Engine Code 1131 Need help
 

Well I been having nothing but problems with the F-150 I just bought. I recently been getting a check engine light so I finally went and bought a OBD2 Scanner. I pulled the codes and got the lower O2 sensor was bad and the 1131 code which is the H02 sensors is detecting that it's running lean. ANyways I went ahead and changed the lower O2 sensor and cleared the codes. Now I just took the truck for a ride and after about 5-10 minutes of driving the engine light went back on so I checked the codes again and it's a 1131. Can anyone help me out on why I keep pulling this lean code. Lean isn't something I want to have my motor running. Thanks for the help.
Erica

Could you maybe give some more info on your, mileage, year, etc...

-Kelly

Hey there.
First off I would highly recomend you get yourself a manual on CD. I got one at ebay and it is awsome for stuff like this. Go to ebay motors and do a search. I paid $14.

I took a look in my manual (it's a '98 manual but should be the same for most stuff) and this is some of what I came up with. It is real long so I only have some of it. If you need to check out more I can figure out how to copy it.

P1131 Bank 1 (cylinder 1) indicate the A/F ratio is correcting rich for an overly lean condition.

....Upstream HO2s not switching... fuel system not switching fuel trim...
Things to check:
excessive fuel pressure
leaking fuel injector(s)
low fuel pressure (running out of fuel)
contaminated fuel injector(s)
vapor recovery system
air leaks after MAF sensor
vaccum leaks
restricted air inlet
PCV system
improperly seated engine oil dipstick ....

I am no mechanic. I think tha example I am trying to show is that having the manual will give you a ton of information. It has been an invaluable tool for me.

Good luck!
Tom

We do need more info on your truck.
How is your o2 cross counts? Make sure you check them at idle as well as with RPM. This will help isolate your problem if that is the case. It should be running below 450 millivolts continuously if you are getting a lean code. If your cross counts are allright then you are probably dealing with a computer problem. I am assuming that your truck is a 96 up because obd2.
I would check fuel pressure next if you are in fact running lean. Also what is your injector pulse width? However I am curious about maybe someone doing some engine work and using the wrong type of sealant. If you don't use the type that says safe for o2 sensors then they are sure to be damaged. By the way how much was your scanner? Did you get a Rotunda or a generic? If it was a generic then that could come in really handy. Also where did you get it?

Hope I didn't go unnecessarily into detail here. Maybe it will help though.

Sorry was just pissed off over this and didn't think to say year etc.. Anyways it's a 97 F-150 4x4 I just changed the lower 02 sensor on it thinking it might help as I was getting that code too.
So now the 1131 says the upstream O2 sensor isn't switching? if so I guess I need to change it as well maybe? I am not really good with checking alot of things I do basic work on cars. I just got this truck and I know alot about Mopars which was the reason I didn't get a Dodge pickup cause the tranny issues with them are ridiculus. Anyways if anyone else has ideas I would appreciate it. I am leaving for FL in april with the truck to pickup my race car down there and I didn't want any problems towing it home back to Pittsburgh. Because I wouldn't be able to leave the trailor on the road if I broke down the truck would be left before I left the car. Well let me know if anyone else can help.
Erica

Be careful in what you start replacing the code is merely a clue as to what might be wrong with your truck. The route you chose to take could get expensive.
I know I also bought a code reader and thought I could solve my own problem.
Well, almost $380.00 dollars later in tools code reader parts etc.
In turned out to be some bad plugs wires in my case. Might be worth having a tech look at your truck its probably no big deal ...
;-)

I read your prevouis posts about the MIL so I'm familiar with the situation.

For some reason, the HO2 sensors seem to act up or fail after or during extended highway driving.

I too would recommend taking your truck to a mechanic before replacing anything else. An HO2 sensor not switching does not necessarily mean the HO2 sensor is bad.

Ford recommends following the procedure for P1130 if P1131 exists.

https://www.f150online.com/galleries...9-75-12404.gif

I'd think you should clean the MAF and see if that helps. A dirty MAF can cause a lean condition and the sensor is very sensitive to dirt and oil.

Just wanted to let everyone know the problem was fixed with the truck. It was the upper O2 sensor. My BF changed it out in 5 minutes and cleared the codes and it hasn't came back on since then. Thanks for the help.

Thanks for the update and the info on the fix. That could help someone out, someday!