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.