Ad-blue pump

The AdBlue pump delivers the urea solution from the tank to the SCR (Selective Catalytic Reduction) system’s dosing unit at a controlled pressure. Insufficient flow, unstable pressure or failure to build pressure disrupt dosing and can cause emissions faults, torque limitation or a pending restart lockout. On MAN and Mercedes trucks, buses and vans, however, a pressure fault does not automatically indicate a defective pump: suction problems, blocked filters and leaking dosing injectors can cause similar symptoms.

Always identify parts using the vehicle’s chassis number. Visual comparison or selection based solely on the model name is never sufficient. For example, on MAN TGS and TGX models with D20 or D26 engines and Mercedes Actros models with OM 471 engines, the emissions class, production date and exhaust aftertreatment configuration also determine which supply module fits. MAN TGE, Mercedes Sprinter and buses such as Lion’s City and Citaro also have version-specific connections and control systems.

There are standalone electric pumps and integrated supply modules with a filter, pressure sensor, heater and suck-back function. Air-assisted and airless dosing systems have different requirements for pressure regulation and connections. Check the supply voltage, for example 12 or 24 volts, connector pinout, line couplings, return circuit configuration and software compatibility. Some systems operate at around 5 bar, others at around 9 bar; use only the specified operating pressure, pressure build-up time and permissible pressure deviation for the version concerned.

AdBlue contains 32.5% urea by mass and must comply with ISO 22241, the standard for this urea solution. Components in contact with the fluid require compatible plastics, stainless steel and suitable seals; copper-containing materials can contaminate the fluid. AdBlue freezes at around −11 °C. A faulty heater or incomplete thawing can therefore temporarily cause the same symptoms as pump damage.

1. Bosch Denoxtronic 1.1: This pump type was widely used on Euro 4 and early Euro 5 models. It is a mechanical/electric pump that works with the truck’s compressed air system to move the fluid.
2. Bosch Denoxtronic 2.2 (Airless): Introduced on later Euro 6 models. This pump type no longer requires compressed air; it is a dedicated high-pressure plunger pump (operating at approximately 5 bar fluid pressure) with fully electronic control of AdBlue delivery.
3. Emitec UDA (including Type Gen2 / UDA26146): This is the well-known, robust square metal module. This pump is widely used on Euro 5 and Euro 6 engines. It operates with an internal diaphragm and uses compressed air both to transport and atomise the fluid.

1. Hilite / Cummins EcoFit: This pump type is the standard fitment on the Euro 5 Actros (MP2/MP3) and early Euro 6 models. It is a heavy-duty module fitted with cooling fins. This air-assisted system uses the truck’s compressor to maintain AdBlue pressure.
2. Bosch Denoxtronic 2.2 (Mercedes Euro 6 Type): Used on more recent Euro 6 models (Actros MP4/MP5, Antos). This is a fully electronic, compact pump with a single electrical connector that operates without compressed air assistance (airless).

1. Bosch Denoxtronic 5 / 5.x (Tank Module): This pump type is fully integrated into a plastic module screwed into the bottom of the AdBlue tank. It is found in the MAN TGE as well as the Mercedes Sprinter and Vito. The pump delivers a constant fluid pressure of up to 6 bar.
2. Bosch Airless Dosing Module (Vans): A very compact, standalone injector secured with a simple band clamp in the front exhaust pipe (downpipe), controlled directly by the engine ECU.

1. Read out fault codes and operating data. Record the conditions under which the fault occurred, tank temperature, target and measured supply pressure, and pump control signals. Check that the conditions required to enable pressure build-up are met.
2. Check the fluid and suction path. Measure the urea concentration using a suitable, calibrated refractometer. Inspect the tank pick-up, filters and lines for contamination, kinks and air ingress. White crystal deposits around couplings often indicate leaks.
3. Measure the electrical supply under load. Use a multimeter to check the supply voltage and voltage drop across the power and earth connections during an actuator test. Measure the current draw with a current clamp and compare it with the manufacturer’s specifications; assess any deviations in conjunction with the hydraulic load.
4. Test pressure build-up and pressure retention. If necessary, compare diagnostic readings with an AdBlue-compatible pressure gauge connected via the specified test adapter. Measure the build-up time and pressure behaviour according to the test programme. Rule out leakage through the dosing injector, return circuit or internal control components before condemning the pump.
5. Check delivery volume and the shutdown cycle. Perform the specified dosing quantity test using a measuring cylinder or scales. On systems equipped with this function, also check suck-back after shutdown; residual fluid increases the risk of crystal formation and frost damage.

First allow the specified shutdown cycle to complete, then depressurise the circuit according to the manufacturer’s procedure. Use clean tools and equipment reserved exclusively for AdBlue. Eliminate contamination and suction restrictions before installation; otherwise, the replacement pump will also be damaged. Replace the specified filters and seals, check that quick-release couplings are correctly seated and observe the tightening torques. Do not use general-purpose lubricants on seals.

After installation, carry out the specified filling, bleeding and, where applicable, adaptation procedure. Confirm that the root cause has been eliminated by performing a pressure test, a dosing test and a leak check. Simply clearing fault codes will not correct insufficient supply pressure.

Braem has all the testing equipment needed to sell AdBlue pumps reconditioned in its own workshop on an exchange basis with a warranty.