2012 Corolla not completing all downstream O2 tests and catalyst

Ask our auto mechanics for help to all your Toyota questions.
Posts: 1
Joined: Wed Feb 09, 2022 9:14 pm

2012 Corolla not completing all downstream O2 tests and catalyst

Unread post by jmr1068204 » Wed Feb 09, 2022 10:46 pm

1.8L 4-cyclinder engine. Simply put the downstream O2 sensor is partially testing. It has a total of 5 tests and at varying times, it might show 2, 3 or even very rarely 4 of the 5 total tests completed. Then it goes back to an average of 2 or 3 tested again. The catalyst itself says it simply has not tested and the other tests that keep flipping back and forth also just say untested.

No codes in the system anywhere when I do an OBDII scan. I see live voltage on the downstream O2 when going down the road (up to 1V), the upper and lower O2 sensor are talking to one another, the fuel trims are being adjusted accordingly between the O2 sensors when accelerating/decelerating.

3 months ago, new iridium spark plugs and new air filter. Oil is clean and changed per mileage. We had this problem last year and somehow a Toyota tech got it to pass, but they're no longer there and didn't log what they did. The downstream O2 sensor was changed 3 times in the past 2 years because two different Toyota dealerships kept claiming it might be bad. New battery last year and the battery and alternator have recently tested good at two different places.

Car has 115K miles on it. It's 10 years old. Could it be the catalytic converter itself? It has never been changed. The other day, I put my hand down near the tail pipe at idle and it didn't feel like much air was coming out. I had someone take it to 2,000RPM while parked and I felt the tail pipe and it didn't seem like as much air as expected was coming out of it. I checked it again today and it felt fine at idle and was putting out plenty of air.

What am I missing? A repair shop that does catalytic converter installs wouldn't touch it. They swear it's a 'thermostat' issue even though the car isn't running hot. There is nothing different about the temp gauge. They claimed it could be 'stuck closed' and causing the O2 sensor to not fully test. I would expect that to make the car run hot or have temp issues.

Any suggestions?

User avatar
Posts: 2512
Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon


Unread post by carriedi » Thu Feb 10, 2022 4:06 am

are you talking about the readiness monitors are not completing? you say that you don't have any codes stored but what about pending codes?

what readiness monitors show up for your vehicle. Can you list them? Which ones say complete and what ones say not ready or not complete?

you should drive the vehicle while graphing the monitor fields while doing the drive cycle. My information shows 13 drive cycle graphs. Later drive cycles say to clear codes even if it shows no codes are present before performing the drive cycle.

here is cat drive cycle 1. Warn engine temp is 167F or higher
cat drive cycle.jpg

  • Similar Topics
    Last post