Originally Posted by elp_jc
Wishful thinking. If dealer suspects a mod caused the failure they simply deny coverage. Plus they 'flag' your car, so every dealership will be aware of it. So the burden of proof is on YOU, not to mention you'd need to hire a lawyer to bring a lawsuit. The more reasonable approach is arbitration, like it was mentioned above, but if you messed with the ECU (any tune, including disabling O2 sensors), you're probably going to lose either way. And in you deleted the cats (a federal offense), your odds are even more bleak.
I personally can't understand why people risk damaging their cars and/or losing their warranties with anything other than catbacks and/or wheels when car is covered, but to each his own. No smart person (juror or judge) is going to deny that tampering with the ECU could have changed something that fried the engine, so that M&M is not going to do crap for you since most owners reverse anything done anyway before a dealer's visit. All BMW has to do is provide evidence of tampering and you're toast. And yes, at least the factory can easily do that. Good luck man.
The dealer does not deny coverage or flag your car without going to BMW. The warranty is through BMW, not the dealer. The only role the dealer plays is to report the facts to BMW, who will ultimately make the decision on coverage. Most of the dealers don't care because they just want to get paid on whatever work they would need to do to get you back on the road. Furthermore, most dealers do not want to piss off their customers.
There is no risk of damage in replacing your exhaust with HFCs and a catback. We know this because many people have dynoed their cars, and measured AFR, with this setup. The stock programming is intelligent enough to keep everything safe.
Now if you remove the cats altogether, or buy a system which relocates them further downstream, there is a chance that you will run slightly lean in a very small area of the powerband. Will it cause damage over time significant enough to cause a failure? Who knows; I doubt it. My advice is to get a tune if you want to remove the cats.
I do agree that if you tamper with the ECU, then blow your engine, all bets are off - regardless of how solid the tune might be. Of course, there have been zero cases of engine problems related to ECU tunes reported here. You can bet the farm that if someone had a problem, they would be on this site bitching. The only programing related issues I've heard of are on supercharged cars, which obviously are no longer covered under warranty by BMW.