I have a 2008 Cooper S with 32,000 miles on it. Stock with the exception of an Alta Cold-Air Intake (more on that in a moment). I bought it used in early December with intake already on it. It ran flawlessly for a month, but I've been getting yellow check-engine lights for the last several weeks. On two occasions I've gotten the solid yellow engine symbol, which stays on until reset, and a few times I've gotten the yellow "half-engine," reduced power symbol, which goes off after a short period. On a couple of instances when I got the half-engine light, the car ran rough at idle but was fine after I got it up to cruising speed. Otherwise, no detectable change in performance. The warning lights do not correspond to cold temps. If anything, they've happened on humid days, both warm and cool.

It has been into the dealership, and the code tells them the problem is with the "O2 Sensor before CAT" (sorry, I don't know the P code). They changed the O2 sensor but that didn't fix the problem, and they told me the fault was stemming from the Alta CAI providing too much air to the system. They suggested I return it back to the stock airbox, but at a cost of $372 for a replacement I didn't want to go that route. Then, after tinkering with the car it some more, they "reset the adaptations" and got the light to stay off. They thought that took care of the issue, but it didn't. Got the half-power light shortly after getting home and the solid light a week or so later (still on now). I have another appt. to bring it in.

Any thoughts on what the issue might be? CELs with the CAI system alone seem pretty rare. As far as I can tell, there is no aftermarket downpipe or exhaust on the car. Any help is appreciated.

 

MAF sensor?. Take it off and hit it w MAF cleaner. Oil from oiled filters can throw it.

 

Find out the code if you can. Its interesting that they got an abnormal 02 sensor code...and after fixing that and not solving the problem, to blame the aftermarket intake.

 

A follow-up on my issue: The dealer took another whack at the problem. They found that the O2 sensor had shorted out and that same sensor had been replaced last time I was in. So they looked some more and found corrosion on some of the connectors in the DME control unit. They got the okay from Mini to replace the DME unit and also replaced the engine section of the wiring harness. Had it back for 2 weeks now and no warning lights so far. Hopefully it's fixed. I'll post again if it isn't. By the way, the error code it was giving, at least on this most recent visit, was P0030.