P0430 Catalytic Converter Question

[campbmic]

Hey all! I have a 2008 Pathfinder with 140k miles on it. I have a CEL which is throwing code P0430 (Catalyst System Efficiency Below Threshold Bank 2). I also have a rattling under the truck, which I think is coming from the exhaust system. It sounds like a bearing bouncing around in the exhaust.

Before I buy a replacement catalytic converter I wanted to make 100% sure that was the issue and not the O2 sensor. I've had an O2 sensor fail before and there was no rattling sound.

Can anyone tell me if a rattling sound is common for a failed catalytic converter? Thanks!

P.S. Are the catalytic converters the same for both sides? Or do I need to specifically get a "Bank 2" one? Is bank 2 on the driver or passenger side? Thanks again!

[smj999smj]

Most of the converters that trigger codes are due to the substrate become inefficient and not being able to break down the exhaust gases, anymore. The majority of these cases don't create a mechanical issue or restriction issues and some can be remedied by installing a spacer or "CEL elminator" on the rear oxygen sensor (this will often keep the code from triggering, but may not pass your state's inspection, so be warned if you do this). If that's not an option, replace the incident upstream converter is the fix and most converter supplies will require proof of replacement of the oxygen sensors with the installation of the new converter to uphold the converter's warranty. However, if the insides of the converter are making noise, it's definitely time to replace! With the variable valve timing being used to accomplish EGR, the potential exists for the engine to ingest bits of substrate into the cylinders where it will score the cylinder walls. That said, there are other things that can cause noise on the exhaust and most of the time it's a heat shield that is the cause (I'm actually getting ready to fix a shield on my Pathfinder in a few minutes). If you don't know where it's coming from, take a plastic or rubber mallet and bang on the exhaust in multiple areas until the source can be isolated and identified.
In regards to the oxygen sensor causing the catalyst codes, it's possible, but most of the time you will get oxygen sensor codes to trigger, as well. If one or more is not operating properly, the ECM will usually see that and set the code.

[campbmic]

Thanks for the reply!

When you say "replace the incident upstream" rather than use the spacer, do you mean replace the catalytic converter?

I took a rubber hammer to the exhaust and all the heat shields seem to be secure, nothing moved around or made the noise I hear when the truck is on. Also the noise seems to dissipate when the revs go up. When the engine goes back to idle the noise seems to start back up.

The noise sounds like someone shaking a spray paint can, or like a bad bearing. When a catalytic converter goes bad is there typically a noise it makes?

I'm charging up the ipad to get a video of it, so Ill post that soon.

Thanks again for the help!

[campbmic]

Also, about a month ago I had an issue with a blown fuse that made the car tun over but not start. I turned the car over a lot trying to trouble shoot it. Then about a week after that I had a misfire in a cylinder. I drove the truck for awhile like that and found the issue was a bad coil, which I replaced. Im not sure if these issues could cause any damage to the cat or not, but figured Id mention them.

[campbmic]

We had the passenger rear cat replaced 2 months ago. Its still under warranty so I took it to the shop that did the work. They said the P0430 code means the driver front cat is bad.

They said that if the driver rear cat was bad it would not throw a CEL.

They said the rattling noise is coming from further down in the exhaust. Its coming from the "box" where the two sides of the exhaust meet. They said there is some debris rattling around in there (probably from when the cat died).

They suggest replacing both front and back driver side cats. Then $100 to take the exhaust off and remove the debris. They said there is a chance its a coupling or something else rattling but it sounds like its coming from the "box".

I'm confident I can replace both cats and remove the exhaust myself to do the work. I'm just trying to figure out if I should replace both cats or just the front. If the front cat did break apart could the debris be sent back through the second cat into the "box"?

Or is it more likely the 2nd cat (back) failed and sent the debris into the "box" and its just showing as a failure in the 1st cat?

Is it true that only the front cats can throw a CEL?

[dawgn86]

I got both the P0420 and P0430 on my 2006 PF.

I put the spacers on the rear O2 sensors and the codes went away for a few months, but came back. I put a new O2 sensor on the downstream driver side, but still have the codes.

Looking into some Walker replacements now.

[CRC11007]

My '05 threw both of those codes at about 120K miles. I bought the Walker replacements off RockAuto (I believe there was a promotion at the time), and paid my shop a couple hundred to install them. No codes since, and given the risk of the deteriorating material getting sucked back in the cylinder and causing damage, it was money well spent. 30k miles later, still no codes.

[smj999smj]

Thanks for the reply!

When you say "replace the incident upstream" rather than use the spacer, do you mean replace the catalytic converter?

I took a rubber hammer to the exhaust and all the heat shields seem to be secure, nothing moved around or made the noise I hear when the truck is on. Also the noise seems to dissipate when the revs go up. When the engine goes back to idle the noise seems to start back up.

The noise sounds like someone shaking a spray paint can, or like a bad bearing. When a catalytic converter goes bad is there typically a noise it makes?

I'm charging up the ipad to get a video of it, so Ill post that soon.

Thanks again for the help!

Yes, I meant the incident catalytic converter. The noise will be a rattle coming from the inside of the converter shell.

Many upstream converters on these vehicles seem to fail right after a misfire condition, especially those due to a failed coil. The coil fails and allows unburned fuel to enter the exhaust stream, into the upstream converter. Next thing you know, catalyst codes trigger.

The ECM triggers catalyst codes based on the response from the upstream and downstream oxygen sensors. Since the downstream catalytic converters are located AFTER the rear oxygen sensor, they are not monitored and can only cause catalyst codes if they are clogged, which is not impossible, but rare. I eliminated my downstream converters, replacing them with Doug Thorley mid-pipes. Technically these are for "off-road" use, as it is considered as "tampering with a federally controlled emission device," but it passes inspection where I live (it may not pass in other areas or states, however, especially California or NY State).

Debris from the upstream converter will not end up behind the downstream converter, unless the downstream converter is gutted (someone removed the catalyst substrate from inside the converter). The debris in the "box" (which I assume is what they are calling the "Y" junction of the front pipes to the single pipe that goes into the main muffler) could be from the driver's side, downstream converter. Obviously, the only way to know what is rattling inside the "box" is to disassemble the exhaust and inspect it. As far as the downstream converters, you can't inspect the rear side of the substrate unless you have an endoscopic camera. One could simply hold the converter/pipe assembly and tap it on a hard surface to see if any debris falls out of it. The front side can be inspected, which would catch any debris from the upstream converter. If you're replacing the upstream converter, you have to remove the downstream converter, anyway. I can see the shop's view point, however. Since you've already have replaced the passenger side, downstream converter, and currently need to remove the driver's side, downstream converter in order to replace the driver's upstream converter, it would seem like a good idea to replace the downstream driver's converter, as well. It's not a bad and for them it covers their butt in case you decide to not replace the downstream converter and end up with problems later on with it. Again, as a reminder, make sure you read the converter's warranty; most will require replacement of the oxygen sensors to uphold it in the case where it needs to be replaced within the warranty period.