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So my earlier post, 3rd time at the drag strip, I purchased some E85 race fuel and mixed up what should have been closer to E25 ratio of fuel in my car.
I added just over 2 gallons to the estimated 7 gallons of gas in the tank (app % plus gage looked accurate). I had 1/2 tank after mixing. I burnt almost 1/4 tank driving there, but got a CEL on the way (I had previously had one from my exhaust valve sticking and figured it was the same. The car went into competition mode and I launched it 5x. I also topped up with 93 octane on the way home so that should have diluted the E85 low enough.
The next day I tried to read the code and the door chime would not turn off so I pulled the negative battery cable for 10 minutes. The CEL went away. Drove the car 20 miles or so and stayed out, but came on when I started the car in the garage. The Code says P015B O2 Sensor Delayed Response - Lean to Rich (Bank 1 Sensor 1). Any experience with this? Did I damage an O2 sensor? Did I damage my car? My mechanic is pretty good and knows the mods (GM borla, Mamo throttle body and haltech hornet) I have and says they don't penalize warranty coverage for what I have done. I was hoping the issue would just clear itself.
The only other note is that I switched to lithium amazon type 48 battery, and have seen that low battery can cause the same codes (it has not acted low) is there a way to monitor volts with the car when it is not charging off alternator (running?)
Yeah you got too high on the Short term fuel trims. Once they hit like 25/30 percent added fuel which too much e85 will do they will trip a code. Remember your 93 octane is already 10 percent ethanol when you do the math on how much to add. Put 93 back in it , clear the code and it will probably go away.
Last edited by superramvette2; May 29, 2026 at 08:00 PM.
I agree with the above members. I was using the 5 to 1 ratio......5 gallons 93 octane and 1 gallon E85 mixture or 1/4 tank of 93 octane and 1 gallon E85. It worked and it made gains at the dragstrip with my bolt-ons. Just maybe it was too much E85 to the gallons you were using.
E30 question - got a CEL and code P015B
