help with log o2sensor fuel trim

[talongod]

Ok so my car is running lean but the check engine light is off so i logged my o2 sensor and fuel trim ........ MY o2 sensor 1 read 0-.04 (but when cold reads like .5) and o2 sensor 2 read .84-.98 at idle
STFT1 read 17 and LTFT1 read 12 at idle but on a 2nd gear pull the STFT read 0 and LTFT read 1 and my o2sensor 1 read 0-.02 and o2sensor2 read .96-.98
I can tell my o2sensor is bad but why isnt the check engine light on and what about the fuel trim readings??
sorry im a noob any input please

 

[DSMPowerTSi]

Ok so my car is running lean but the check engine light is off so i logged my o2 sensor and fuel trim ........ MY o2 sensor 1 read 0-.04 (but when cold reads like .5) and o2 sensor 2 read .84-.98 at idle
STFT1 read 17 and LTFT1 read 12 at idle but on a 2nd gear pull the STFT read 0 and LTFT read 1 and my o2sensor 1 read 0-.02 and o2sensor2 read .96-.98
I can tell my o2sensor is bad but why isnt the check engine light on and what about the fuel trim readings??
sorry im a noob any input please

Your car is running 17% too lean at idle. The CEL might not be on unless it runs rough and the ecu sees that the o2 sensor is faulty. The ECU doesnt use fuel trims or o2 sensor readings at WOT, the fuel trim goes back to 0. Hope that helps.

 

[talongod]

so if i get a new o2sensor it should fix my problem and run OK

 

[Staytuned]

If you know that you need a new O2 go and get it first of all. Secondly to set your fuel trims reset your ECU and then start it up and let it idle for a little while. Now take it out for a little spin to bring it up to good operating temp. Now let it idle at 1000 rpms look at your STFT and adjust accordingly...same for 2000 rpm's and 3000 rpm's. Your LTFT are an estimate that your ECU comes up with based on your STFT ....so if you get your STFT right you long term will fall in place. Now your WOT tuning is a whole different story. You want it slightly richer through the midrange rpm's and lean it out around 4000 rpm and on, all the time watching things like timing advance curve. You want to see around 17 degrees at the top of a WOT run.