Dreaded P0420 help.

[jedi_jackson]

My 2005 Liberty 2.4L has started throwing the P0420 code. Runs fine. It will only do it when I ride about 30-45 minutes. Short trips out won't come on. I can clear the code and it will stay off until I drive 30-45 minutes. I had replaced the front O2 sensor when I first got the Jeep because of another code. I recently removed the exhaust from the manifold and the cat looked good, with no obvious problems. I pulled the rear O2 sensor and it didn't look bad either. Checked the temp in front of the cat after driving and at rear and noted about a 50 degree cooler temp at the back of the cat. When checking the O2 sensors on a code scanner, the front O2 sensor reads anywhere from 0.075 to 0.780 at idle or running around 2000 rpm. The rear at idle reads 0.745 to 0.780 but then at 2000 rpm it goes from about 0.075 to 0.780 and not smoothly, pretty quickly. So I'm thinking my cat is probably bad, what do you guys think? Also thought about trying a non fouler for the rear O2 sensor. If so what size?

 

[adamkrz]

I always thought the leaving temp of the cat should be hotter.

 

[jedi_jackson]

I always thought the leaving temp of the cat should be hotter.

I was thinking that too, which is why I'm leaning toward the cat being bad.

 

[Bikeflyer]

The cat if shot by a laser themometer it should be really hot at the outlet regardless of the inlet -+. Thats how the Sensor spacer adapters work, like a filter capacitor of the heat. I replaced my cats and couldn't get the computer happy since they were californias before and I dont have a fortune to get anything but generic. Adding sensor spacers was enough to get it over the edge to proper. Heads up if you plan to replace them, check your label to see if they are the same.

 

[mercdudecbr600]

P0420 is lazy cat response, basically need a new cat due to reduced efficiency. Try sensor spacer trick first.

 

[Johnny O]

Might have an O2/O3 test off the tailpipe done if available in your area…

 

[jedi_jackson]

Might have an O2/O3 test off the tailpipe done if available in your area…

I don't know if anyone local so does that unfortunately. Think I'm going to try the spacer first and then go from there. Thanks!

 

[XWrench3]

well, this is interesting. i had no idea about sensor spacers. where do you get them? is it a common part that most auto parts stores carry?

 

[Bikeflyer]

Ebay is usually the source for that. In a parts store you will get the "spark plug de-fouler" item. The ebay ones I have now are a little more purpose built with a mesh inside that stabilizes temperature a little better. Look to pay 25-30 each.

 

[Okok]

My 2005 Liberty 2.4L has started throwing the P0420 code. Runs fine. It will only do it when I ride about 30-45 minutes. Short trips out won't come on. I can clear the code and it will stay off until I drive 30-45 minutes. I had replaced the front O2 sensor when I first got the Jeep because of another code. I recently removed the exhaust from the manifold and the cat looked good, with no obvious problems. I pulled the rear O2 sensor and it didn't look bad either. Checked the temp in front of the cat after driving and at rear and noted about a 50 degree cooler temp at the back of the cat. When checking the O2 sensors on a code scanner, the front O2 sensor reads anywhere from 0.075 to 0.780 at idle or running around 2000 rpm. The rear at idle reads 0.745 to 0.780 but then at 2000 rpm it goes from about 0.075 to 0.780 and not smoothly, pretty quickly. So I'm thinking my cat is probably bad, what do you guys think? Also thought about trying a non fouler for the rear O2 sensor. If so what size?

There is a product called cataclean you can get at most auto parts stores that claims to clean your cat if you’re looking to find band-aids. Can’t speak to its efficacy, but it might be worth a shot.

 

[Johnny O]

There is a product called cataclean you can get at most auto parts stores that claims to clean your cat if you’re looking to find band-aids. Can’t speak to its efficacy, but it might be worth a shot.

It’s a scam. Mostly methanol.

the Techron is proven in The 3.7 V6

 

[Johnny O]

It really isn’t possible to clean a catalytic converter. I’m not at work so Ill skip the chemistry lecture on how one works. Feel free to Google the chemistry

most, if not all of the time it’s deposit s on the sensors or failed sensors due to lake of preventative maintenance or improper fuel that throw these codes. Unless it took an impact or has holes in it, the cat converter is the last thing to replace.

start with the Techron. Pay attention to the fuel you are using (owners manual states 87 for a reason) make sure you have the proper NGK plugs gapped to .040 and don’t get scammed by that platinum plug sales pitch.

bad fuel operation is going to throw soot and lower temps that prevent proper reactions, as are leaks.

platinum is the universal nitrogenous catalyst at around 800F, those scam cleaners evaporate and are converted to water long before they get to the honey comb.

treat the problem at the source: **** combustion and it’s sticky, high pH products.

Techron used properly in conjunction with proper plugs, air and oil, and good contact on the COPs, plus the right fuel are key here.

 

[Okok]

It really isn’t possible to clean a catalytic converter. I’m not at work so Ill skip the chemistry lecture on how one works. Feel free to Google the chemistry

most, if not all of the time it’s deposit s on the sensors or failed sensors due to lake of preventative maintenance or improper fuel that throw these codes. Unless it took an impact or has holes in it, the cat converter is the last thing to replace.

start with the Techron. Pay attention to the fuel you are using (owners manual states 87 for a reason) make sure you have the proper NGK plugs gapped to .040 and don’t get scammed by that platinum plug sales pitch.

bad fuel operation is going to throw soot and lower temps that prevent proper reactions, as are leaks.

platinum is the universal nitrogenous catalyst at around 800F, those scam cleaners evaporate and are converted to water long before they get to the honey comb.

treat the problem at the source: **** combustion and it’s sticky, high pH products.

Techron used properly in conjunction with proper plugs, air and oil, and good contact on the COPs, plus the right fuel are key here.

Uhm, telling this guy to go back in time and take better care isn’t really helpful. Sometimes you’re broke and need to improvise.

 

[mercdudecbr600]

It really isn’t possible to clean a catalytic converter. I’m not at work so Ill skip the chemistry lecture on how one works. Feel free to Google the chemistry

most, if not all of the time it’s deposit s on the sensors or failed sensors due to lake of preventative maintenance or improper fuel that throw these codes. Unless it took an impact or has holes in it, the cat converter is the last thing to replace.

start with the Techron. Pay attention to the fuel you are using (owners manual states 87 for a reason) make sure you have the proper NGK plugs gapped to .040 and don’t get scammed by that platinum plug sales pitch.

bad fuel operation is going to throw soot and lower temps that prevent proper reactions, as are leaks.

platinum is the universal nitrogenous catalyst at around 800F, those scam cleaners evaporate and are converted to water long before they get to the honey comb.

treat the problem at the source: **** combustion and it’s sticky, high pH products.

Techron used properly in conjunction with proper plugs, air and oil, and good contact on the COPs, plus the right fuel are key here.

Ya I’ve tried replacing rear o2 Sensors on p0420 codes, they don’t help. Doesn’t hurt either

 

[Ksat]

I wouldn't bother using temps to diagnose converter problems. It's never really an accurate way to do it Visually inspecting an O2 will also do little to tell you whether it is functioning within normal parameters. The vast majority of below threshold codes are (unfortunately) the result of the cat's reduced efficiency. Though rare, I have heard an exhaust leak post upstream O2 could maybe cause it, too If you don't have a leak, look at a graph of both the upstream and downstream O2 voltage outputs at the same time, if your scanner supports that. If the waveforms look more or less identical to each other, the cat is bad. Here is a very good video which discusses this:

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Some people have reported that soaking a converter in a soap and water solution can revive them, that is of course given the internal honeycomb structure is still intact. There are a number of youtube vids from some fairly reputable sources that talk about it, if you want to look it up. Products that you pour into your gas tank that claim to clean a converter without having to remove it I would treat as more suspect.

 

[jedi_jackson]

I did try to soak the converter in soap and water and I used duralube catalytic converter cleaner too and still getting the code after those. The honeycomb in the converter looked intact and didn't appear clogged.

 

[SWilliams]

It isn't that they get clogged it is that the catalyst materials get coated with oil/fuel residue and that causes them to slow down or stop working. The solvent wash sometimes will clean that off enough that they work again, but unless the issue upstream is repaired it will be a short lived repair. The issue with the spacers is that you can then get a code for slow O2 response because the idea with them is that the system tests the operation of the cats and the O2 sensors in a similar way, it will drive the system rich for X time, then lean for X time and monitor the gases out of the converter as well as the amount of time the rear O2 takes to see those changes. If the rear O2 takes longer you get a code.
Overall the true repair is cat replacement as well as any repairs needed upstream to make the replacement last. For me in NY it gets $$$$$ real fast as I am limited to OE or CARB approved parts. Any time you thing the units on the Jeeps are bad, price some of the ones on newer GMs... Just put one on a 2016 and it was over $1100.00 for the front set up..