It happened as I was driving home last night 11pm. on a bumpy Michigan road.

This morning I had it checked by:

-Autozone for the engine light- Code p0420

-a local shop and after 1.5 hrs, they told me I needed catalytic converters+o2 sensors. The price was ~ $1600!!!! They reseted the code so all 3 are gone for now. I DID reset my odometer to observe how many miles I'll travel until it comes on again. Will report later

I'm thinking of just going into another shop and have it checked out. I DON'T HAVE $1600. The car feels fine and normal to me.

I called Tuffy and got a quote to replace the TWO o2 DOWNSTREAM sensors. They said $400 total. Denso is the brand. Is this a good price?
I'm obviously gonna have them check it again before I actually get the sensors replaced.

Please help! What should I do?


2001 Toyota 4Runner Limited 4WD 168,000 miles

P0420 Catalyst System Efficiency Below Threshold (Bank 1)
HO2 sensor after the catalytic converter is not responding normally.

1. Check for leaks in the exhaust system between the engine and the cat converter (loose connection, rusted area, or burned out seal)

2. HO2 or A/F ratio sensor before cat converter is bad (remove connector and measure resistance between terminals +B and HT - should be 0.8-1.4 ohms cold). You can find denso or whatever brand you want on ebay, pretty cheap. Then install yourself, even easier. Same for next sensor.

3. HO2 sensor after cat converter is bad (measure resistance as above - should be 11-16 ohms cold).

4. Cat converter is bad.

If you need to replace a sensor, bring your VIN to a Toyota dealer and get the correct part number for your engine. There is only one that works correctly, but at least two available. You don't have to buy the part from Toyota, but you have to have the correct part number. The condition won't damage your vehicle so take your time figuring it out. Good luck!

Most likely either leaky gaskets in the exhaust system,bad o2 sensors or last would be a bad cat.

Check rock auto for the denso replacement 02 sensors and gaskets maybe 150 in parts if you do the labor yourself .

Those prices you listed are insane

Replacing my gas cap fixed it for me.

I tightened my gas car yesterday morning before the shop checked it out and reseted the lights. So far, I drove about 50 miles and 60+mph for 10 minutes straight. The lights haven't come back yet.

I have an appointment on Tuesday and I'll have them check it thoroughly for leaks and sensors.
This shop offers MOTORVAC cleaning and I heard they are good. Do you think that would help?

Also, what if the lights don't come back on in let's say a month? Do I just ignore it then? I haven't noticed anything different or bad in my car.

1. Check for leaks in the exhaust system between the engine and the cat converter (loose connection, rusted area, or burned out seal)

This is what happened to me. Bad muffler. Could hardly hear the small leak.

Most likely going to take longer than 10 minutes. I'm going on 7 months, and mine hasn't come back on.

My muffler rusted off and broke off about 8 months ago. And I got a Walker muffler part+labor for $300. It could be that it wasn't sealed all the way. Idk, I'll let them know but so far, I haven't seen anything leaking.

What have you done so far? and is that the only code you got? P0420?
I read a lot somewhere that it doesn't really affect performance.

Some of my coworkers are saying to get a mechanic to cut off the cats and just put a pipe in there. Bypass it or whatnot. Dunno what the effects of it could be.

I would only listen to your coworkers if you never plan on driving it on the road. It will not pass an inspection without cats. They gave you really bad advise!

I've done nothing to mine. Just cleared the codes.

Lol yep. I don't think there's inspections here in Michigan. Even then, I won't be doing those things to my beloved 4runner.

You need them in Michigan. That's where I bought mine.