cliffcoggin

Mark. Whether it was you that had the car mapped or a previous owner is beside the point that it's been mapped. Nobody does that without using the extra power and thus causing extra wear. Be that as it may, it's good you have had some testing done which should eliminate compression and other mechanical faults at the top of the engine, so we can move on to other possibilities. What mileage has the car done? Is it losing coolant? Has the EGR valve been cleaned? Has the DPF been regenerated recently?

As an ex-chemist I do not not believe that anything that survives passage through the engine without destroying it will any effect on carbon in the DPF. The internet is full of such snake oil treatments. This site https://garagewire.co.uk/news/game-changing-dpf-cleaner-is-a-profitable-solution/ indeed suggests that the DPF should be immersed overnight in the cleaner, not poured into the intake.

It sounds as if you have clapped out the engine with your mapping tweaks and some hard driving. Unfortunately a short engine life is the price for high performance.

Marcus. I have not done the job, but given that some A3s had 17 inch wheels instead of the 18 inch that you have at the moment it should be possible to fit smaller wheels with higher profile tyres. You would need to fit tyres of a large enough profile to ensure the overall diameter is unchanged, otherwise it would affect steering/suspension/drive ratios/speedometer.

Rob. I agree with Steve that it is likely to be EGR and/or DPF. How to remove them I do not know as mine is a 2 litre. I believe Gareth has a 1.6 litre so let's hope he will chip in.

That's unfortunate, but the money was not wasted in view of the warnings the car gave you.

But of course, it's Audi we are talking about.

Failure of the stop/start system is another symptom of a faulty battery. Make sure the replacement is suited for stop/start, which requires a better duty cycle than standard batteries can supply.

Adam. A defective battery can indeed cause false warnings in the instrument panel as well as other odd behaviour. It's why I asked about other symptoms. If you have been getting battery warnings recently then I would put money on it, if I was a betting man, being the cause of the false warnings. Your only realistic option is to fit a new battery. Charging the existing battery will not solve the problem.

Adam. It is not unknown for the A3 instrument cluster to develop faults and need repair or replacement, but it's a bit of a coincidence it went wrong during the storm. Can you get the car under cover for a day or two with the fuse boards and any connectors open to allow any moisture to dry? Maybe use a hair dryer, not a paint stripping hot air gun, to warm them. If that fails you may well need to have the cluster repaired, though wait for other responses on the forum before taking it out. Are there any other seemingly unrelated electronic problems such as limp mode, loss of cruise control etc that began at the same time?

Garages usually issue detailed invoices when you pay the bills. What do those invoices tell you was done?

You still have not told us yet what keeps happening.

Why are you renewing the calipers so often? To put it another way, what was wrong with them? I have had my A3 for 6 years and never touched the calipers except once to renew the pads.

If it is dual mass flywheel that is the likely cuprit and will have to be renewed. The springs break or become weak.

Did the noise start when you fitted the new tyres? If so, it's the tyres making the noise and there is nothing you can do about it. The noise from tyres varies a lot from brand to brand, just as the wet grip, the endurance, and the price also vary.

Max. It is not unknown for the instrument panel to suffer from the gremlins but as you have had it renovated we can rule it out. The next primary culprit is the battery. You may well have charged it, you may even measure 14 volts at the terminals, but it can still be defective. The only ways to test it are to have it deep discharge tested which involves applying a heavy load during the test, or to renew it.

The level needs to be measured while the car is level for obvious reasons. Have you run the engine yet to fill the filter?

Jack. Having opened the cooling system for EGR removal and a new thermostat, there is a good chance the system is now air locked. It's a common problem. The reduced or even complete loss of flow caused by the air lock would explain the lack of cabin heating, and the level loss as the coolant occaisionally boils away. I had some web sites bookmarked with recommendations on how to deal with the problem, however I can no longer find them, but I daresay you can find suitable information if you ask Mr. Google nicely.

What is MMI? Did it ever work? Who said contact a main dealer? What have you tried to resolve the problem? More information would help us to help you.

Sorry, I can not.

Ian. Gareth is right. Forget about error codes and warning lights until you have had the battery tested. That means a professional deep discharge test, not a domestic multimeter test which does not put enough load on the battery to give meaningful results.

https://duckduckgo.com/?q=audi+a3+service+manual&ia=web

I don't know what a BCCC engine is so I can't help there. Heavy steering could be caused by low tyre pressures, wrong toe-in, non-standard wheels/suspension. Check those before trying to alter the power assistance. During acceleration the gear changes should very smooth, almost imperceptible, when changing up. When the car slows and the gearbox changes down it can cause a slight jolt at each change, particularly in the three lowest gears. That is something I have noticed with mine and which I believe is normal. DSG gearboxes were not as refined then as they are now. Don't neglect the gearbox oil changes. The oil is expensive but a lot cheaper than failure of the control unit (Mechatronic I believe it is called). Diesel engine oils become black very quickly. It took me a while to accept this as normal after years of petrol engines.

A fault on that sensor is consistent with the lack of prior symptoms, so let's hope that solves the problem. Do please let us know the outcome. Don't be be unduly concerned at the lack of computer diagnosis. Unfortunately code readers are not as reliable as many expect and hope.

Maxine. There are hundreds, possibly thousands, of faults that could prevent the engine from starting, so the chances of diagnosing the problem from the tiny amount of information you supplied the forum so far are negligible. I shall assume the RAC mechanic checked the obvious things like fuel level, fuel pump, relays, coils, EMC etc. Do you have a full service history for the car? What mileage has the car done? Has the car displayed any other unusual symptoms before it failed such as smoke, high oil consumption, low power, high fuel consumption, coolant loss? if you can answer those questions we might, and I stress might, be able to home in on the fault. For a quicker result I suggest you get it diagnosed at a specialist VAG garage or, failing that, an Audi dealer though I must admit I don't have a high opinion of them. Did the trader you bought it from guarantee it in any way? Was that trader commercial or private? Your legal rights depend very much on precisely what he guaranteed and for how long. Some guarantees only last three months and cover so little that they are not worth the paper they are printed on.