CEL - P0133 - 2 months after changing 02 Sensor???

[elvislisa]

2004 Corolla - Changed my 02 Sensor two months ago due to a P0133 code that kept coming up. I replaced the sensor and the light went off. Now...two months later the code came up again!

I've read about the Manifold Gasket problem, but I had my mechanic check for that last time I was in before I changed the sensor. He said there wasn't a leak. I haven't noticed anything out of the normal - idling or loss of mpg. Another weird coincidence is that the code seems to only come on the day after I get gas (???).

So...now I'm a little dumbfounded and trying to decide if it's one of 4 things:
1.) I have a bad O2 Sensor (Denso 234-4800) which is unlikely
2.) I now have a leaking Manifold Gasket (going to try the spray test tonight)
3.) I need to get the ECU recalibrated (per TCB EG017-07) - Anyone done this? I never really heard of this before today
4.) Gas Cap problem - is there a specific code for this?

Anyway...I know some people were getting other codes along with the P0133 code like a P0171...but I'm only getting the one code. Any advice? I have a good mechanic, but I hate to keep throwing darts at this thing. You think it's one thing...get it fixed...it goes away...then it comes back! I know he can't recalibrate the ECU (dealer only) either and I hate to pay money for this as well if I don't have to. Why do these CEL codes have to be so specific - but yet so broad at the same time?!?

Thanks for any replies!!!

[ShawnM]

Has your mechanic tried to diagnose the cause of the problem or did he just check the manifold for leaks at your request? He should be able to easily test the response rate of the sensor to determine if you got a faulty one. As far as ECM updating, any reputable shop should have the equipment to do that these days through a j2534 passthrough device. It basically takes the updated info from the dealer database and flashes it to your ECU. As far as the possibility of a manifod gasket leak, you might want to check it when the engine is cold. If the leak is very minor then it may actually go away as the engine warms up and the rubber seal expands.

[elvislisa]

I believe he simply checked to see if there was any leaks. I'm not exactly sure how he did this to be honest. My mechanic (who owns his own shop) isn't totally up to date on everything so I'm not sure if he a j2534 passthrough device. He's not affiliated with any major/minor chain or anything or specific make of cars. He's one of those guys who will check out your car for you for free...and let you know what's wrong with it (my kind of guy). He charges what he thinks is fair...not based on some amount corporate put into his system. I've been going to him for years!

I know what you're saying about it being cold. It seems like the only times it (CEL) came on last year and this year was after a freeze. Then last night it got cool (about 50), but nowhere close to freezing (live in Florida).

I have to say that the whole calibrating the EUC seems odd to me...and I thought it would do it on it's own over time. Can I simply unplug the battery for 30 min to reset or is resetting not going to help?

I hate taking it back to him, but he's the only thing I can afford and I trust him to do a good job....just don't know if he has the equipment. I HATE taking my cars to the dealer for anything as you pay twice as much for everything - kinda like staying in a hospital!

That's why I was going to try to check and see if could find a leak on the manifold myself. If I can't...and it comes back on then I'm going to take it to him...just like to have a little information to help guide him in a specific direction sometimes because he doesn't specialize in Toyota or anything.

Thanks!!