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Check Engine Light - P0420 Catalyst Efficiency Below Threshold

I have two older vehicles I drive about about once a week. A 1996 Toyota Tacoma with 180k miles and a 2005 Hyundai Santa Fe with 150k miles. My primary vehicle is a 2017 Toyota Tacoma.

Both my 1996 Tacoma and 2005 Hyundai Santa Fe have had the P0420 (Catalyst Efficiency Below Threshold) code for over 8 months. I’ve cleared the code several times with my OBD2 reader to clear the check engine light, and the CEL usually returns within a week or two.

Replacing the catalytic converter on these vehicles will cost more than the vehicles are worth. I would like to keep the vehicles for a few more years if possible. I haven’t noticed any issues other than the CEL light and the P0420 code. Could driving these vehicles with a possible bad catalytic converter damage the engine? Or is it mostly emissions that are affected? I live in a state where emissions are not tested. I cleared the CEL with the OBDII reader prior to their last state inspection several months ago.

As long as the cats aren’t plugged, no engine damage should occur.

But think of it like this. If the Check Engine lights are always on, how will you know if another problem crops up that could possibly damage the engines?

Go here,, and look up the cats for your vehicles.

They’re not asking an arm and leg for them.


I do check about once a week with the ODB2 reader for any other possible codes.

I thought about universal or aftermarket cats. It could also be some other issue like an O2 sensor. I just don’t want to sink much more money into these two vehicles, but I need a backup vehicle and at this point not sure which will last longer, my 96 Tacoma or 05 Santa Fe. My Santa Fe has had several issues the past few years, mostly electrical problems and power steering fluid leaks.

If there is no risk of damaging the engine by driving the vehicles once a week with the P0420 code and a possible bad cat, then I may just wait a while longer. Otherwise I guess I will look into a universal or after market cat

Then you might want to try this product in one of the vehicles.

I myself have never used it. But it’s a lot cheaper than replacing the cat.

And it might work.