I changed the oil an filter in my 308 1.6 hdi the oil is on the dash and engine is niosy

wow you even answered your own question
mechanic did not test the sensors
wow.

It appears to be a BIG problem and yet another reason not to buy Peugeot! Lots of info in the link;

https://www.google.com/search?q=2017+Peugeot+308+HDi%2C+urea+emissions+problem

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FREYA DYER IS A SPAMMER AND NEEDS BANNED FROM FIXYA

First make sure that the crankcase is filled with oil to specs. If so then the hassle has to be with either the oil pressure sender, the indicator, or the oil pump not doings it job.

Some are on the firewall engine side.

Low oil pressure starts from oil pump sounds like its blocked either in the pump filter or galleries in the enging. I would first call the dealer and check what filter system is on the pump which may require removal of the sump to replace or clean.

I would certainly not use a car with this problem as it could well cause engine failure. Try a good quality flush first and run the car for 20 minutes minimum on tick over. Remove and put a good quality oil in and do another oil change again if required a month later with a flush to make sure the gunge is out.

If this does not help do an oil pressure test and see what it comes out at checking the manufacturers recommended pressures. If you have changed the oil, pump filters and done a second oil change and still get low pressure then you may well have a faulty pump.

I would also check the oil pressure switch to make sure it s not giving a false reading. The loss of power sounds like Turbo failure and again dirty oil to the Turbo oil feed pipes could be restricitng flow, hence why regular flushing oil and filter change is important.

I would get the Turbo checked out same time as on this model it could well be a Turbo and engine change if its gone that far due to the metal particles contaminating the engine.

308 1.6 hdi 110bhp cam syncro voltage low any ideas?

The electrovalve that controls the turbo waste gate needs to be changed it costs around £40. It is located on the front lower part of the engine block. I have done lots of them they are a common fault after about 50000 miles.

yes these suffer bad on faulty turbos, i think yours is dead, let me know how u get on.
i know they carbon up inside which stops the oil getting in, really u need another oil change between servicing.

ı have a peugeot307 in 80300km I DON'T KNOW exactly when take it to care ,brake.steering wheel,gearshift hydraulic,trigger set etc when will they change in what kilometers Can you help me? Thank you already