I'm on my second i40 tourer 1.7grdi.... the first was the pre-facelift euro 5 on a '13 plate, which was bought pre-registered with 8 miles on the clock.
I am an airport private hire driver, covering mainly the southcoast to heathrow/gatwick 2 or 3 times a day, and cover between 300 to 500 miles a day, 5 days a week.
My cars are maintained at the main dealer for the duration of the warranty, which at 100,000, is around 14 months for me.
Once out of warranty, I use a reliable independent garage, who services 8 of the 13 i40's on our firm, and has experience of these cars which is probably greater than the main dealer, as some of the cars have covered a quarter of a million miles...(I do 93,000 miles a year, based on my current '16 plate having 166,000 showing, all driven by me, over the last 22 months from new). I intend to keep this one for three years, then part-ex it for my third one.
The previous '14 plate was generally reliable, apart from a gearbox problem at 14,000 miles, which resulted in a new gearbox under warranty.
It then continued in daily use as a long distance taxi, until at 22 months old, with 133,000 miles, the oil level started to rise on the dipstick (I luckily check my oil daily).
After a bit of research online, I figured it was failed regeneration, resulting in unburnt excess diesel finding it's way into the sump.
There had been no dashboard warning lights, and no logical reason for the repeated excessive attempts by the car to initiate repeated active regenerations, as almost all of my driving is on motorway/dual carriageway at 70mph.
I always filled the tank at the end of the day, so as to start with a full tank each morning, and always used premium fuel, usually Shell V-Power.
The garage had the injectors out, and sent them to the diesel specialist, who bench tested them and gave them a clean bill of health.
The garage them referred my to the diesel specialist for further investigation.
The specialist suggested it could just be HP pump seals, which are approx £30 plus vat, but sadly, the hp (fuel) pump is chain driven, and the timing chain is internal.
This mean't them trying to borrow the removal tool from Hyundai, which they said they were unable to do (no surprise), so the specialist manufactured a tool to do the job.
Once the fuel pump was off the car and bench tested, they told me it appeared fine, so it was probably the seals.They also advised that even though the pump tested fine on the bench, it could still be the problem, as it operates under higher temperatures on the car. The upshot was, I took up their suggestion of just fitting a new pump, as at 133k miles, it might give up some time soon anyway, and I had totted up lots of labour charges already.
As it turned out, the problem continued, so I made the decision to get shot of the car at a huge loss, and get a new one. I had spent £1139 so far, and lost 7 days work, so I had to make a bold decision!
Disposed of it on wednesday, drove a new one out the showroom on thursday 16th june 2016.
The new one (facelifted 2016 model - euro 6) has not had a hiccup, not even a warning light, in 166,000 miles from new. It is serviced every 20,000 miles in accordance with Hyundai's schedule, and has interim oil and filter changes every 10,000 miles. and that's it..... just tyres and brake pads/discs occasionally.
Now, to the point: A friend of mine, who runs 4 of these as airport cars on the same firm as me, had the same problem a year later, on a '14 plate euro 5 model, identical to my first one,
and in the intervening year since my experience, a cure has been found.
It turns out to be an ecu problem, and our garage referred my friend to a garage in town who specialises in ecu re-maps, and general performance tuning.
All they do apparently, is dump the programme from the ecu, and re-programme it with the new, up to date software, all licenced and official. Normal price around £550, but my friend got it for £450.
So in many cases it is an ecu/electronic problem, rather than a failed sensor, or being told you are driving the car incorrectly!!!!
Last point, to do with general sump overfill by garages.... I had this problem from new with the main dealer, and apparently it is because the handbook, and the official service data, says the sump refill is 5.3 litres.
I know from experience, as I do the interim oil and filter changes, and have done 15 of them on my drive in the last 4 years, that with an empty sump, and a new oil filter fitted, it takes EXACTLY 5 litres to bring the dipstick up to the full mark. Any more will take it over the max, and the official 5.3 litres will take it about half a centimetre over the maximum mark.
It doesn't help that the official data gives a figure that will result in an overfill. Every time.
I hope this helps.
PS. despite problems with the first model, I really rate these cars as hard working, reliable (post facelift), and apart from official parts prices, generally good value.