Ad-blue reservoir

AdBlue tanks and filler caps protect the urea solution against dirt, moisture ingress and leakage. They store the fluid for SCR (Selective Catalytic Reduction), but are not subject to the dosing pressure generated by the AdBlue pump. A damaged filler neck, incorrect filler cap or blocked tank vent can disrupt the fluid supply. On MAN and Mercedes trucks, buses and vans, targeted checks prevent unnecessary tank replacement when the cause lies with a seal, vent line or tank module.

Always identify tanks and caps using the vehicle's chassis number. Visual comparison or selection based on the model name alone is never sufficient. On MAN TGS and TGX models with D26 engines or Mercedes Actros models with OM 471, for example, tank capacity, mounting position and connections vary according to chassis configuration and emissions generation. The specification and available installation space must also be checked individually on Lion’s City, Citaro, TGE and Sprinter models.

Distinguish between bare tank bodies supplied separately and complete tanks with a tank module, level sensing, temperature sensors and heating. Check whether these components are included or need to be transferred from the old tank. Compare nominal capacity, fill volume, mounting distances, filler neck orientation, flange fit and connections for suction, return and coolant heating where fitted. For caps, the thread or bayonet fitting, sealing diameter, locking mechanism and specified venting arrangement are critical.

Tanks are often made of HDPE (high-density polyethylene); seals and metal fittings must be verified as AdBlue-compatible. Copper, brass and uncoated carbon steel are unsuitable for contact with the fluid. Use AdBlue with 32.5% urea by mass in accordance with ISO (International Organization for Standardization) 22241. As this solution freezes at around -11 °C and expands in the process, expansion space must be maintained and the maximum fill level must not be exceeded.

White crystals around the cap may indicate spilled fluid, but can also point to a leaking sealing ring or a deformed filler neck. Chafing beneath retaining straps, cracks at mounting points and leaks around the module flange call for checks of the rubber mounts and mounting stresses. Difficulty filling or tank deformation may be caused by blocked venting. An incorrect level reading does not, on its own, prove that the tank is faulty.

1. Read fault codes and live data for tank level, fluid temperature and heating using suitable diagnostic equipment. Compare the temperature with the ambient temperature after the vehicle has been stationary for an extended period, and assess the level against a known fill quantity.
2. Clean external crystal deposits with water, dry the surface and check again for leaks. Inspect tank seams, the filler neck, sealing rings and the module flange under good lighting.
3. Check the cap closure and vent routing in accordance with the vehicle documentation. Only carry out the specified leak test; never pressurise the tank with compressed air without following the prescribed procedure.
4. If contamination is suspected, take a sample using clean, suitable equipment. Measure the urea concentration using a calibrated AdBlue refractometer with temperature compensation. A correct concentration does not rule out contamination with diesel or dissolved metals.
5. In the event of heating faults, check the supply voltage, current draw and resistance against the manufacturer's specifications. For coolant-based heating, also check flow through the heating element and inspect it for leaks.

Allow the system's after-run cycle to finish before disconnecting lines. Collect AdBlue separately and cap open connections immediately. Replace cracked tanks and damaged filler necks; do not use general-purpose sealants or unapproved plastic repairs. Fit the specified seals and tighten flange fasteners and retaining straps to the manufacturer's specified values to prevent deformation.

If the wrong fluid has been added, a new cap alone is not enough: clean or replace the affected components in accordance with the manufacturer's procedure. Fill with clean AdBlue, carry out a fill-level recognition relearn or system test if required, and check the connections again for leaks. Braem's technical support can help match the tank, cap and required mounting parts to the chassis number.