[mrpete!]

Hi everyone,

This is my first post on Bimmerpost!

I have recently purchased my first BMW, a 2011 320i e90 LCI and I absolutely love it (except for the price of genuine parts).

I'm making this post as I'd love everyone's perspective and opinion on what to do in this situation. I'm mechanically minded enough to change my drive belt and replace parts, but not confident enough to change a rocker cover gasket yet.

Long story short, while driving late at night I had a check engine light come up, upon checking the codes they were P2189 and P2187 (System too lean at idle Bank 1 and 2).

I’ve done some diagnostics and was able to see from the data stream on my OBD2 device SHRTFT3 and SHRTFT4 are reading at 32.8 consistently, irrespective of driving condition. SHRTFTB1S2 reads at 99.2 and SHRTFTB3S2 read at 18.7 with fluctuations.

From my research, I understand this to mean the engine is running too lean (too much air in the fuel mixture).

I’ve tried cleaning my Mass Air Sensor and the issue persists. Further diagnostics revealed that O2S11 and O2S31 are both reading at -127.00 mA consistently, irrespective of if the car is in park or driving. Initially, I thought I may have had a vacuum leak somewhere in the system but would I be correct in thinking if this O2 sensor is outputting the same mA irrespective of what the car is doing then it’s likely faulty?

I’m thinking about replacing it, but I have no clue which sensor to order from a dealership.

I’ve been browsing RealOEM for the replacement part’s sensor but I’m confused on which sensor to order (https://www.realoem.com/bmw/enUS/sho...diagId=18_0744)

ChatGPT has helped me with this and suggested it’s the upstream oxygen sensor. Would anyone be able to offer some guidance on which part to order to fix this?

I’ve cleared the check engine light and it hasn’t come back after a day of driving, but the OBD data stream still shows these values, hence I think the light will just come back after a while.

Any guidance you can provide is greatly appreciated!

Sorry if this is a mess, I’m a armature mechanic who has learnt how to repair car’s by watching YouTube and asking ChatGPT.

[StradaRedlands]

mrpete! Welcome to the club! I can't speak to the CEL and why your're running lean, but I'll generically recommend investing in Protools or BimmerLink/Code or similar that will give you better intel over generic P codes. I've never been able to get ISTA up and running but that's even better!