Hooked up a cheap OBD2 scanner and found my 4Runner's been running rich for like 6 months without me noticing

I was just messing around with a $20 Bluetooth scanner from Amazon after my buddy said my exhaust smelled weird, and the fuel trim numbers were way off what they should be according to the Toyota forums, has anyone else had a sensor slowly go bad without throwing a check engine light?

2 comments

2 Comments

the_linda10d ago

Honestly, the "lazy O2 sensor" thing you mentioned is exactly what I'm scared of now. My numbers were sitting around plus 18 at idle and plus 14 on the highway, which is way too high but not enough to trip a code apparently. But here's the thing, did your Tacoma's trim stay consistently high, or did it bounce around depending on how long you drove? Because mine will drop down to like plus 8 after a good 20 minute drive, then creep back up when I'm stuck in traffic, which makes me think it's not just a simple leak, it's something that changes with heat. Did you check if your sensor was reading faster or slower after you cleaned the MAF, or did it just stay junk the whole time? I'm trying to figure out if I should throw a new upstream sensor at it or actually chase down a vacuum leak that only shows up when the engine is cold.

stellachen11d ago

So wait, you're telling me the long term fuel trim was sitting way out of range but the ECU never flagged it? That's the part that bugs me the most about these newer Toyotas, they'll happily adjust for a dying MAF or a cracked vacuum hose until the trim hits like plus 25 percent and then they just give up and throw a code. What were your actual numbers, were they like plus 15 or plus 20 at idle and cruise? Because I had a similar thing on my Tacoma where the upstream O2 sensor was getting lazy and reading slow, not dead, just slow, and the truck compensated for months before the cat finally started clogging up. Did you check the freeze frame data to see how long it's been adapting, or just the live numbers? That'll tell you if it's a sensor that's aging out versus an actual fuel or vacuum leak that the computer is trying to mask.