CEL...please help...P0171
 

i have an 05 scion tc and recently put all my stock parts back on.
i had a injen cai and megan racing header w/ antifouler

the cel came on then went off for about a week and now its back for good. code is
P0171 - system too lean bank 1

does anyone know exactly what that means and what is the problem and how do i go about fixing it? is it something with the 02 sensor? if so which one? i went to the dealership and they charge $98 just to take a look. i need to fix it ASAP

i need to clear the cel so i can pass smog and register my car in CA
erasing the code with an OBDII scanner wont pass smog.
any help is greatly appreciated and thanks in advance everybody.

if you get that code it usually means you have a vacuum leak.... when you put your stock intake back on make sure you didn't leave any hoses unattached and make sure everything is on all the way....as far as the header if you didn't get another manifold gasket and reused the one that was on it, air could just be seeping in through the flange and fooling the O2 sensor

well i def would get it checked out but a quick pass for inspection you might be able to disconnect the batterey to reset the ecu but dont know how long that will hold off the CEL, dont hold me to this, but it might be a bad fuel pump and filter, also it could be something as simple as a dirty MAF sensor, or just some Fuel Injector cleaner added to the gas tank might due the trick, im no mechanic but i would start with the easy and cheap solutions first such as cleaning the MAF sensor and throw some Lucas Oil Fuel Injector Cleaner in the tank

it might be the intake i was also thinking that. but it could also be the gasket. i used the megan racing gasket with the header but reused the old stock gasket with the manifold. thanks for the quick replies...anyone else know what else i can do? thanks

does too lean mean that there is too much air and not enough fuel? if so could it be the manifold gasket letting air seep through throwing the a/f ratio out of whack? this is just a guess can anyone confirm or comment on this? thanks again

when your running lean there is not enough air to gas i believe, and when you run rich there is to much gas to air?


Im sorry if this is incorrect but im fairly sure thats how it works

^^^ however i think you would definitly hear a leak in your header it sounds like poop

if it went out for a week, and now its back on for good as you say, maybe you just have a bad/dirty sensor, but the only realistic way of going about fixing it would be to bite the bullet and get the code dealt with at the dealership.

but if you already know the code, then they could at least give you some information about whats causing it. Obviously, if its running lean, there is not enough fuel and too much air, probably a combo of both.

Have you had any power loss that is noticeable to you? Any weird smells that are there that you havent smelt before?

You can definately tell when your runnin really rich, because ur exhaust has a very very distinct gas smell to it, but with running lean, that obviously would be the case!

how do i know if its bad/dirty? can i clean it some how? i noticed it was all black and dusty but arent all exhaust parts like that? thanks again

no power loss really and no weird smells

How long have you had the header on? Did you look under the hood to see any black around the exhaust manifold or with the engine running do you hear a ticking noise? usually signs of an exhaust leak...

there is false leans and true leans...

False lean = something like an exhaust leak

True lean = vacuum leak, clogged fuel filter or injectors, weak fuel pump

that you would need to find out at a dealer, I can't diagnose that via internet lol...

well if you would like to try and isolate the leak if there is one...buy a can of brake cleaner....run the engine at idle and do some short moderate sprays around the engine bay.... if the rpm's pick up you're close to the leak.... ie. spray by the throttle body, if the revs increase that's the closest source to the leak.... also try and spray the areas you put back together... most likely if that CEL came on after the stock parts were put on, you just missed something in the process.

"Lean" means the air/fuel ratio is higher than the ECU programming can correct for. This is worse than running too rich because the car may be knocking (detonation) which is very damaging to your engine internals.

Since the CEL come on after you re-installed your stock parts I would first carefully recheck your work. Intake - hose clamps tight, MAF sensor screws tight, etc. Exhaust manifold - recheck torque on all bolts, including the O2 sensor. The spring bolts @ the s-pipe are 32 ft-lb, O2 sensor is same, manifold bolts are 27 ft-lb IIRC.

Check the thread here on SL listing all the torque specs ...

Then clear the CEL and see if it stays gone.

Correct. Lean is typically much more detrimental, although super rich can be very bad as well if it is severe enough. It will actually cause poor oiling of the cylinders and engine damage if it is bad enough. But that is more rare than damage due to running too lean.

As has been said, the first step is to double check all work. My first guess is a vacuum leak of some kind. If all of that is good, you can go the bad sensor route. If you find an area you think is a vacuum leak, you can spray a tad bit of carb cleaner near it. If the engine rpm makes any sudden changes, you have found your vac leak.

I had this code about 2-3 times in the last few weeks, my gas mileage was shot and I couldn't figure out why. Switched spark plugs, cleaned air intake, did everything I could....

I cracked the hood with the car on and heard a hissing sound, placed my fingers over the vacuum line coming from the throttle body and guess what?! little tiny hole. Cut the line and reattached it and my CEL is gone and my gas mileage is back!

Check the lines really well.