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audi a3 dpf

Audi A3 Diesel Particulate Filter (DPF)

Unless you are a mechanic or engineer, it can be difficult to fully appreciate how every little aspect of your Audi has its own function and responsibility. That is when everything is working correctly, of course.

But let’s be completely honest, when most people buy an Audi A3, it is because of performance and kerb appeal. But the intricate parts of the engine can ruin both of these instantly, and without them all working correctly, the car doesn’t run as it should.

We are aware that many people are not interested in how the engine works or how many nuts and bolts there are. Most Audi drivers just expect to have a perfectly working car – after all isn’t that what Audi have told us? Vorsprung Durch Technik, and all that!

Everything is rosy until that day when you start up your Audi A3 and are met with error codes, warning lights, Audi EMS, and DPF; what should you do?

This happened to a client of ours. The client had brought their Audi A3 (2016) to us after the vehicle warning lights appeared on the dashboard. A quick investigation showed that the Audi had the error code P2458 – Diesel Particulate Filter – Regeneration Duration.

The DPF is a filter that traps particulate matter such as soot and ash from the exhaust, which, if not maintained/replaced regularly, can cause expensive problems within your engine. The filter has been standard since 2009, and luckily we work with these every day at Fergies.

So, with warning lights, error codes, and (to put it bluntly!) the performance of the car being pretty darn terrible (certainly not Vorsprung Durch Technik) the client decided that this A3 needed a little attention from Fergies Audi experts. 

audi a3 diesel particulate filter


The testing confirmed the DPF error code and the data feedback confirmed the Audi A3 diagnosis of DPF regeneration. All filters have a process of self-cleaning and emptying, this being called regeneration on a diesel engine.

We knew now that we had to check the DPF and its levels. Our goal now was to find where exactly the problem was.

The DPF has passive and active regeneration. Passive being when the Audi A3 is driven at high speed, the exhaust temperature burns off the soot particles built up in the filter. But this relies on the car being driven at higher speeds for extended periods. But for most people, driving a car at high speed for a long time will probably only account for 5% of your driving experience.

So, active regeneration is built into the Audi system and means that when soot builds up in the filter to around 45%, this will cause the exhaust to heat up to burn those particles, and it will then clear the filter.

This process relies on the information being correctly recorded at the various sensors, from the engine to the exhaust.


At Fergies we use our 15-step diagnostic process to get to the root cause of all issues. We don’t guess. We don’t swap out parts. We do test rigorously and we do follow manufacturer guidelines. 

The first thing was to check the Audi Service & Repair history, and everything was checked and double-checked. With nothing too obvious noted, we went to the dealer diagnostic tool ODIS to look at the live data on the car.

Next, we checked the soot levels, where we noticed they were not above the DPF threshold, and the filter was not blocked. We then checked all the car filters and realised that the oil level was too high and diluted. Once we had drained the excess oil, our next move was to attempt the regeneration process again with ODIS.

The heat-up process was unsuccessful, and that was the problem. When we tested the exhaust temperature sensor, it showed that it was not working in the turbo phase. Our next move was to test all the sensors on the Audi A3 that run from the exhaust to the engine.

We also tested all the wiring to establish which one part wasn’t working and why.

Using our expertise of Audi cars and with DPF error codes, we located the problem quickly and discovered that the Exhaust Temperature wasn’t working, which was stopping the regen process. This was the problem with the Audi A3.


Now that we knew the problem, we replaced the temperature sensor and performed an oil and filter change. This allowed us to re-run the regeneration process of the DPF.

We didn’t waste any time on this job! The car was diagnosed, fixed and handed back to the client within a day. There is no better feeling for us than when we hand back a full functioning road safe car to another happy client.


Got a problem with your Audi? Contact our expert Audi technicians on 01635 778002 now! We would be happy to offer advice or book you in for a vehicle assessment.

Our assessments are designed to identify and diagnose the problem quickly and efficiently. We will have you back on the road in no time while saving your time and money.

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