Mechanic Advice

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'99 Corolla engine code P0125 (midwest.social)

submitted 1 week ago by [email protected] to c/[email protected]

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I'm trying to diagnose a p0125 code on my 99 corolla. Toyota forums seem to say Toyota didn't follow standards on this code and it is likely also the O2 sensor, can anyone confirm if this is the case?

I'm getting no other codes, and it will run for about 30 minutes before triggering again. Last time it triggered I saw exhaust smoke on the way home, which went away as soon as I reset the code. after clearing the code the exhaust while clear does seem to be rich smelling. Engine seems to run fine, I'm not noticing any performance issues, not signs of dipping oil/coolant amounts. coolant gauge is operating and hitting the halfway point normally.

I can't think of anything else but the O2 sensor but I expected rougher performance and don't really want to spend $125 on a part if I don't have to.

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[–] [email protected] 2 points 1 week ago

Late to the party but if it is a vacuum leak you can use some kind of flammable aerosol to find it. Quick little spurts around the throttle body and vacuum lines with the motor running and you'll hear the idle increase if it gets sucked into the engine and you'll identify where the leak is.

It sounds like a sensor to me though. Don't know which, but if it runs okay without smoke for a while after clearing codes then starts smoking after a drive and throws the MIL it sounds like it's fine when the computer is in open loop using predefined fuel mixtures, but when it goes into closed loop it starts dumping more fuel into the engine than is needed. If that's the case and the computer is forcing a rich condition you'll wanna get it figured out before the catalytic converter plugs and needs to be replaced.

If your familiar with motorcycles are you familiar with reading spark plugs? Probably worth pulling a few to try and see if the engine is experiencing a rich or lean condition.