Ad-blue Injector

AdBlue injectors dose a urea solution into the exhaust gas stream upstream of the SCR catalyst (Selective Catalytic Reduction). A correct spray pattern and accurate dosing rate are essential to reduce nitrogen oxides without excessive deposits or ammonia slip. When faults occur in MAN and Mercedes trucks, buses and vans, diagnosis must therefore go beyond the injector alone: supply pressure, fluid quality, exhaust gas temperature and control signals all influence the result.

AdBlue dosing modules regulate the amount of AdBlue delivered into the exhaust gas stream through the injector. Depending on the system configuration, the dosing valve is mounted separately from the spray nozzle or combined with the injector in a single module. The interaction between the pump, dosing module and injector determines whether the required amount of AdBlue is delivered accurately.

Always identify parts using the vehicle's chassis number. Visual comparison or selection based solely on the model name is never sufficient. For example, dosing modules for MAN TGS and TGX with D20 or D26 engines and Mercedes Actros with OM 471 vary according to emissions class, year of manufacture and aftertreatment system. The specific system configuration must also be checked for Lion’s City, Citaro, TGE and Sprinter.

There are air-assisted dosing systems and airless versions, in which fluid pressure provides atomisation. Check whether the application requires a separate nozzle or a complete dosing module with an electrically operated dosing valve. Operating pressure, flow characteristics, spray angle, connector pinout, installation depth and flange fit must match. Some airless systems operate at around 5 bar, while others use higher pressures; only the vehicle-specific test values should be used as the reference. Corrosion-resistant metals, such as suitable grades of stainless steel, and urea-resistant seals prevent material degradation. Any coolant connections and heat shields must also be considered when selecting the part.

The Emitec Air-Assisted Dosing Module is connected to the Emitec pump. This injector has two inlets: one for AdBlue and one for compressed air. The compressed air disperses the AdBlue into a fine mist in the exhaust pipe. In this air-assisted version, a correct compressed air supply is required alongside the AdBlue supply to achieve the correct spray pattern.

The Bosch Denoxtronic 2.2 Dosing Module is an airless solenoid valve. Atomisation takes place without compressed air: the fluid pressure generated by the pump forces the AdBlue through a microscopically small spray nozzle. The dosing valve controls the quantity injected.

On the Hilite / BlueTec Nozzle, the electronic dosing valve is often mounted close to the pump. This valve regulates the amount of AdBlue supplied to the injector. The actual injector on the exhaust pipe is a mechanical, heat-resistant spray nozzle. The dosing valve and spray nozzle are therefore separate components in this configuration.

The Bosch Denoxtronic 2.2 / Euro 6 Dosing Valve is a compact solenoid injector bolted directly onto the exhaust aftertreatment system, the large silencer/catalyst unit. On Mercedes Euro 6 trucks, this module is often water-cooled through the engine cooling system to protect the electronics from overheating.

White crystals around connections often indicate external leakage. Deposits on the spray nozzle or mixing pipe can result from after-dripping, insufficient atomisation or prolonged operation at low exhaust gas temperatures. Other faults include open circuits in the solenoid coil, corroded connectors and thermal damage. Emissions warnings, power derating or restart restrictions do not, on their own, prove that the injector is faulty.

1. Read out fault codes and stored operating conditions. Compare the commanded dosing quantity, measured supply pressure, exhaust gas temperatures and readings from the NOx sensors (nitrogen oxide sensors) upstream and downstream of the catalyst under suitable test conditions.
2. Check the fluid using a refractometer suitable for AdBlue: the nominal urea concentration is 32.5% by mass. Inspect supply lines, the filter and connections for contamination, crystals and leaks.
3. Use diagnostic equipment to carry out pressure build-up and pressure retention tests. If necessary, verify abnormal sensor readings with a suitable pressure gauge in accordance with the manufacturer's procedure. Distinguish pump faults and supply blockages from leakage through the dosing valve.
4. Measure the supply voltage and wiring continuity in accordance with the wiring diagram. Where specified, check the coil resistance at a known temperature; assess the electrical control signal with an oscilloscope if necessary. Do not apply battery voltage directly unless specified.
5. Carry out the specified dosing quantity test with the injector removed and placed in a suitable collection setup. Weigh the fluid collected over the specified test period and compare the mass, spray pattern and after-dripping against the manufacturer's tolerances.

Allow the exhaust to cool, wear gloves and eye protection, and depressurise the dosing circuit in accordance with the workshop procedure. Remove accessible crystal deposits only using an approved method, generally with warm demineralised water where permitted. Never insert sharp objects into the spray holes: damage alters the calibrated orifice and droplet formation. Replace modules with electrical faults, damaged seats or persistently out-of-specification test results.

Check the mixing pipe, mounting seat, heat shields and any cooling provisions. Fit the specified new seals and observe the tightening torque and spray direction. Also repair faulty heating or purge functions where fitted. Then carry out the specified commissioning procedure, leak check and dosing test. Confirm during a controlled road test that emissions readings return to normal; simply clearing fault codes will not prevent recurring downtime.

Braem has all the test equipment required to recondition and test AdBlue dosing modules in its own workshop. These reconditioned AdBlue dosing modules are available on an exchange basis with warranty.