Adblue System Fault Repair SCR and DEF - Audi, VW, Seat and Skoda Specialists in Guildford and Surrey
Location: Open View Farm, Epsom Rd, West Horsley, Leatherhead KT24 6AP
Open times: Open Mon - Fri, 8am - 5:30pm
Call: 01483 285792

Adblue System Fault


An Adblue system fault can be some of the trickiest do diagnose first time for some. At CT Cars we have devised a robust test plan to produce reliable results each time.

About Adblue®

Adblue is actually a brand name, a worldwide trademark of VDA. This chemical needs to be 32.5% solution of urea in deionised water. Without this solution the correct operation for an advanced pollution control technology installed in the exhaust system simply wouldn’t work. This exhaust technology is Selective Catalytic Reduction ( SCR ).

Adblue is a clear liquid and handling it is safe. The Urea solution encapsulates the toxic ammonia (needed for the depollution technology to function). Adblue does not mix with Diesel and has a separate tank ( reservoir ) for refilling.

The SCR process converts harmful nitrogen oxides produced by the vehicles engine into nitrogen and water using Adblue.

The Repair

A vehicle presented itself to us with a maximum range of 500 miles.  In addition, there was also an Adblue system fault message on the instrument cluster. The first step in out test plan was to read out fault codes, this is what we found on this particular vehicle.

  • P202A Reductant Tank Heater Control Circuit/Open.

This particular fault code is nice, due to the fact, a heater consists of a wire element. This circuit can have only two electrical states, Open or Closed. The heater elements are revealed by splitting the reductant pump assembly from the tank.

Its important that the heaters work correctly, for the reason that the reducing agent has to be kept within a certain temperature range. In other words, the water inside would either freeze or start to condense on the inside of the tank. The result of that causes the concentration to vary.

With the pump assembly on the bench. Manufacture wiring diagrams helped to decipher which pins on the control unit powered the heaters. In conclusion there was an open circuit within the elements.

Replacing the heater elements fixed this scenario, however, clearing the fault codes isn’t an option, because the message on the display would still be there, for instance. When using the manufacture diagnosis machine, there is a calibration routine that needs to be carried out before the SCR system is serviceable again.

Want to learn more or have some questions answered click here theAA have some Q&A’s

Why not read another post of ours EGR Faults Click Here

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