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Transmission drained and Double the oil during oil change

I was doing an oil change and I accidently drained the transmission fluid and added oil to the oil reservoir. I drove it (with little to no transmission fluid and way too much oil) about a half mile and it began smoking badly. I fixed the problem but now engine light is on and the code is reading that something is wrong with the Cat. Conv. I’m not sure if it actually is the Cat. or possibly the O2 Sensor or something else?

I’d first replace the O2 sensor…and see if that clears it up. But don’t discount a bad cat, since the burning oil can damage a convertor. Only saving grace is the fact you only drove it 1/2 mile…so it’s more and likely just an O2.

thanks. You think upstream or downstream first?

It would help if we had the exact code.

I’m always confused how this can happen. Didn’t you check the dipstick after filling the oil? Wasn’t it way over the maximum line?

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I just figured it was empty so I put in about 3 quarts knowing that it took 4 or 5, then I noticed. It sucks being a flawed human.

After reading that I need more coffee.

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the code is PO420 (01/02) and PO420 P (01/02)

First (and cheapest) thing I’d try is go on a highway and take a 50 mile or so high speed drive (obey speed limits) to try and burn off the deposits.

Already have. It’s been like this for a couple of years.

Hopefully, AFTER the OP has filled the transmission to the “full” mark with the correct spec trans fluid. Nowhere does the OP mention if he has actually refilled the transmission–which could already be “toast” as a result of driving it “dry”.

If I’m reading OP’s last post right, he did this 2 years ago, so if the transmission isn’t dead by now it’s probably OK.

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After that coffee I would appreciate any suggestions you might have. The code is PO420 (01/02) and PO420 P (01/02). Thanks

Catalytic efficiency below threshold.

This could mean both sensors (there’s one before, and one after the catalytic converter) are coated in oil and therefore unable to do their jobs, and therefore returning similar values which tricks the computer into thinking the cat isn’t doing its job.

It could also mean the catalytic converter is borked and actually isn’t doing its job.

As others have said my first step would be to replace the oxygen sensors, as that’s pretty cheap and easy. If that doesn’t make the code go away, it’s time to be looking at the cat itself, which will be more expensive.

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what kind of car are we talking about here?

after running with cat codes for 2ish years, you could very well have toasted the catalytic converter. This code may have nothing to do with your overfill faux pas of years gone by…

thanks, this is what I was thinking this was what I would have to do.

2003 Toyota Matrix XR
The code came on right after I did this so I am assuming they are related. thanks.

It doesn’t take much to ruin a cat. I toasted mine in about 10 minutes of idling. Been two years though so what’s the rush now? On mine the oil drain plug is a hex bolt whereas the trans drain plug is a square drive that you just use the ratchet on with no socket. Plus its stamped on the pan what it is. You have to try really hard to mix them up but there are books written on the quick lube places doing just that.