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P0133 Trouble Code on 2001 Toyota Corolla

Hey everyone,

I’ve been getting a P0133 trouble code on my 2001 Toyota Corolla and am stumped as to what is causing it. I’ve ruled out the obvious stuff: I replaced the upstream O2 sensor and can vouch for the lack of exhaust leaks, since I replaced the entire exhaust system myself a few months back and checked again for leaks after getting the code a few weeks back. I haven’t replaced the spark plugs yet (they’re definitely overdue) or cleaned the MAF sensor (I’ve heard that these could be the culprits) and will probably do both this weekend. Any other ideas?

Thanks for your time and attention.

I think you’re right to give the car the service maintenance stuff it needs if it is at the recommended intervals. Spark plugs, air filter, check the idle rpm and timing, etc.

If it isn’t one of the O2 sensors that have failed, it must have something to do with the incoming air/fuel mixture. The MAF, MAP, coolant temp sensors, fuel pressure at the rail, leaking injectors are all suspect.

Do you have any pending codes?

If you are talking about the ‘check engine’ light, I heard the Car Guys say once on a show that the 2001 Corolla will display that warning when all that is needed is a new gas cap. I have had the ‘check engine’ warning 3 times during my ownership of my Corolla, and each time a new gas cap fixed the problem.

Did you replace the upstream O2 with an OEM unit?