AdBlue Off — disabling the AdBlue (SCR) system

AdBlue Off disables the selective catalytic reduction (SCR) system in the ECU software. The file removes the no-start countdown, urea system faults and power limitation. For tuners: send us the original file and get a ready-to-flash file with corrected checksums, on average in 30–60 minutes.

How the AdBlue (SCR) system works

AdBlue is a 32.5% solution of urea in demineralised water, specified by ISO 22241. The fluid itself does not clean the exhaust. In the hot gas the urea breaks down into ammonia (NH₃), and the ammonia then converts nitrogen oxides (NOx) into nitrogen and water on the SCR catalyst. This is how diesels meet Euro 6: for passenger cars that means no more than 80 mg of NOx per kilometre.

System components:

• AdBlue tank with level, temperature and fluid quality sensors and a built-in heater: the fluid freezes at about −11 °C.
• Supply module: a pump with a filter pressurises the line, and the line is heated too.
• Dosing injector sprays the fluid into the exhaust upstream of the SCR catalyst.
• NOx sensors before and after the catalyst, plus temperature sensors. The control unit uses them to calculate the dose and to check how well the system cleans the exhaust.
• Control unit. On most passenger cars and LCVs the SCR logic lives in the engine ECU. On some cars and on trucks dosing is handled by a separate unit (DCU, ACM).

Why the system fails and what happens next

An SCR fault is rarely fixed by topping up the fluid. The most common causes:

• Urea crystallises in the injector and the line, especially with short trips and after the car stands for a while.
• The tank heater fails. On many cars the heater and sensors are built into the tank and are only replaced together with it.
• The pump or supply module cannot hold pressure (code P20E8).
• NOx sensors fail. They are expensive and a frequent cause of the P20EE efficiency fault.
• Poor or diluted fluid: the quality sensor detects it immediately (P207F).
• The SCR catalyst itself loses efficiency.

It does not stop at a warning light. Under Euro 6 rules a car with an empty or faulty SCR system eventually refuses to start, and the countdown to that point runs in kilometres:

Example stages from Renault and Dacia owner manuals. Thresholds and messages differ between manufacturers, and some cars also limit power or speed.

If the cause is a fault rather than an empty tank, topping up will not stop the countdown. The component has to be repaired, or the issue solved in software.

What AdBlue Off changes in the software

Clearing faults with a scan tool is not enough: the ECU finds the fault again on its next self-check. So the logic in the ECU file itself is changed, and the unit stops controlling and monitoring the SCR system.

The rest of the engine calibration is unchanged. Checksums are recalculated, so the file is ready to flash straight away. DPF Off, EGR Off and Stage 1 can be done in the same file and the same order.

Which fault codes go away

Typical SCR system codes per SAE J2012. Manufacturers also use their own codes for the same faults.

How to order the file

1. Read the original file via OBD or on the bench (bench, boot) with the tool you use. We need an unmodified stock file.
2. Upload it to the portal and select ADBLUE OFF. You can add DPF, EGR and Stage 1 at the same time.
3. Get the finished file with recalculated checksums, on average within 30–60 minutes.
4. Flash the file, clear faults in all modules and make sure the countdown is gone.

If the car has a separate SCR unit (DCU) or the countdown is also stored in the instrument cluster, mention it in the order and we will advise for that specific vehicle.

What to do with the hardware

Removing components is not required for the software solution: as a rule the file works both with the system installed and with it removed. We still recommend:

• Remove the AdBlue injector and blank off its port, otherwise leftover fluid crystallises and leaks.
• Drain the tank so the fluid does not freeze or leak.
• NOx sensors: on some ECUs they can be removed after the solution, on others the sensor stays because its signal is used in other calculations. We will advise for your ECU.

Disabling SCR increases NOx emissions and changes the vehicle's emissions class. In the EU, the UK, the US and a number of other countries this is prohibited on public roads and may cause an inspection failure. The service is intended for tuners and is used where the law allows it: motorsport, off-road, export, vehicles not used on public roads. Responsibility for using the file lies with the vehicle owner.