Pat fluid or adblue is injected into the exhaust system . Some cars increase the diesel fuel supply into the engine to increase temperature to aid dpf regeneration. These are the ones that can dilute the oil and cause engine issues.

I'm going to have to disagree. There is a valve on top of the fuel tank that injects the Eolys into the fuel. It's connected to the fuel guage so puts in the right dose every time you fill up. The Eolys doesn't burn up in combustion and makes its way to the DPF.

Yes it can dose the fuel system as well as the dpf . Adblue is part of the scr system and is not in the fuel system. Some later Peugeot/ Citroen models have both a def tank and an adblue tank . Double trouble .,

Adblue and DEF are the same thing - Adblue is a German specification but widely used in Europe and Australia while Diesel Exhaust Fluid (DEF) is the name used in North America.

The DV6 is a PSA unit which, of course, is also used in Peugeot, Citroen etc models including our Berlingo.

AIUI the EOLYS fluid is held in a container at the rear of the vehicle with a tiny quantity being injected into the fuel tank when the car is refuelled. Its purpose is to allow the DPF to keep form becoming blocked with soot which is, instead, burned off.

The initial factory fill last around 95-100k miles. When the container needs to be refilled a message is displayed on the centre console to tell the owner. Ours did that exactly by the book.

A little later, just after a refuel, one of the engine warning lights came on and the car went into limp mode. Turned out the pump in the EOLYS tank had failed. Sorted but local specialist albeit at some cost.

As the OP's vehicle is 09 I'd expect it to have a PDF - if it's there you cannot miss it - but too early a model for Adblue to be in the mix.

Replacing the EOLYS tank including a dose of known good fluid would seem to be a good starting point. Whether, that done, other stuff needs recalibrating is outwith my experience.

Edited by Bromptonaut on 10/04/2023 at 10:20