2010 Evo GSR. Custom tuned on Accessport Tuner Race program. For 7 or so months no issues, last few weeks P0140 comes on every day. When tuner checks the box to disable rear O2 so the code wont come on anymore my A/F ratio at idle/cruise is pegged at 10:1. Un check the box and reflash and idle/cruise goes back to 14.7:1 ish.

Why is disabling the rear O2 affecting idle/cruise A/F ratio?

What is the solution to get rid of this every day P0140 SES?

I wouldn't mind if it was even once a week SES, but every 15 or so miles it comes back on every time I clear the code.

 

Have you replaced the factory O2 sensor with an aftermarket wideband sensor?

Marshall@COBB

 

Nope. I just ordered a new rear O2 sensor. Hopefully it gets rid of my ses light. Still not sure why I can't turn off my rear sensor like everyone else.

 

The rear O2 sensor is still used for adjusting fuel trims on these cars. If you completely remove (or disable) the rear sensor you will be relying on the front narrow band sensor for all fuel trims. This can be done however adjustments will likely need to be made to your map.

Marshall@COBB

 

Good to know. Thank you very much for the info.

 

Did replacing the front sensor resolve your issue?

Marshall@COBB

 

Nope, replaced the rear O2 sensor with a new one and still getting P0140 every day. I am at a total loss on what to do now.

 

Why not leave the Rear 02 enabled but turn off the P0140 CEL? It's an item you can turn off in AccessTuner Race. If you don't have emissions testing in your state just turn that off. If you do have emissions testing you'll need to leave it on (if it's off you will fail in some states) and get a spacer to put between the sensor and the bung. Also, don't DISABLE the rear 02 unless you remove it from the exhaust stream permanently, it'll get damaged otherwise.

If your tuner can't figure out something as simple as this you might want to look for a new tuner that specializes in the Evo X. This is a common thing and there's tons of threads/info about this on the forum.

 

I already have a spacer for the sensor. Spacer did not change a thing. Next time I go to my tuner I will have him try just turning off the P0140 and see what happens. I will have to do emissions some day, but for now I just want no SES light.