VCDS code P0402

[ront]

Had bizarre experience today. I run a A6 3.o tdi Allroad (2014). Yesterday the Engine management system light started flashing. Then the emission control system light came on. Loss of power etc. Taking it to the garage today the Central warning lamp came on and the Diesel particulate warning appeared. Spent the day in the garage trying to find fault and came up with ERG - excessive flow. answer - replace ERG. Before doing anything else I took car out and 'blasted' for 1/2 an hour on the dual carriageway. Warning signs disappeared and car drove like it was supposed to. What was going on? Hoping to change fuel and give it a good blast once a week.

[ukgroucho]

You don't say which engine - I'd be interested - or describe your typical driving pattern (short trips, motorway etc.). Also how many miles has the car done?

When you say "change fuel" ... were you using super cheap budget fuel? What do you think you need to change to?

[Scott K]

Could be you are having dpf issues due to the journey types or it could be the egr valve is causing issues with the dpf.

[ront]

Well, engine is the CLAA, 218ps, 150kw, Have had the car only 6 weeks and have only done just under 1k miles with it. Had full service done just 2 weeks ago and no fault codes. Mileage is now just over 41k. Journeys so far have been a mixture of long(ish) and short drives ( min. of 15 miles.) I think I have only had 2 or 3 tank fills with supermarket diesel but recon this may be part cause of problems. Will now use Shell or BP. Will call in past garage tomorrow to discuss.

[ront]

Garage thought EGR was causing problems with the DPF but was not sure. Quoting £600 plus to fix the problem but I think they were not too sure whether this was the solution to the problem. Garage had tried a forced regen. They were very helpful and did not charge for all the time spent on car today.

[KevTrem]

Stop using supermarket fuel, the money you save at fill up you will loose in MPG and that's before repair bills. Stick to Shell etc and all should be fine. I have the same engine as you and commute to work on motorway doing about 11miles each way. Stick to normal fuel and stretch its legs in the lower gears every now and then.

[grant19841]

Garage thought EGR was causing problems with the DPF but was not sure. Quoting £600 plus to fix the problem but I think they were not too sure whether this was the solution to the problem. Garage had tried a forced regen. They were very helpful and did not charge for all the time spent on car today.

Forced regen, the oil should be change then along with the filter[emoji848].

As a regen is active the injectors force more fuel out so it reaches the dpf to increase its heat burn of excess soot, but the excess fuel will pass the piston and end up into the sump diluting the oil making it unsuitable for the engine.

Also cheaper fuel will cause more soot.


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[ront]

Thanks for all replies. DPF sorted but now have fault code for MAF. Still trying to figure out if it is the MAF or EGR.

[JamesMo]

When was your car registered? You state it's a 2014 with 41k miles - therefore it must be only just out of Audi warranty (if at all)? Just thinking that if it's in or close to being in warranty, I'd let Audi deal with it.

The supermarket fuel argument is in my experience invalid - I have run various diesel cars for over 10 years and over 300k miles with no issue at all and pretty much exclusively on supermarket fuel. All diesel fuel has to meet a minimum EN standard (EN590), which controls the minimum standard, therefore unless you are going for the premium branded stuff all the time the benefit is likely zero (there are plenty of conflicting views on this online - my experience say supermarket fuel is perfectly fine and is unlikely to be the only cause of your issue).

[Scott K]

If you bought it from a garage they should fix it for free as you will have a warranty.