0420 code

True......but many 2000’s were 2 cats ( California standards ) also , I’ve got a 2000 that was purchased new on the east coast and it came with California emissions. It took me awhile to figure out why the 2000 Tacoma 49 state replacement front O2 sensor didn’t work properly.

 

yeah I think the year 2000 was when they switched over to CA emissions standards on all Tacomas, or maybe it was partway through the 2000 model year. But 01+ should all be 2 cats/50 state emissions

 

If I replace the o2/af sensors and the cats are bad, will it destroy the sensors? They have almost 200k miles on them and will need to be replaced any ways. I was considering replacing them first and seeing if it’s the problem, if not then deal with the welded on cats

 

Bank 1 reads upstream so no problem there , like you say 200,000 miles it’s probably tired by now any way. Try that one first.

P.S.
On my tired 20 year old cats, first I replaced both O2 sensors, the check engine light on went from bad to worse, then took out the new downstream sensor and that cured the light problem for a year. (The old rear lazy sensor helped.) Eventually the light on problem came back. Did the $4. capacitor & resistor trick and now the light is off again....how long ? We’ll see.

 

do what matchew1776 is telling you to do or get the URD rear O2 sensor simulator... you can "fix" it for under $100.

 

When I had this code it ended up being a bad front cat. I replaced that and then both o2 sensors a little later because of bad fuel trims. This has actually fixed the problem and made my truck run better than ever. If you go with a simulator or resistor it’s not actually fixing the problem...more like putting a bad aid on it.

 

That’s what I’m thinking too. I don’t want to do something just to make the light go off. My truck a year ago had good amount of power. I now can hardly go 60 up any sort of hill on the highway. It’s has lost at least 40% of its power so something is wrong

 

A clogged/bad cat can do that. And a bad upstream O2 sensor can cause the cat to go bad

 

I replaced the A/F and O2 Sensors. I figured they needed to be replaced anyways and they are the cheaper option so I started there. I reset the CEL and it hasn't come back on. Power has been slightly better but not what I would expect it to be. The previous owner (who I now know lied about almost everything) put in a new A/F sensor at some point because the gasket was almost new. The O2 sensor was original though. He also put on cheap cats so I'm guessing they still may be bad. Unfortunately he went the cheap route and got weld on ones. So if the CEL comes back on I am going to redo the whole exhaust with the walker bolt on exhaust for around $600.

Also I joyously found a large amount of rust on the frame that I did not see when I bought it. I looked at the frame pretty well but didn't stick my fingers in any holes (haha) in the frame. Well under the rear body mounts I decided to do so and found that it is extremely rusted...took a hammer to it and its almost mush. So that will be a new project this summer. I may cut the rusted sections out and weld in new ones or just brace it. I should have known after I took the bed cover out (that he claimed he put in to protect the bed) and found two large holes in the corners. Hoping to make the truck last 10 more years but I'm guessing that's wishful thinking.

 

My buddy’s 02 double cab kept throwing the 0420 code and after we spent too much time diagnosing, he finally took it to a reputable exhaust shop and they confirmed it was the rear cat causing the code.

I have a walker front cat and Pace Setter rear cat with OBX headers and they haven’t thrown any codes since installing them about a year ago.