Common Faults of NOx Sensors and How to Diagnose Them Quickly
Apr 09,2026
NOx sensors are key components of diesel engine exhaust aftertreatment systems, responsible for monitoring the concentration of nitrogen oxides in the exhaust gas and ensuring that the vehicle meets emission standards. However, due to the harsh working environment (high temperature, corrosion), NOx sensors are prone to failures, which often cause the engine fault light to turn on, emission failures, and even engine power reduction. For mechanics and auto parts purchasers, being able to quickly diagnose and solve NOx sensor faults is crucial to improving maintenance efficiency and reducing costs.
The first common fault is sensor drift, which is mainly caused by long-term use or exposure to high-temperature exhaust gas. The performance of the sensor degrades, resulting in inaccurate data transmission, and the ECU cannot correctly control the urea injection amount, leading to emission failures. This fault can be diagnosed using OBD diagnostic equipment—if the fault code shows "NOx sensor signal abnormal", it is likely that sensor drift has occurred, and the sensor needs to be replaced in time. The second fault is sensor short circuit or open circuit, which is caused by damaged wiring harness or sensor internal failure. At this time, the sensor will not output any signal, and the engine will enter a fault protection mode, reducing power. The solution is to check the wiring harness for damage and replace the faulty sensor if necessary.
The third fault is sensor contamination, which is caused by urea crystallization or exhaust impurities adhering to the sensor probe, affecting the sensor’s detection accuracy. This fault is often accompanied by unstable urea injection and increased emissions. The solution is to clean the sensor probe with a professional cleaning agent, and if the contamination is severe, replace the sensor. Our NOx sensors are manufactured with high-temperature resistant and corrosion-resistant materials, with a low failure rate and high detection accuracy, compatible with Bosch, Denso, and other OEM standards. We also provide professional technical guidance to help you quickly diagnose and solve NOx sensor faults, ensuring the normal operation of the exhaust aftertreatment system.
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5F, Nanchen Building, No. 112, Liuqiao, Nanyuan East Road, Xialin Street, Chengxiang District,Putian City,Fujian Province