Think I may need to replace Catalytic Converter on my 2003 Taco

After that check the wires, a broken or partially broken wire can false your signal.

 

Just checked the upstream o2 sensor and it shows 1.3 ohms. Is that normal or is it because that o2 sensor is really not an o2 sensor and its an air fuel ratio sensor and can't be tested using a multimeter or does the 1.3 ohms mean it is bad and I need a new one?

 

Anyone know? Lol

 

Hey OP,

Here is a conclusive test that should get you closer.

Step 1. Locate o2 sensor, run engine until it reaches normal operating temp

Step 2 unplug o2 sensor put the positive lead from your meter on it then the Negative to the battery, set the meter for 12VDC

Step 3 note the readings. Voltage should fluctuate between .40 and .60 volts RAPIDLY
If it is slow or does not fluctuate at all, replace the sensor.

If all tests out good, look at the manifold, they crack, if all is good, then cat replacement is in the works.

Helpful?

 

If it wasn't helpful to the OP, it sure was to me. I've been looking for that procedure off and on for a week.

That should be a sticky.

Thanx!

 

Anytime,
Was looking for it yesterday... had to dig through all the notes I’ve made over the years.

 

Step 2 tell me how you do that at the same time. The leads aren't that long.

 

I suppose a jumper. This is good simple info. for all of us who don't use meters much.

 

Like a bunch of other people have said now. P0420 can mean a lot of things, and bad cats is one of the least likely (if you still have stock cats). That rear flange looks troublesome, thats where mine finally failed this year. Looks like someone tried to fix it at some point or something. P0420 also doesn't necessarily mean bad O2 sensors, you should get a separate code for that. However, if there is a leak then it's hard for the computer to tell whether or not the O2 sensors are good. Here's a couple videos for I found helpful, hopefully you do too.

https://www.youtube.com/watch?v=N-exs1iMLFU&t=679s
https://www.youtube.com/watch?v=NKsS6AELPuM

 

There is an exhaust leak on this flange. I noticed someone tried to fix this when my last exhaust pipe was replaced with what looks like some sort of U bolt. Is there a simple fix for this or will this require me to cut off the Cat flange and weld a new flange then getting a new gasket and then bolt the exahust and cat flanges together? I am not a welder so that is not an option to do it myself? How much would a shop charge to do this as well? Thanks.

 

A good small welding shop shouldn’t charge more than $100 I would think. Or you could see if you have any friends that can weld. I just did this same thing on my truck the other week and I am by no means a “great” welder, but hey it holds and there’s no leaks.

 

Those flange bolts loosened. You need to take that apart, toss the old gasket and get a new one. They are $6 from AutoZone.

Clean up the flange face, new bolts and gasket and I bet your 420 code goes away.

 

Nah look at the actual flange, it’s all deformed, tightening it more probably wont fix it. I had the same problem. Even tried one of those bolt on flange fixers and it didn’t work cause the actual flange was bent, rusted, and wasn’t sealing well.

 

Shouldn't the deformed flange be the same size as the exhaust flange?

 

It’s the same size yes. But the metal is not uniformly thick anymore due to rust. Therefore you’re having trouble getting even pressure on the gasket causing a leak somewhere. A new gasket is a good place to start since they’re cheap and you’ll need one no matter what. But I think you’ll find that when you unbolt the the flange is gonna fall apart more. You want to have to relatively flat and smooth mating surfaces for the gasket to sit on.

 

That flange is shot, no way it'll seal for long anyway. I haven't asked in years and years but muffler shops used to not carry any flanges because of the wide variance.

as an aside: why isn't there a pipe standard for exhaust? A little late now but it has been a expensive headache to match into a system.

 

https://www.summitracing.com/search...t&SortOrder=Ascending&N=4294948820+4294872621

Enter the pipe diameter, take measurements of the other flange to make sure the holes will line up. Then find one that is the right size, buy it, and take it to a muffler shop, or to a welder.

 

Thinking of trying this. What do you think? Using a split flange with spring bolts and a new gasket.

 

Still gonna have an exhaust leak.

I think you would be further ahead by taking everything apart and beating that flange flat. With a hammer.

 

Yeah don’t think that’s gonna work either, I tried something similar. Leak was still there. Even pressure and a flat mating surface are super important.

Has anyone on here though about putting an o2 sensor bung before the flange?? That would eliminate this oh so common problem of leaky flanges causing codes and failed inspections...