Maintaining an SCR (Selective Catalytic Reduction) Urea pump (a core component of diesel vehicle after-treatment systems, responsible for accurately injecting urea solution into the exhaust to reduce NOₓ emissions) is critical to ensuring its performance, extending its service life, and avoiding costly repairs. Below is a detailed, step-by-step guide to daily and regular maintenance for SCR Urea pumps:
Daily checks focus on "visual inspection" and "basic function verification" to quickly identify obvious abnormalities. Perform these checks before starting the vehicle or after daily use:
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Urea Solution Level & Quality Check
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Level: Check the urea tank gauge (or electronic display) to ensure the urea solution level is above the "minimum mark" (never let it run empty). Running out of urea will trigger the vehicle’s fault code, limit power, and damage the pump (due to dry operation).
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Quality: Use a transparent container to take a small amount of urea solution— it should be colorless, transparent, and free of sediment or turbidity.
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Never use inferior urea (e.g., low-purity, diluted, or adulterated products), as impurities (such as metal ions, dust, or organic matter) will clog the pump’s filter, nozzle, and internal valves, leading to irreversible wear.
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Must use ADBlue® (ISO 22241 standard urea solution) (32.5% high-purity urea + 67.5% deionized water)—this is the only specification compatible with SCR systems.
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Urea Tank & Filler Neck Inspection
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Check the tank for cracks, leaks, or damage (especially at the connection to the pump). Even small leaks can cause urea loss and moisture intrusion (which dilutes the solution).
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Clean the filler neck and cap seal: Remove dust, debris, or dried urea residue with a clean, lint-free cloth. A damaged or dirty seal will allow contaminants to enter the tank, risking pump clogging.
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Ensure the cap is tightly closed after refueling—loose caps lead to solution evaporation and contamination.
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Pump & Pipeline Visual Check
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Inspect the urea pump (usually mounted near the tank or exhaust) for oil stains, urea leaks, or loose bolts. Leaks at the pump’s inlet/outlet hoses indicate worn seals or loose clamps, which need immediate replacement/tightening.
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Check the urea injection line (connecting the pump to the exhaust nozzle) for kinks, cracks, or rodent damage. Kinked lines restrict flow, causing the pump to work under overload; cracked lines lead to urea leakage and inaccurate injection.
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Fault Code & Warning Light Check
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Turn on the vehicle’s ignition (without starting the engine) and check the instrument panel for SCR-related warning lights (e.g., "Urea Low," "SCR Fault," or "Pump Malfunction") or fault codes.
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If a warning light illuminates, do not ignore it—use a professional diagnostic tool (e.g., OBD scanner for commercial vehicles) to read the code and address the issue (e.g., refill urea, clean filters) immediately. Delayed repairs can lead to pump burnout or SCR catalyst damage.
In addition to daily checks, perform scheduled maintenance based on the vehicle manufacturer’s recommendations (typically every 10,000–30,000 km, or 6–12 months—refer to the owner’s manual for exact intervals):
The SCR urea pump has two key filters to prevent contamination—must be replaced on schedule:
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Urea Tank Filter (Suction Filter): Installed at the bottom of the urea tank (connected to the pump’s suction line), it filters large impurities (e.g., sediment, debris) from the solution.
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Replacement Steps:
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Empty the remaining urea solution from the tank (or use a siphon to pump it out) to avoid spillage.
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Disconnect the suction line from the tank, remove the old filter (twist counterclockwise), and clean the filter seat with deionized water (never use tap water—contains minerals that clog the pump).
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Install a new, OEM (original equipment manufacturer) filter (use only manufacturer-approved parts—generic filters may not fit or filter effectively).
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Reconnect the line, refill with standard urea solution, and start the vehicle to check for leaks.
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Urea Pump Internal Filter (Pressure Filter): Located inside the pump, it filters fine impurities (e.g., tiny particles, degraded urea crystals) to protect the pump’s internal valves and pistons.
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Note: This filter is usually replaced by a professional technician during pump servicing (it requires disassembling the pump, which is not a DIY task). Do not attempt to open the pump yourself—incorrect disassembly will damage internal components.
Over time, urea solution may crystallize (due to temperature changes or incomplete injection) inside the pump and nozzle, causing clogging and inaccurate flow:
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Professional Cleaning (Recommended):
Use a dedicated SCR urea system cleaning machine (available at commercial vehicle repair shops) to flush the pump, lines, and nozzle with specialized urea system cleaner (not tap water or harsh chemicals). The cleaner dissolves crystals without corroding the pump’s plastic/metal components.
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Avoid DIY Flushing: Never use tap water, diesel, or gasoline to clean the system—tap water contains minerals that form scale; petroleum-based fluids damage the pump’s seals and corrode internal parts.
The injector (mounted on the exhaust pipe) sprays urea into the exhaust stream—clogged injectors cause uneven injection, reducing SCR efficiency and overloading the pump:
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Inspection: Use a diagnostic tool to test the injector’s spray pattern (should be a fine, uniform mist). If the spray is uneven, dripping, or absent, the injector needs cleaning or replacement.
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Cleaning: A technician will remove the injector, soak it in urea system cleaner (for 30–60 minutes), and use compressed air (low pressure, 2–3 bar) to blow out residual crystals. Replace the injector if cleaning fails to restore performance.
Use a professional SCR diagnostic tool to test the pump’s key parameters—this ensures it meets the system’s requirements:
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Pressure Test: The pump should build pressure to the manufacturer’s specified range (typically 5–10 bar) within 10–30 seconds after startup. Low pressure indicates a clogged filter, leaky line, or worn pump piston; high pressure suggests a blocked injector or faulty pressure relief valve.
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