Hey guys i have recently installed my magnaflow catback and i ran that for about a week and a half... put about 400 miles on the car, Alta Intake was in before and still in.

randomly as im just going around a corner, at a normal speed not accelerating, i get the SES Light. Read the Code and it showed up P2270 which is lean condition.... strange i thought to myself, esspecially since i was normal driving at a leisurly pace. I did also run my MINI Hard a few days before this since i love the note of the exhaust and the response it gave me..... cleared it that day.... ran good for another 2 weeks. on Monday i popped the code sitting at a red light. Sunday i was in the mountains doing a road rally coarse very enthusiaticly. i feel like if the car was actually running lean i would have popped the code while in the mountains running hard

The car seems to run fine, idles fine, still has heaps of power.

i havent trying taking the O2 sensor out and cleaning it yet since i thought the first time was a fluke....

i also thought maybe i have a bad injector, but if i had a bad injector it wouldnt be able to run the duty cycle at high RPM?

any thoughts?

'05 JCW with alta intake and magnaflow exhaust, other than that it is stock

 

This "could" be your exhaust, one of the ways the ECU interprets lean/rich is by reading the variation between the O2 sensors, if it persists try the spark plug spacer or L shaped spacer in the rear O2 sensor bung, a cheap test.

 

Because the code P2270 decodes as O2 Sensor Signal stuck lean - bank 1 sensor 2. . I would look at the connections and maybe take it out and check out its condition.
I would also check the entire exhaust system for any leaks at any of the flanges.
I would also have the code cleared and see if it returns.
You can also try also resetting the ECU as seen here.
How to Reset the ECU:

1. With the key in the ignition, but in the off position, press and hold down the odometer reset button with one hand, while holding the button down, switch the key in the ignition to position 1 (first click) with the other hand. The screen will have a number and the word “tESt”. Scroll through the numbers by pressing the odometer rest button, through to 19 and wait a moment. (Note: the number order is: 1,2,10,19) The message will say 19 "L i-off", flash to "L i-on", and back to "L i-off" again. When "log i-off" appears, press the odometer rest button again. You are now in the system. Scroll through to 21. tESt and wait a moment. 21.0 rESEt will come up. Press the button once.
2. Your gauges will now make some sounds and movements.
3. Once the lights come back on start your car. You have now reset your ECU and your MINI is now ready to relearn the new mods and your driving style.

Here is a list of all the tests on your MINI:
1.0 Chassis number
1.1 Kilometer count
1.2 Parts number
1.3 Coding-, Diagnostic- and Bus-index
1.4 Production Date (Calendar week/year)
1.5 Hard- and Software status
1.6 Injector status, Cylinder count, Engine factor.
2.0 Comb system Test
3.0 Service interval counter
4.0 Actual fuel consumption in l/100km. eg.0154 = 15,4 liters/100kms.
4.1 Consumption in liters/100kms.
5.0 Distance consumption in l/100kms.
5.1 Actual rest distance with available fuel in Kms.
6.0 Actual amount of fuel in tank. eg. 123321 =12,3liters left 32,1 liters right
6.1 Total amount of fuel in tank.
6.2 Show value of Fuel gauge.
1= both senders OK, 2= sender failure, 3=ti signal implausible (no reading)
7.0 Actual coolant temp.
7.1 Actual outside temp.
7.2 Actual engine revs.
7.3 Actual speed
8.0 Hexadecimal readings of menu 7.0 to 7.3
9.0 Actual on board voltage (Battery)
10.0 Land codes
11.0 Unit codes
12.0 No function
13.0 Gong test
14.0 - 14.4 On board diagnostic codes. eg 000000 = no failures
15.0 - 18.0 No function
19.0 On/Off for Test menu.
20.0 Correction factor for Fuel consumption Formula for correction:
Shown consumption x 1000 / user defined consumption
Push the trip reset button to begin the correction. Numbers count up from 0-9, when correct number shows push trip reset button.
20.1 Sets 10ths. for consumption factor
20.2 Sets 100ths. and 1000ths. For consumption factor
20.3 saves the new consumption factor and shows new value
21.0 Software reset. (Same as disconnecting battery)

 

i just reset the ecu a few weeks back, ran fine, did MOT, a few other enthusiastic drives. short and long.

did the ecu reset basically 1 day after bram posted

drove to work today, 55 mph constant use of throttle, not in a hurry or anything, saying i was doing roughly 36 mpg at the time in the instantaneous.

then click, ses light came on.... i havent read the code yet but i can almost gaurentee that its this same code

 

I am relatively new to Mini's but been working on cars for a long time and never seen switching to a catback exhaust itself cause a lean condition. If you had a decent exhaust leak between the rear of the exhaust manifold and the catback exhaust, could cause the rear O2 sensor reading to be off...maybe...but I doudt that would cause a light.

However, I agree that I would start by checking for a leak in the exhaust manifold itself and the mounting point between exhaust manifold and catback. And, if that is not it, check the wiring and condition of the O2's.

 

yeah ill have to give everything a good look through, i know im not leaking, made sue of that when putting it in, and if it was before the cat, it would be very loud, which im not experiencing..... i need to check the o2 sensor