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Fault code

P20EE fault code.

This code comes up with one known fault.

Generic code

Code type

Engine and drivetrain

System

SCR catalyst efficiency is below the threshold

The SCR catalyst uses AdBlue to cut the nitrogen oxide content of the exhaust gas. The engine control unit measured a higher NOx value after the catalyst than allowed. The dosing, the catalyst or the NOx sensor can be the cause.

The code tells you what the control unit measured, not which part has failed. The same code has several possible causes.

Which known faults it comes up with

AdBlue / SCR: NOx sensor and crystallising dosing valve

expensive

On AdBlue (SCR) diesels the NOx sensor after the catalyst ages, and the tip of the dosing valve crystallises. An AdBlue warning appears on the dash, often with a countdown ("X km of starts remaining"), while the tank is full. Crystallisation typically forms with short trip, urban use, or from poor quality AdBlue; on a car standing below freezing the circuit can freeze up too.

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At the end of the countdown there is a start inhibit: the car can become undriveable until it is repaired. The fault is not always the SCR catalyst: the cause is the sensor or the dosing valve.

between 100,000 and 160,000 km

What to check

  • Check whether there is an AdBlue filler (next to the fuel cap or in the boot): if there is not, this car does not have the system
  • Read all the dash messages after switching the ignition on: there should be no AdBlue warning and no km countdown
  • Ask for a fault code read: the codes P20EE, P2202 and P229F belong here. A cleared code comes back after a few tens of kilometres
2 more steps in the write-up

Information, not an expert opinion

We write the descriptions, and we put the source next to them. A person reviews them before they go out. They are still information, not a technical expert opinion.

  • A fault on the list does not mean the car you are looking at has it.
  • A fault missing from the list does not mean the model is fault-free. Write-ups are made model by model. Not all of them are done.
  • You decide whether to buy. This is no substitute for an inspection. That needs a workshop and a history check.
Details in the terms