If you drive a modern European diesel—whether it's a VW TDI, a Mercedes Sprinter, or an imported Citroen/Peugeot—you know the panic of the "AdBlue Emission Fault." It usually starts with a warning light, then a countdown mileage, and finally, the car refuses to start.
Dealers often quote thousands to replace the entire tank and heater assembly. But in many cases, the fix is much simpler. In this guide, we’re breaking down how to diagnose, clean, and reset the Denox system using the iCarsoft CR Ultra P.
Guide Overview:
1. Identifying the Enemy: Common Fault Codes
When the "Engine Management Light" or "UREA" light pops up, you need to know exactly what you are dealing with. Using the iCarsoft CR Ultra P, we pulled the following confirmed codes from the vehicle in our test (a 2.0L Diesel):
• P20F6: Reductant Injection Valve Stuck Open
• P20A2: Reductant Purge Control Valve Performance
• P20E8: Reductant Pressure Too Low
• P20E9: Reductant Pressure Too High
2. Why is this happening?
It’s not always a broken part. The culprit is usually Crystallization.
AdBlue (Diesel Exhaust Fluid) is prone to crystallizing into a white, chalky substance when exposed to air or when the system isn't used frequently on long highway runs. These crystals clog the injector nozzle (located in the exhaust pipe) or the pressure sensor. When the computer can't dose the fluid, it throws a fit and eventually puts the car in "Limp Mode."
3. The 3-Step Fix
Before you spend money on new parts, try the "cleaning method."
On most Euro diesels, the AdBlue injector is located downstream on the exhaust. It’s often held in by a clamp. Remove the undertray engine cover if necessary to get access.
If the tip looks like a rock of white salt, that's your problem. Clean it thoroughly with warm water (AdBlue dissolves in water). If cleaning doesn't work, you may need to replace the sensor with an OEM unit.
Warning: Do not use cheap aftermarket sensors; they rarely communicate correctly with the ECU.
This is where most DIYers get stuck. Even if you clean or replace the part, the car remembers the fault. You cannot just clear the code with a $20 dongle; you must perform a system "Reinitialization."
4. How to Reset the Denox System
You need a bi-directional tool like the iCarsoft CR Ultra P to tell the ECU that the repair has been done. Here is the process we used:
- Step 1: Select your vehicle make/model on the CR Ultra P.
- Step 2: Navigate to Special Functions > Service Action > Emission.
- Step 3: Select "Reinitialization of the DENOX system" or "Reset UREA/AdBlue lock."
- Step 4: The tool will guide you to cycle the ignition (Turn Off, Wait, Turn On). This registers the new values.
- Step 5: Perform a final "Clear DTC" scan.
Once completed, take the car for a 15-minute drive. The lights should extinguish, and full power should be restored.
5. Frequently Asked Questions (FAQ)
A: While remapping to delete the AdBlue system is physically possible (and mentioned in the video), it is illegal for road use in the US and Europe due to emission regulations. We recommend fixing the sensor to keep the car legal and resaleable.
A: Sometimes. A long highway run can generate enough heat to burn off mild soot in the DPF, but it rarely clears a crystallized injector. Physical cleaning or replacement is usually required.
A: Emission-related faults are "sticky." The ECU needs a specific command to reset the AdBlue counter and learned values. Standard code readers cannot do this; you need a tool with "Adaptation" or "Special Function" capabilities like the CR Ultra P.
Don't let a clogged sensor leave you stranded. Get the professional tool that fixes it.
Shop iCarsoft CR Ultra P
Fast Shipping from US Warehouse
