What does the urea quality sensor do? Why is the urea fault light on?

What is the role of urea quality sensor

There are several situations, as follows:
1. The vehicle is weak and the urea consumption is normal
Fault phenomenon: the owner of the vehicle is weak, the urea consumption is normal, and the muffler can be found to emit a small amount of white smoke when refueling.
Failure analysis: Read the failure code with the diagnostic instrument as the engine emission exceeds the standard, and there are no other failures. Remove the urea nozzle and use the diagnostic instrument to do the injection test, and no abnormality was found. During the inspection, it was found that a large number of urea crystals in the high-temperature catalytic tube were seriously blocked, so the exhaust elbow was removed to clean it and the air belt was used to clean the soot attached to the ceramic surface of the catalytic converter. Replacement of urea solution test failure disappeared.
Fault summary: After the urea crystallization fails, a large amount of urea is accumulated in the exhaust pipe, which not only causes the engine exhaust to be blocked and weak, but also causes the emission to exceed the standard, and the OBD torque is limited after several driving cycles. The main reason is that the quality of urea is not up to standard.
2. The urea pressure is too low and the urea consumption is high
Fault phenomenon: The fault light of the instrument in the car flashes frequently, and the fault code shows that the urea pressure is too low and the urea consumption is high.
Failure analysis: The upper part of the urea tank of the car has serious leakage. The urea tank assembly and urea pump have been replaced. After the replacement, there is still a leakage of urea solution. During the inspection, it was found that the leaking position was the vent hole of the urea tank. To rule out the possibility of adding too much urea solution, check the water heating valve of the urea tank. It is found that the water heating valve is often damaged, replace the water heating valve, and troubleshoot.
Fault summary: The temperature in the urea tank is too high, causing the urea to volatilize and crystallize around the urea tank after being discharged from the vent hole. Excessive crystallization of the vent holes leads to blockage of the vent holes. When the urea system is working, the vacuum in the box is serious, and the urea pressure buildup is blocked, so the fault that the urea pressure is too low is reported.
3. Insufficient power, urea consumption is too high or too low
Fault phenomenon: The fault light is always on. Underpowered, torque is limited to 1800 rpm. The SCR system is not working properly, the urea consumption is too high or too low.
Fault analysis: Read the fault code with the diagnostic instrument: the voltage signal of the urea dosing pump pressure sensor is high, the actuator 2 is short-circuited to the ground, the urea reversing valve actuator is open, and the sensor power supply 3 is wrong. After inspection and processing of the urea dosing pump power supply module, it was found that there was a large range of corrosion, which led to the connection of the plug-in wiring harness in the power supply module, and the wrong voltage value signal was transmitted to the ECU.
Solution: replace the urea dosing pump and the plug of the power supply module. After the replacement, the urea fault code can be cleared again by detecting the urea, but only the sensor power supply 3 cannot be cleared. Analyzing the sensor power supply 3 refers to the internal power supply module of the ECU, replacing the rail pressure sensor and troubleshooting.
The urea liquid warning light is a kind of protection for the SCR system, and the urea liquid warning light usually indicates a related fault. The reasons are: the urea solution has been exhausted, the quality of the urea solution is unqualified, and the SCR system pipeline is blocked. This usually results in increased fuel consumption. Power drop. You should go to a professional service station in time to rule out the cause.
The common reasons for the post-processing SCR light to be on are: insufficient urea amount (you can check whether the urea amount is normal), nitrogen oxygen sensor failure, urea nozzle failure
Similar failures generally require professional equipment for testing. It is recommended to go to the nearest Yuchai service station for inspection and maintenance according to the list attached to the engine maintenance manual. During the three-guarantee period, Yuchai implements free maintenance.