Addressing some common misnomers of the P0420 code

Just had this light pop on… yay

 

I have had this P0420 code for awhile. I have a 2005 regular cab 2.7 4cylinder 4wd tacoma. It came on three weeks after I had my spark plugs changed with NGK iridiums. Truck still ran ok for about six months but eventually developed a misfire/loss of power type feeling. Took it to shop mechanic pulled plugs and they were shot with roughly 18000 miles. Now mechanic says I need new catalytic converters and he thinks I need a new fuel pump because its running lean and fouling plugs. He already changed front O2 sensor and he says it passed fuel pressure test but still thinks fuel pump is bad because I have 266666 miles and have never had pump changed. May have to give in and go to dealership and hope they know whats wrong.

 

Caligula, is there a voltage range that should be seen with the scan tool when looking at said O2 sensors? Let's say a 2003 3.4L V6, at temp and running live data. What should be expected to be seen on the bank 1 sensor, and the bank 2 sensor? I have been trying to track down the actual oem spec for this scenario and have been coming up short.

 

wow I'd get a second on all that.

I just washed my cat cause I can and replaced the o2 (which I think is still good so I kept it) on my p0420
Held for 1000+/- then now every 3 or 4 days just driving to the job site. Never back so I'm thinking a misfire or something from closed loop to open or, is that backwards, after she warms up in the chilly mornings. Hooked up Torque and yep that's when it happens. Now to trace that but still gettin 20mpg on my last fill up.

 

Interesting thread and lots of info. My .02 and experience.
Have had the 420 code three times on my truck. About every 100k. Solution each time has been a new gasket on the junction before the cat. It breaks down and allows ambient air into the system. 324K with original Cats and O2 sensors.

Edit
Mistyped. After second cat before second O2 sensor

 

grntruck, can you be more specific about that location of the bad gasket that pops the P0420 code, in your case? Are you talking about the flanged junction located after the first (front) cat, but before the second (rear) cat? Or somewhere before the first (front) cat?

 

Flange after the second cat, before the second O2 sensor.

 

Thanks for that reply

For what it's worth, my 2.7 was pulling a lone, intermittent P0420 for awhile, which, over a few months, became more frequent.

Turns out, I found an exhaust leak at the flange joint between the two cats. I ordered a $12 gasket for it, but in the meantime, slopped some Muffler Weld all around the flange joint to seal the leak - then cleared the code, performed the required drive cycles afterward, and just passed CA smog with flying colors this morning.

It buys time, and keeps me on the road legally until I can get to the gasket repair. 320K-ish miles, both original cats, and so far, $2000 richer. Hoping that's the end of it. The thing simply will not die

 

Just a recap on my p0420. It was a bad thermostat. It was stuck open. Replaced and haven't had the code pop since. Realized that my truck was taking to long to warm up.

 

Lots of good 420 insight in this thread! Might revisit my 420 code I’m still dealing with on my 3.4l now. Yay!

 

Great info in this thread. Thanks to all. I have a few months to chase my p0420 code before I need to smog. I'll look at the simpler stuff first. My cats are aftermarkets put in about 150,000 ago. Have 401,000 now and the truck runs great other than that dang code.

 

Read somewhere about using a shop vac to find exhaust leaks. Worked! I cut out a round piece of foam to fit snug in the tail pipe, then cut a hole in the center using the shop vac hose as template. Used the vac in the blow vs. Suck mode. Then used soapy water in a spray bottle to wet the flange junctions. Leaks confirmed at both flanges. Used rtv and so far so good, no more cel.

 

I did a similar method but used a bicycle tube cut down with a shop vac! Worked pretty decent and found a few pinholes that I welded up. Still got a pesky 420 code :/ really do not want to pay for new cats. Tossing new exhaust manifold gaskets on next, will report back

 

I wish I found this before I started trying to fix the problem a couple years ago. First a cleared the code and it stayed gone for a couple months. Then I cleared again and it came back right after I started the truck up. Then I bought an ebay Cat replacement kit and new O2 sensors.... But damn was it hard to remove that aged/rusted bolts up top of them converters. Had to use a blow torch and angle grinder. then I ended up just getting an entire MBRP exhaust since I was going through all the trouble already.

I fell for all the post about reduced MPG and could cause power loss etc so I just replaced everything.

great information.

 

Not a reply but a question..... Could it be that my catalytic converter needs to be replaced?. I only have 490,000 or so miles on it.....

 

Just replaced the downstream O2 sensor with a Denso. Next day drove 500 miles from Sacramento to San Diego and the CEL has stayed off.

 

Did OP get banned ?

 

aaaaaand it’s back..

 

Pain. Sorry to hear that.

 

I've been chasing this on my truck with 208k miles for the past year. I recently replaced the rear O2 but the code came back after a few weeks. I also have been fighting an exhaust leak at the header to cat connection, but that one is currently sealed. I connected an air compressor on low pressure to the tail pipe using this: https://amzn.to/48odQmY

I haven't found any obvious exhaust leaks, but it definitely sounds like I have one at certain RPMs while driving. I'm hoping there's not a crack on the collector of my LCE header. I will try to see if I can get some soapy water in there and an inspection camera at the same time.