Think cats are clogged need opinions.

[Bigshawn]

My 01 yukon 5.3 has 334,000 miles and P0430 and P0420 codes are both coming up but it doesn't feel like they are clogged. I've ran some techron and cataclean thru it about 10k miles ago but didn't help with codes. I'm afraid of dumping to much money into it with the miles that are on it but it's still running strong. I looked on rockauto and can get new cats plus the 4 o2 sensors for like 300 to 400. What do you guys think? @Tonyrodz always value your opinion

 

[OR VietVet]

IMO, the codes may be related to the sensors and I would do all 4 of them first. How old are the existing sensors? Do yourself a favor and use GM or Delphi sensors.

 

[exp500]

And a Vacuum gage on a test drive will verify Cats.

 

[Fless]

Have you looked at the graphs of the O₂ sensors' activity? I would agree with @PNW VietVet to check and/or replace those first.

How about fuel trims, short- and long-term; have those been looked at? The upstream (front) O₂ sensors will drive the fuel trims. The downstream (rear) ones will drive the cat efficiency codes.

 

[George B]

I have been down this road before. I ended up doing a parts shotgun. Four sensors and new cats got me another 100k on a 2003 Burb. That is from 156k to 256k before I traded it off.

 

[Fless]

It would be best, from my point of view, to do some diagnostics to confirm before you spend the $$ on cats. O₂ sensors are somewhat a wear item and will likely need to be replaced at some point, anyway. To each his own, though.

 

[George B]

I should add that I agree with @Fless and @PNW VietVet about diagnostics. I did a fair share of checking how the cats were performing prior to biting the bullet.

 

[Bigshawn]

@PNW VietVet they are still the stock o2 sensors and @Fless yeah i have been keeping a eye on them. The 2 front ones work ok but the 2 downstream quit reading. One of them was like 8 months ago and the other just quit like 2 months ago but if I remember right the one would work here and there but it just mimicked whatever the front one would say. I know that means something just can't remember lol. I got like 25k saved to get a newer vehicle but I want to get everything out of this one and I got alot of new parts on her. I forgot to say earlier p0401 code just started coming up to which is egr insufficient flow. That's kind of what was making me think the cats and o2 sensors maybe are both going out.

 

[OR VietVet]

Again, IMO, at the minimum replace all 4 sensors with quality parts. If they are the original sensors, they are way past due for replacement.

 

[Bigshawn]

Sorry my Wifi is acting up, man it ****** me off. Ltft on both sides usually runs between 5 and 8.

 

[Bigshawn]

Ok well i hoping they come out easy. I'll get 4 new o2 sensors and clean my egr valve to see if it's that helps. I appreciate it fellas. Now one more question when I was younger my friend had a tiburon and the cat clogged on it and his exhaust manifold was cherry red. I could use a infrared temperature gun just to check and see if they are getting hot right?

 

[swathdiver]

My 01 yukon 5.3 has 334,000 miles and P0430 and P0420 codes are both coming up but it doesn't feel like they are clogged. I've ran some techron and cataclean thru it about 10k miles ago but didn't help with codes. I'm afraid of dumping to much money into it with the miles that are on it but it's still running strong. I looked on rockauto and can get new cats plus the 4 o2 sensors for like 300 to 400. What do you guys think? @Tonyrodz always value your opinion

Trust your instruments, the computer has determined that the cats are no good. If the O2 sensors were no good, they have their own codes. Be very wary of Chicom cats, they do not last, not even a little while. They don't have to be clogged to be bad btw.

 

[Fless]

Trust your instruments, the computer has determined that the cats are no good. If the O2 sensors were no good, they have their own codes. Be very wary of Chicom cats, they do not last, not even a little while. They don't have to be clogged to be bad btw.

If the O₂ sensors are not up to the job, you can't trust the instruments that rely on their validity. I'd say do the O₂ sensors and the EGR work and see what happens. If it comes to new cats, so be it. But the pain of replacing cats these days is not insignificant, especially when not needed.

 

[Bigshawn]

Trust your instruments, the computer has determined that the cats are no good. If the O2 sensors were no good, they have their own codes. Be very wary of Chicom cats, they do not last, not even a little while. They don't have to be clogged to be bad btw.

That's what I was thinking too but you guys are much smarter than me when it comes to most of this. Is Davico a ok brand. I think I'm going to try the o2 sensors first but if they start giving me trouble and not moving cause alot of stuff here in PA loves gets nice and rusted tight. I think i might just order new cats that way everything goes together easier. Unless someone lives near Carlisle, PA and wants to make some money lol.

 

[swathdiver]

If the O₂ sensors are not up to the job, you can't trust the instruments that rely on their validity. I'd say do the O₂ sensors and the EGR work and see what happens. If it comes to new cats, so be it. But the pain of replacing cats these days is not insignificant, especially when not needed.

I have to disagree to a point. If the sensors are not up to the job, the computer will throw codes for them as well. In my experience, even a lazy sensor that's on its way out can still detect a bad cat. On the other hand, given the age of the vehicle and with more time than money, it's not a big deal to put in new sensors first just to see. My experience has always been though, that if those codes are thrown, the cats are no good.

 

[OR VietVet]

Possible causes of a P420 and P430 codes can be the sensors as well as the cats. If the sensors are it, they are less expensive than the cats, especially if you stay away from Chicom cats. If the cats are bad, you would want to do the sensors anyway. Spray some good penetrant on the sensor threads and let sit and then a couple more times before attempting to break loose and use a socket or box end wrench and not an open end wrench. May have to heat them as well. With the miles on the rig, I would bet the cats should be replaced too but the less expensive initial repair is the sensors. I don't envy you at all if the parts are exposed to salt.

 

[Tonyrodz]

I agree with the consensus here. Def do the O2's first. Pa is just like NJ with the rust and salt, so be prepared to strip some threads and maybe you'll need to replace some of those O2 bungs. Had to do both of my rear O2's and it was a nightmare. I like Denso sensors, they're really good parts. I'm contemplating doing this on my Express van. I just might try to hollow out 2 of my cats. There's 3 of them. Good luck and keep us updated.

 

[Bigshawn]

Possible causes of a P420 and P430 codes can be the sensors as well as the cats. If the sensors are it, they are less expensive than the cats, especially if you stay away from Chicom cats. If the cats are bad, you would want to do the sensors anyway. Spray some good penetrant on the sensor threads and let sit and then a couple more times before attempting to break loose and use a socket or box end wrench and not an open end wrench. May have to heat them as well. With the miles on the rig, I would bet the cats should be replaced too but the less expensive initial repair is the sensors. I don't envy you at all if the parts are exposed to salt.

Yep been in salt it's whole life. The body and frame are not bad at all but when it comes to getting parts off i usually got use a mini sledge or map gas. Alot of *********** oil and if that doesn't work heat plus a breaker bar.

 

[rockola1971]

When a cat gets clogged, the easiest way to diagnose it is start vehicle up and get up to operating temp. Then hit the front of the cat with a IR Thermal gun and then do the rear. Compare the temps. If the front is substantially warmer than the rear then the cat is clogged. When a cat is clogged they typically glow red/orange so have a look at them at night while engine is running. The vehicle usually runs like crap too.

 

[OR VietVet]

If it is salted/rusted enough, I would just resign yourself to likely doing cats as well and figure in for any broken attaching bolts and don't forget any gaskets that me be needed. If you do the penetrant, use Aero Kroil. Best I have ever used. I used it a lot when I ran shops on salty roads in KC, Mo.