Are you tuned? Maybe the tuner forgot to disable that code? I think it has to do with the catalytic converter. If you are just running the Cobb map, maybe the 02 sensor isn't plugged in all the way.

 

Just stage 2 cobb tuned. I check the harness connection all tight including exhaust and O2 sensor all good i cleared the code . So far no engine light. No rotten egg smell and cat rattle. So what could cause the P0420 code?

 

Probably too much vaping in your car.

 

Notes+for+2015-2017+STI+North+American+and+ADM+Spec]Confluence[/url]

 

?? What notes??

 

P0420 is generally a universal code for Catalytic Converter limit below threshold or something along those lines. P0420 indicates a failing catalytic converter. Correct me if im wrong but all Cobb downpipes are catted and have that high flow cat in them. Sounds like you may need a new down pipe soon. You can either replace the downpipe with another one or go for a catless down pipe.

 

So my buddy shop said its bad 02 that pulling the code. Replace the 02 now all good. Cat is reading correct

 

Hi, Newbie here, I change my Downpipe and Exhaust 2months ago, and then the check engine and cruise control light up yesterday, and i cant change the mode system in my 2018 wrx sti,
My down pipe is Invidia Downpipe-Catless Divorced Wastegate and my Exhaust is Tomei Extreme TI Titanium Catback Exhaust.

 

when the CEL pops & Cruise pops on, the car automatically puts you into a "limp" mode so you can't further damage the car. Since you're replying in an old thread, are you also getting a P0420 code? are you using a Cobb accessport? did you try what the original poster tried? (replace the 02 sensor).

 

I'm in the bay area. You may be limited to two tuners: GST and EQ Tuning in fairfield. GST (mike) is in... fremont? san jose? unsure.

You can call either of those two up and they will recommend you what to do next. Me personally, i would uninstall the downpipe and go back to stock. then unplug the battery to reset the ECU.

Drive it around for a bit and make sure the CEL doesnt pop on. After that, then decide on getting protuned or e-tuned. there's a lotta ways to go (i personally would buy a cobb accessport and take my parts to either GST or EQ and have them tune my stuff)

 

Thank you sir, for giving me a piece of advise. and is it okay to ask you something since you live here and bay area, do you know someone who can fix curb scratch in a wheel?.
Thank you very Much