Guidelines for Diagnosing and Preventing Crystallization Blockages in Selective Catalytic Reduction Urea Nozzles

Problem Overview
The selective catalytic reduction system uses urea solution to reduce nitrogen oxides in exhaust gases. Nozzle crystallization and blockage can lead to uneven or interrupted urea injection, resulting in emissions control failures, fault light alerts, regeneration failures, or even the inability to start the vehicle, causing significant inconvenience for vehicle owners.

Main Causes

1. If the urea quality is substandard or contaminated with water, impurities can easily crystallize and precipitate.
2. When a vehicle is parked for an extended period or left unused for a long time, the urea in the nozzles and pipelines will evaporate and crystallize.
3. Low-temperature environments cause freezing, leading to crystallization or solidification of crystals at the nozzle outlet.
4. A malfunction in the nozzle heater, temperature sensor, or injection pump can lead to insufficient heating or abnormal injection.
5. Filter blockage or residual material in the pipeline can lead to localized concentration increases and subsequent crystal formation.

Typical Symptoms and Identification

• The instrument or diagnostic tool displays emission control-related fault codes and a malfunction indicator light.
• Abnormal urea solution consumption or abnormal liquid level indication.
• After startup, the exhaust emits a pungent ammonia odor or white smoke; engine power decreases or idle speed becomes unstable.
• After a vehicle has been parked for an extended period, white or pale yellow crystalline deposits can be seen at the nozzle.
• The diagnostic data indicate abnormal injection pressure, insufficient heating power, or low injection volume.

Key Points for Examination and Diagnosis

• First, read the fault codes to determine whether the issue is related to the urea injection or heating system.
• Visually inspect the nozzle and external piping for any crystallization, taking care not to strike them forcefully.
• Check the urea tank, filter, pump pressure, and heater operation.
• Under professional conditions, the nozzle can be removed for test spraying or ultrasonic cleaning, and the atomization performance of the spray can be inspected.
• During the warranty period, please contact an authorized service center first to avoid voiding your warranty by attempting to disassemble the device yourself.

Cleaning and Maintenance Methods

• For minor crystallization, you can try using a specialized cleaning agent and heating device at a professional repair shop to soften and flush it out.
• For severe blockages, it is recommended to replace the nozzle or related pipeline components, and also to replace the filter.
• If the nozzle and catheter become clogged repeatedly, you should inspect and repair any faults in the heating system or the electronic control unit.
• Avoid using household solvents or strong acids and bases for cleaning, as they may damage the nozzle’s precision structure.
• When replacing parts, prioritize using original manufacturer parts or high‑quality, reliable accessories to ensure compatibility and durability.

Preventive Measures and Daily Maintenance

• Use qualified, brand‑reliable urea solution and avoid refueling with liquids that are damp or contaminated.
• Follow the manufacturer’s maintenance manual, regularly replace the urea system filter element, and inspect the heating device.
• In winter, take precautions against freezing; try to start and drive the vehicle for short periods in low temperatures, and avoid leaving it parked idle for extended periods.
• Before parking, try to activate the urea system heater or park in a warm environment to minimize the crystallization of residual fluid in the pipelines.
• Regularly take your vehicle to a professional repair shop for system calibration and injector inspection, especially if it has high mileage.

Fees and Processing Recommendations
Repair costs vary significantly depending on the severity of the malfunction and the type of parts used. Simple cleaning is relatively inexpensive, while replacing nozzles or modules in severe cases can be quite costly. During the warranty period, it’s best to have repairs handled at an authorized service center. After the warranty expires, you can compare quotes from several reputable repair shops and inquire about the source of the replacement parts.

Owner’s Practical Checklist

• Information on reliable channels for purchasing qualified urea.
• Check the instrument fault alerts regularly and diagnose them promptly.
• In winter, take precautions against freezing and keep the system running after frequent short starts and stops.
• If external crystallization is detected, take photos immediately and have it inspected at a professional repair shop.

Recommendation
When urea nozzle crystallization and blockage occur, avoid forcibly disassembling or aggressively attempting to fix the issue yourself. First, diagnose the root cause of the failure; for minor issues, a simple cleaning may suffice. In cases of severe or recurring failures, replace the damaged components and thoroughly investigate the underlying system causes. Regular maintenance and the use of qualified urea solution are the most cost‑effective and efficient preventive measures.