SES light :(

wstar

P0157 02 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
OBD-II Trouble Code: P0159 Oxygen Sensor Circuit Slow Response (Bank2, Sensor2)
If that's really the only thing you've ever done to the car (swap air filters for K&N): have you ever re-oiled them? Was it recent? If you over-oiled them, they can put a light coating of oil on the MAF sensors in your intake tubes.

That, or just dirty MAF sensors in general, can lead to P0159 pretty easily. P0157 is related but different, sounds more likely to be an actual O2 problem, but you never know with these things.

I'd run through all the common, easy stuff first that's remotely related:

(1) Clean your MAF sensors. They're easy to remove and replace, and you can buy MAF cleaner spray at the auto parts store. Be sure not to touch the sensors to anything, including your fingers. Just spray them down with the aerosol can from all angles once you remove them from the car.

(2) Check the whole intake tract for leaks on both sides of the engine. Look at the fittings between various intakes tubes, PCV tubes, throttle bodies, etc. Something may have come loose.

(3) Get under the car and check out the upper portion of the exhaust system, specifically around the catalytic converters. Check for loose bolts, blown gaskets, or leaks at any of the connections. Check the wiring harnesses for the 4x O2 sensors (one before and one after the catalyst on each side of the car) as well as the sensors themselves for damage (something you ran over could have hit them).

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