2K Tacoma TRD P0420 Dilemma

I was looking for a site like this for a while and glad I found it. I hope to get the much needed help as this P0420 code has me going nutzzz!

Vehicle: 2000 TRD Taco
Miles: 213k
Automatic

So, recently purchased the truck from an older gentleman. Immediately after driving it home, the CEL came on with p0300 l, p0301, p0304 and p0306 codes for misfires. Did complete tune up (ngk plugs, wires, pcv valve and replaxed a potentially bad coil on cyl 1), light was still on. I then only got a p0301 misfire code and it ended up being a bad fuel injector on cyl 1. Replaced it and the truck ran like new and CEL was gone.

Well.... 2 days later after driving about 30-40 miles, I got the CEL back on and this time it gave me a P0420 code (catalyst low threshold bank 1). Read that it may be the o2 sensors or worse the cat. Well decided to start with the least expensive. Live data was showing sensors fluctuating as follows:
B1S1 at 3.254 -3.325
B1S2 at 0.00- 900

So I did the Cataclean bottle and 60 miles later CEL still on, replaced both o2 sensors with Densos and CEL still there...I have had very good luck with cataclean before but doesn't seem this time it's gonna work. I'm just stumped as to how the p0420 came on now and never before along with the other issues. Last thing I'm looking to try as I also read, this could cause a p0420 code is replacing the temp coolant sensor (one communicating with ECU) and the temp sensor for the gauge as the gauge itself never worked (always at the very bottom) UNLESS there is something else I'm missing to check out and you guys can help point it out before I assume it has a bad catalytic converter. I'm in California so I am really dreading this being the issue as you all know how expensive they are here due to CARB specific applications.

Anyhow, I know it's a long post but really hoping you all can help a fellow taco owner out.

P.S...I/M readiness was all green checkmark indicating all monitors were good to go for smog so wondering how that would be if it were to have a bad cat?

Blessings!

 

Anyone?

 

Exhaust leaks would be the only other thing. Most likely need cats.

Were the 02 sensors replaced with Denso units?

 

After the sensor replacement I went ahead and cleared the CEL manually with the obd2 scanner and so far 100 miles in and the CEL hasn't come back on but now waiting on the EVAP and CAT monitors to clear I order to call it a fix.

 

Misfires can damage the cats, so It's not surprising. At 215k new cats are almost certainly in your future.

 

Update, monitors all cleared after 110 miles. Taking it to smog tomorrow!

 

what did you do, anything different from your last post?

 

Nothing, I just drive as I normally would

 

I have been dealing with a P0420 code on my 97 Tacoma 2.4L 5speed for over a year, so far based on Toyota Forums have replaced EGR valve and EGR module all vacuum lines and air flow module next to charcoal canister, and at least 4 treatments of Cataclean, with no change, reading this post looks like need to get out from under hood and move to exhaust underneath, truck has 166456 miles, my code reader only showing P0420 code nothing else. SUGGESTIONS?

 

The rear sensor is not seeing enough difference from the front sensor.

Check for exhaust leaks between sensors.

 

Update: took to smog and passed. Problem apparently solved.

One thing i did differently from other times I've had CELs is that I manually cleared the code after the o2 replacement as usually I'd wait for it to clear on itself. You may want to do that and see if it comes back on as some CELs apparently don't clear unless you do it manually after problem or faulty parts removed.

Keep in mind though, your monitors will be incomplete again until monitors clear and may require extensive driving, mine have always cleared within 100 miles.