OK, the while accelerating onto the highway, my R55 Clubman (N12) triggered the engine light. It also began running rough with reduced power.
It's throwing these codes.

OBD reader read these codes
P0304 Cylinder 4 Misfire Detected
P2195 Oxygen sensor 1, bank 1 - signal stuck lean

Menu 14.0 on the dash showed this error code.
ERR01 A3ACh

So I want to try to determine what the cause is.
Is the misfire causing the sensor code? Or is the o2 sensor failure causing the misfire?

It's still under warranty, so is it safe to drive 20 miles to the dealer? Or should I have them tow it at their expense?
Thanks!

 

Does the CEL flash at all? If not, you're ok to drive the vehicle to the dealer.

* MINI DTC P0304 (0x2779 or 0x277A or 0x277B) - Cylinder 4 Misfire Detected
* MINI DTC P2195 (0x2AC3 or 0x2D33) - O2 Sensor Signal Stuck Lean (Bank 1 - Sensor 1)
* MINI DTC P2195 (0x2D35) - Pre-catalyst Oxygen Sensor, Plausibilty: Mixture Behind Catalytic Convertor too Rich

Start with the obvious and check cylinder 4's spark plug and ignition coil.
Check the gap of the plug, and set or replace plug is electrode is worn out.
If plug is good, check for failing ignition coil; one easy way to test a failing coil is to swap with a known good cylinder.
If the misfire "moves" to the swapped cylinder, it's the coil - simply replace.

The fuel trim faults could be the result of the misfire; especially when the more specific MINI fault says the fuel trim is too rich.
When a misfire occurs, unburned fuel exits the combustion chamber and into the exhaust downpipe airstream and the O2 sensor picks up a rich fuel condition.

- Erik

 

Thanks for the quick reply. Yes, the CEL is on. It runs rough at idle, but not too bad above idle.
What's the worst case if I drive to dealer like this? Destroy the catalyst with too much unburned fuel?
The engine runs much smoother on cold startup (open loop) but starts to run rough after a minute (closed loop), which leads me to believe it's the o2 sensor. Is that a good assumption?
Or it could be that in closed loop, it detects the extra fuel and causes a rougher misfire?

I would be comfortable checking the spark plug and coils, but I'm concern that MINI would then see that I was "tampering" with it and deny warranty claims.

 

You'd have to be seriously misfiring to cause any damage to the catalyst.
And a light misfire, without the CEL flashing, won't cause that... you're fine to drive.

Definitely possible...

You are you under warranty period?
If so, let the dealer fuss with it.
No reason for you to get dirty yet when you have proper coverage for such.

- Erik

 

Thanks Erik, but to clarify, the CEL is on. I believe it was showing yellow and red.

 

Just have them tow it, its all free! Why risk your car/ your safety/ your money when a simple phone call = 100% reduced risk!

 

Yes, I know that the CEL is on.
When the CEL flashes, that's when the ECU detects a serious misfire, which can cause damage to the catalyst over longer drive times.

- Erik

 

OK, I wasn't sure.
I did go out and start it up. The yellow CEL light was solid but it did flash for a few seconds every minute.
Is that the serious misfire you're referring to?
thanks.

 

Correct-a-mondo!

Now, as SooperCuperErik suggested, and I'm agreeing with, have the dealer grab it on their flatbed to their location.

- Erik

 

Definitely will do. Thanks for your input.

 

Long overdue update. Dealer said it was just a fouled spark plug.
It may have been filthy due to carbon deposits, but carbon cleaners didn't help, so maybe the plug just failed.

I would have liked to have seen the plug, but we were returning it from the lease.