Adblue failure, what next?

AdBlue Fault – What's Next? Error Codes, Causes, and Effective Diagnostics

Exhaust gas aftertreatment systems in modern diesel engines, such as AdBlue / SCR (Selective Catalytic Reduction) , are necessary to meet Euro 6 / Euro 7 standards. From the driver's point of view (especially Citroen, Peugeot, Audi, Volkswagen, Opel, Renault owners), however, they are:

• complicated,

• expensive to maintain,

• susceptible to faults.

Therefore, when receiving messages such as "AdBlue system fault" , " exhaust gas aftertreatment system failure " or counting down the kilometers to the start inhibit, it is crucial to understand the structure of the system, typical error codes and diagnostic methods .

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The most common AdBlue / SCR error codes – what do they mean?

The following groups of diagnostic trouble codes (DTCs) most commonly appear with AdBlue (SCR) systems. These are the codes that users most often enter into Google along with the phrase "AdBlue error what does it mean?"

1. Errors related to NOx sensors

• P2200–P2204 – NOx sensor circuit problems.

• P229F – NOx sensor fault.

• P2A00 – NOx sensor problem, signal out of range.

• P204F – Incorrect NOx reduction system performance.

2. AdBlue dosing system errors

• P20E8 – low pressure in the AdBlue system.

• P20E9 – pressure in the AdBlue system too high.

• P2047–P2049 – AdBlue injector circuit problem.

• P2033 – AdBlue injector overheating.

3. Errors related to the quality or presence of AdBlue

• P207F – AdBlue quality not meeting requirements.

• P20EE – incorrect SCR catalyst efficiency (often related to AdBlue quality).

• P203F – low AdBlue level in the tank.

4. Temperature and AdBlue level sensor errors

• P205B–P205D – AdBlue level sensor problems.

• P206A – incorrect signal from the AdBlue fluid quality sensor.

• P20BD–P20BF – AdBlue fluid temperature sensor fault.

5. Errors related to the AdBlue pump

• P20E0–P20E2 – problem with the operation of the AdBlue pump.

• P20C0 – AdBlue pump mechanical jam.

6. AdBlue / SCR system errors

• P16CF – communication problem in the AdBlue system.

• P2BA9 – NOx emission limit exceeded – problem with the SCR system.

7. Other errors related to AdBlue and DPF

• P2032–P2034 – exhaust gas temperature sensor before/after the SCR catalytic converter.

• P2002 – Incorrect efficiency of the diesel particulate filter (DPF – indirectly related to AdBlue).

• P249C – problems with the reductant injection system (e.g. AdBlue freezing).

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How does the AdBlue (SCR) system work?

AdBlue is the commercial name for a 32% solution of urea in water . Urea is a compound known from biology (it occurs in organisms), but in the automotive industry it is produced synthetically.

Purpose of action – what is AdBlue for?

The main purpose of the AdBlue system is to reduce nitrogen oxides (NOx) . Modern diesel engines operate on a very lean mixture:

• this ensures low fuel consumption and good dynamics,

• but it produces large amounts of nitrogen oxides (NOx), which are harmful to health and contribute to lung diseases.

AdBlue / SCR system operation stages

1. AdBlue injection
   Urea is injected via a precision AdBlue injector into the exhaust system upstream of the SCR catalytic converter.

2. Thermal decomposition of AdBlue
   For the system to function properly, the exhaust gases must reach a sufficiently high temperature.
   In the mixer (after the injector):

   • urea evaporates,

   • decomposes into ammonia, water and isocyanic acid,

   • Isocyanic acid combines with water to create additional ammonia and CO₂.

3. SCR reduction
   Ammonia (NH₃) reacts with nitrogen oxides (NOx) in the SCR (Selective Catalytic Reduction) catalyst.

4. The end product of the reaction
   Nitrogen oxides (NOx) are converted into:

   • harmless water vapor,

   • pure nitrogen (N₂).

An efficient SCR catalytic converter can reduce NOx by 70–90% .

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Key components of the AdBlue / SCR system

The AdBlue system is monitored by many sensors and actuators:

• AdBlue tank
  It contains the fluid and often also the AdBlue controller, pump and heaters .
  Heaters are necessary because AdBlue freezes at around -11°C .

• AdBlue pump
  Generates working pressure – in a properly functioning system, usually around 4–6 bar .

• Sensors
  Monitored by:

  • level,

  • pressure,

  • AdBlue fluid temperature.

• NOx probes
  They measure the content of nitrogen oxides in exhaust gases (often in ppm – parts per million).
  Typically, two NOx sensors are used – before and after the SCR catalytic converter.

• SCR catalytic converter
  Equipped with a special chemical coating that allows ammonia to react with NOx.

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What can a driver do in the event of an AdBlue fault?

The driver has an influence on both prevention and reaction in the event of an AdBlue system fault message.

1. Conscious use and prevention

• Fuel and AdBlue filling
  AdBlue consumption in passenger cars is usually 1–3 liters / 1000 km .
  It is worth refilling AdBlue before the reserve level comes on in order to:

  • do not overload the system,

  • avoid level errors.

• Use of fuel additives (DPF/SCR)
  To protect the DPF filter (closely linked to the SCR) and limit frequent regenerations that increase the amount of unburned oil in the oil:

  • fuel additives can be used, e.g. Liqui Moly 2650 ,

  • they reduce the soot burning temperature by approximately 100°C ,

  • support passive regeneration (during normal driving, without forced burnout).

• Taking care of the engine condition
  The proper operation of SCR/DPF systems is directly related to engine condition. It is recommended to:

  • more frequent oil changes ( 30,000 km intervals are too long ),

  • using engine flushes to reduce deposits,

  • replacing washers under injectors ,

  • regular cleaning of the intake system (in diesel engines, soot + oil mist accumulates).

2. Reaction to failure – messages and km counter to block

When the AdBlue system stops working properly:

• a message like "AdBlue system fault / exhaust gas aftertreatment system failure" appears on the dashboard,

• After a certain distance (e.g. 1000 km ), the controller may block the possibility of restarting the engine .

Because the AdBlue system works in tandem with the DPF:

• In case of problems with the DPF (e.g. frequent burning ), it is worth creating conditions for regeneration:

  • steady driving for 15–20 minutes ,

• If the DPF light comes on, the car cannot cope with regeneration and requires help (diagnosis).

Too frequent regeneration (e.g. every 200–300 km ) may:

• cause the oil level to rise (oil flows into the oil pan),

• lead to oil dilution and engine damage – the cause must be found and removed as soon as possible .

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Methods for diagnosing and repairing AdBlue faults

AdBlue system faults may include:

• electronics (modules, controllers, sensors),

• mechanical components (pump, injector, valves),

• installation (harnesses, connectors),

• as well as cooperating systems, such as DPF or injection system.

1. Computer diagnostics of the AdBlue system

Diagnosis should always start by connecting a diagnostic computer (e.g. VCDS, Thinkcar, Autoxscan ) and:

1. Reading error codes
   Errors often indicate:

   • damage to tank components (level, pressure, temperature sensor),

   • damage to the tank heater or cables.

2. Verification of AdBlue operating parameters

   • checking whether the system reaches the required pressure ( approx. 4–6 bar ),

   • urea temperature control.

3. NOx probe checks

   • comparison of NOx values ​​(ppm) before and after the SCR catalyst ,

   • An efficient system should significantly reduce NOx levels .

4. Execution tests

   • running the AdBlue injector test,

   • checking the spray pattern – the injector should spray (atomize) , not "pour" in a stream.

2. Physical diagnostics and fault location

Many AdBlue problems are mechanical or electrical in nature and can be detected by visual inspection:

• Leaking AdBlue injector

  • leads to urea dripping into the exhaust,

  • manifests itself as a white coating/stains inside the DPF or catalytic converter,

  • crystallizing urea can lead to physical clogging of the filter - the injector must be replaced.

• AdBlue control module failure

  • in some Audi models (A4, A5, Q7, A8) a common fault is damage to the electronics of the controller bolted to the tank,

  • the reason may be a faulty housing design (e.g. a vent hole through which moisture enters),

  • water causes corrosion (so-called "rotting" of the module) - this usually ends with replacing the controller .

• Damage to the electrical installation

  • you need to check the harness for breaks and short circuits,

  • Moisture can lead to crumbling insulation and broken wires.

• Checking DPF-related components

  • Since DPF and SCR work together , an AdBlue fault may affect the filter filling,

  • if the pressure difference across the DPF is too high (e.g. > 350–450 mbar at full load ),

    • you need to decide on: regeneration, professional cleaning or replacement of the DPF .

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Should I remove AdBlue? An important note at the end

Removing the AdBlue system (unprogramming it from the ECU):

• is often chosen by drivers due to high repair costs ,

• It usually does not require physical disassembly of components (many workshops leave the components in place).

However, please remember that:

• a properly functioning AdBlue / SCR system is designed to meet exhaust emission standards,

• its deactivation may be inconsistent with the regulations regarding the approval of the vehicle for use on public roads,

• It is recommended to repair the system so that it operates in accordance with the manufacturer's specifications, environmental standards and legal requirements.

Therefore, the best approach to the message "AdBlue system fault - what next?" is:

1. correct computer + physical diagnostics ,

2. determining the cause (sensor, pump, controller, injector, installation, DPF, engine),

3. removing the cause , not just deleting errors or bypassing the system in the software.