Hi!

Octavia vRS TDI 2015 - For a while I've been experiencing constant DPF regens - the idle tick over constantly sits at 1K with the radiator fans running for a while after the ignition is turned off.

I drive motorway miles daily so it's not a symptom of short trips although on longer 2 trip ~2hrs the Particle Filter warning will appear but clears after ignition reset. I've noticed the regens are having a massive impact on fuel economy (only managing ~350 miles on a full tank when previously I could get around 400-420) as well as oil consumption.

I've had a local garage take a look and apparently found no fault and added a DPF additive to the fuel and told me to blast the car down the motorway - I interpret that as they couldn't be arsed to investigate it as they didn't even charge me...

Has anyone experienced a similar issue? I feel I'll need to point the garage at the potential causes as they're not going to find it on their own it seems...

Thanks!

Rather relevant is how many miles on the car. Have you not had a reading of the ash / oil ash content?

52 minutes ago, Evolution13 said:

Rather relevant is how many miles on the car. Have you not had a reading of the ash / oil ash content?

Mileage is ~132k and the garage reported the ash level to be around 60%.

My 2014 1.6 diesel doing similar and noticed a higher fuel consumption so wondering if i have an issue with the dpf however no warning light and my car is at 194k.

My mechanic was like yours when questioned him about the higer fuel consumption. Kinda out it down to age of car depsite me getting good mpg prior to service.

Fan didn't come on today despite doing small journeys but mpg was only 33 where other times mpg has been 50or so

Edited 20 June20 Jun by chrisski

vRS has the 184hp CUNA engine, right?

If so, how's your oil consumption? These engines LOVE to drink and burn oil. This can result in the DPF clogging prematurely. If you have excessive oil consumption (more than 1L per 1000km), then it could be your turbo as well.

However, if its the 184hp engine and you do have notable oil consumption, I suspect your DPF is just full and needs physical cleaning or even replacing.

On 20/06/2026 at 18:32, viper42 said:

vRS has the 184hp CUNA engine, right?

If so, how's your oil consumption? These engines LOVE to drink and burn oil. This can result in the DPF clogging prematurely. If you have excessive oil consumption (more than 1L per 1000km), then it could be your turbo as well.

However, if its the 184hp engine and you do have notable oil consumption, I suspect your DPF is just full and needs physical cleaning or even replacing.

Yes, it's the CUNA 184. It's currently in the garage and the mechanic is struggling to find any issues!

Constant regens, reduced range, 1l of oil per 600 miles and can't find a problem smh

Usual suspects on the CUNA are the piston rings, specifically the oil rings that like to clog form long-life oil services. They coke up with oil coal and get clogged. That way the oil that would otherwise just be "wiped" away now gets burnt. Most of the time you can't chemically clean them anymore, so you actually need to pull the pistons and replace the rings. Then hope that the cylinder walls still look alright.

The other mentioned suspect would be the turbo, depending on the mileage and how its been driven. However the piston rings are a common thing on the CUNA.

The CUNA specifically really is a horribly designed engine when it comes to that. Poor thermals and pistons oil rings that have holes that are too small and like to clog easily. Mix that with the poor thermals and long-life services and you get this as a result. Its basically the entire 1st gen EA888 1.8 TFSI story all over again.

So that would explain the high oil consumption. Do you think the DPF regen issue is totally unrelated?

It could very well be a mix of things. I'm not sure if you have logged your DPF activity, but this could be very telling about the issue.

A DPF regen on a healthy engine with no oil consumption will look something like this: You have a measured soot value and a calculated soot value. The regen of the DPF starts somewhere around 25g measured OR calculated. However, usually the calculated soot value raises faster and ultimately triggers the regen. This is dependant on the driving porfile, but you could say a normal regen interval is somewhere between 155 miles - 450 miles. Yes, the range is actually this wide. As an example, the measured value might still be at -0.3g (yes, actually in the minus. After a regen, this value often times is aroung -12g) while the calculated value is at 25g which triggers the regen.

I've experienced this myself on my Golf 7 GTD Variant with the same CUNA engine. Oil consumption is high, regen interval is around 30 miles and the measured value always shot up and triggered the regen. We ended up replacing the DPF as it was clogged prematurely from the oil consumption. After the replacement, the interval increased to normal levels and the calculated value triggered the regen again. But not for long, as the calculated value started to raise faster and faster, as the oil consumption got worse and worse. So the DPF got clogged quite fast again, even after the replacement. Ultimately this is to be expected. Also noteworthy, after replacing the DPF, the oil consumption worsened. This is likely hinting towards a broken turbo due to the change of exhaust backpressure after the DPF replacement.

Since my GTD had around 210k miles on it already and I've poured quite a lot of money into it already, I decided to sell it and not tackle the search for the oil consumption.

At this point it really depends on your budget, how much you love the car and if you're able to get it diagnosed and perhaps sorted for a good price. I really don't want to paint the devil to the wall, but out of all the common things wrong with the CUNA, you could be looking at needing to replace the piston rings, turbo, DPF and worst case, if the cylinder walls are damaged, even a replacement engine.

Other factors that would be cheaper to attempt and daignose first that could also lead to an increased oil consumption would be the valve cover, which houses the crankcase ventilation module. If the crankcase ventilation breaks, it can lead to increased oil consumption as well.