P204F96 Adblue error

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New Member
Aug 20, 2022
Sydney, Australia
W166 ML250
Hi, I have W166 ML250 with M251 engine, and recently had some AdBlue errors.
The Injector valve has gone open, replaced that one, the NOX sensor was giving odd errors, replaced that one.
Also replaced the Adblue pump, even though it probably did not need any replacement.
All errors have gone except for one,
P204F96 The AdBlue system (cylinder bank 1) has a malfunction. There is an internal component fault.
I have tested everything, except for the heated injection line (apparently this one is needed for very low temps, and here we never go below freezing.
The error persits.
Any ideas ?
The pump unit, and all tank components all tested OK.
The Nox sensor is new, a cheapie from Ebay, but produces no errors.
Xentry reset and re-learned all components, still no luck.
Can't find any explanation for that error anywhere.


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