered this situation—the yellow urea light on the dashboard came on. It turned out the urea pump filter was completely clogged with debris. The mechanic said you should always use sealed original urea containers, as open barrels easily collect dust. Also, in winter when temperatures drop too low, the urea can freeze and the pump won’t work at all—you have to check if the heating lines are broken. The worst part is some people try to save money by reprogramming the ECU to disable the urea system, only to fail emissions tests later and have to restore the system. Honestly, the urea system is like the kidneys of the car—if it fails, toxins can’t be expelled, and the engine goes into limp mode, struggling up hills like an old ox panting. It’s really not worth it.
