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post #1 of 10 (permalink) Old 12-10-2015, 04:10 PM Thread Starter
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Catalyst System Code P0430 Help!

Hey Guys--

I'm driving a 2006 Jeep Commander 3.7L and I had this code come up a few weeks ago and it has remained. After some research, it seems that the problem could be a faulty O2 sensor, which I would prefer to try before changing out the Cat. My issue is I can't nail down which O2 sensor I would need to replace. The code reads:

Catalyst System Efficiency Below Threshold, Bank 2.

As far as I know there are Four O2 sensors on the Commander, does anyone know which one I would be replacing? Also, would I need to drop the exhaust to get to any of them? I haven't had a chance to get under there yet.

Thanks in advance!
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post #2 of 10 (permalink) Old 12-11-2015, 11:16 AM
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OBDII is a federally mandated protocol that all cars engine controllers must use. It mandates that the engine controller must monitor the engine and emissions system for proper function that would effect emissions and do periodic tests on the emission equipment.

OBDII mandates a test of the Catalytic Converter and to set a code if it fails the test. That is the code you have, one of your two Catalytic Converters has failed the test. Bank 2 usually means the right bank, from the perspective you sitting in the driver seat, i.e. the right Catalytic Converter from that perspective.

Chrysler, and just about all vehicle, have an O2 sensor in the exhaust to sense what the Air/Fuel ratio is, the amount of O2 in the exhaust is directly proportional to the A/F ratio. This is how the engine controller keeps emissions down and gets better fuel economy.

The way Chrysler, and few others, test the Catalytic Converter to tell if it is working correctly, is to install a 2nd O2 sensor in the exhaust after the Catalytic Converter. The engine controller then compares the O2 sensor outputs from the exhaust before and after the Catalytic Converter. If the Catalytic Converter is doing its job correctly, it will cause by-products in the exhaust to chemically combine to more inert compounds. These by-products chemically combining will consume oxygen in the exhaust and the exhaust coming out of the Catalytic Converter will have less oxygen than goes in. Thus the output of the O2 sensors should be different. If the output of the O2 sensors is the same, then the Catalytic Converter must NOT be consuming any oxygen, i.e. NOT working at all, and thus it fails the test and lights the code.

So, its possible bad O2 sensors might be giving the engine controller bad information to make it wrongly assume the Catalytic Converter is bad. But think about the probabilities.
  • If an O2 sensor goes bad, it should trip a code for a bad O2 sensor. Although it is possible for an O2 sensor to be out of calibration or bad and NOT trip a code.
  • The Catalytic Converter only fails the test if both the before and after O2 sensor output is the same. What are the chances an O2 sensor goes bad or off calibration just right to match the output of the other O2 sensor?
Its possible, but NOT likely its a bad O2 sensor, either upstream (before) or downstream (after) O2 sensor could be bad (but failed in a way to NOT set a code and also match the other sensor output). You have 2 O2 sensors per bank. So Bank 1 says the O2 sensors and the Catalytic Converter are good, a quick test to confirm if it is or isn't the O2 sensor is to swap the O2 sensors from Bank 2 to Bank 1. If it was one of the O2 sensors, then Bank 2 Catalytic Converter would pass the test and turn off the code, but now Bank 1 Catalytic Converter would fail the test and turn on the code for that. If the Bank 2 Catalytic Converter still fails the test and Bank 1 still passes the test, then it can't be the O2 sensors.

In short, swap both sensors to opposite side, if the problem follows the sensors to the other side, its the sensors. If the problem remains on the same side with the known good sensors, then the problem has to be the Catalytic Converter. It takes several hours of driving if NOT several days before the engine controller runs the test. I would Clear the Codes before driving with the swapped sensors, i.e. reset the PCM by pulling the battery cable for an hour.

Its NOT so quick, those sensors seize in the exhaust from heat and can be a bear to get out, NOT to mention they need a 20+mm wrench that typicall is NOT in most folks tool box.

I have NOT looked up part numbers for the Commanders O2 sensors, but usually vehicles multiple O2 sensors use all the same O2 sensors, they only differ by the length of the pig tail, cause they are different locations, which would make it a different part number.

Remember, the Upstream O2 sensor is used for feedback to manage the engine A/F ratio, you have one for each bank on the engine. The Downstream O2 sensor is just to test the Catalytic Converter, also using the Upstream O2 sensor, you have one per Catalytic Converter. Since you have 1 Catalytic Converter per bank, you also have one Downstream O2 sensor per bank. Since the Downstream O2 sensor is farther away from the engine (and engine controller) it typically has a longer pigtail to the wire harness.
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post #3 of 10 (permalink) Old 12-11-2015, 11:28 AM
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The Upstream O2 sensor's output is vital to maintaining a proper A/F ratio, if it is off calibration from age and use, the engine will have the wrong A/F ratio, and thus NOT making as much power as it should, less mileage and more pollution. Some folks replace the Upstream O2 sensor periodically just to ensure the engine is running in tip top shape. Like at 75k or 100k miles. Its a bit of overkill, cause if the O2 sensor gets off calibration enough to make a real effect, the PCM "SHOULD" catch it and set a code for a bad O2 sensor, or a code for something effected by the O2 sensor.

The Downstream doesn't do anything but test the Catalytic Converter, there is NO reason to change that unless it truly goes bad.

Also keep in mind, there are a lot of aftermarket O2 sensors that are NOT as quality as the OEM sensor, nor calibrated as well for your particular vehicle. Especially the Commander, there has been posts about aftermarket universal or even specific sensors causing problems in the Commander.

So, if you want to buy a new sensor and put it in, you could argue replacing the upstream sensor isn't a waste, the engine likely will run a bit better with a fresh upstream O2 sensor. Provided its a sensor that is as good as the old sensor you're taking out, i.e. most folks will only use the OEM sensor from the Dealer. Downstream sensor, you may be wasting your money and time, it really doesn't do anything but test the Catalytic converter and thus there is nothing to be gained in putting in a fresh one if the catalytic converter is passing its test.
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post #4 of 10 (permalink) Old 12-11-2015, 11:41 AM
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Oh, one more thing to look at. An exhaust leak will cause O2 to be sucked into the exhaust and throw off the O2 sensors, well NOT throw them off, they are correctly reporting the elevated level of O2 in the exhaust. BUT, the PCM NOT knowing the extra O2 is from an exhaust leak, will logically conclude it is a bad A/F ratio or failed tests, etc....

Again, possible, but NOT likely. It is at least worth a look over of the exhaust for any cracks or leaks, leaks between the head and exhaust manifold or at any joint is a common spot for leaks.

Remember, a foot or two after the catalytic converter and especially in the muffler or farther down, the pressure surges even out and is just always overpressure, no reverse, so oxygen can't get sucked into the exhaust after those points, nor get up to the O2 sensors to throw them off.
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post #5 of 10 (permalink) Old 12-14-2015, 07:22 PM Thread Starter
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Thank you for all the Great Info Mongo-- I appreciate that! Based on that advice, I have definitely determined that it is the Passenger side (Bank 2 ) catalytic converter. So now I am ready to replace, but the only direct fit I can find would require me to replace the whole cat system (including the Bank 1 Cat and other tubing, which looks fine). Since I don't have a welder, is there any way for me to just purchase an aftermarket universal Cat (which I am finding for about $100 or so) only and just swap that in for the bad one? Would I be ok to cut the old one out and just swap the new one in using exhaust clamps, or is this something that has to be welded?

I really don't want to purchase the whole Cat setup to replace, but since they are relatively cheap ($400 or so for everything direct fit) if that is the route I have to go, I will do that. Just looking to see if its possible to replace only the bad cat before I go that route.

Thanks!
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post #6 of 10 (permalink) Old 12-14-2015, 08:51 PM
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First, your options depend on where you live. California and New York you have no option, you can only replace emission parts with Dealership OEM parts. I believe they check them on inspection and will reject you if it does NOT have the OEM part number. I did see the dual CAT pipe setup from a mail order Dealer that supply parts at a discount for $1069 but likely will charge a lot for S&H.

Some states may also have laws about universal cats and modifying exhaust and Cats with clamped in universals, they may or may NOT enforce those laws with inspections.

The right side CAT does NOT look to have a lot of straight pipe after the CAT, it may have trouble clamping an universal CAT in and even welding it in if you're NOT a professional welder. Also do your homework, there are different types of CAT's, three way, two way, those with air injection, etc. Although I think three way that catalyzes CO, HC and NOx have been in use on all cars for 20 years, so likely a universal will be the right type.

Here's the thing, if you can get the universal in and fit without leaking, it might NOT last very long. It should work for a while, a year or two, most of the universals are lower quality than the direct fit. The universals aren't built for the temps or flow or amount of exhaust that might be pumped through them. I could be wrong and the universal can handle the load just fine and it might last another decade.

I don't envy you, its NOT an easy decision, I see a direct replacement pipe with everything for $400 on Napa Online. It might be worth it to just bite the bullet and get the correct part that will work right the first time.

At the same time, you're going to have to pull the old pipe and toss it away anyway. So you're risking a hundred bucks if it doesn't work. I've seen the universals for $75, but by the time you get claps, adpaters, cut it out, etc, you'll easy be up to $100.

Last edited by Mongo; 12-14-2015 at 08:54 PM.
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post #7 of 10 (permalink) Old 12-14-2015, 09:13 PM Thread Starter
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All good points Mongo. I am in North Carolina so the Emissions testing is not nearly as Strict as California or NY. I am going to get under the Truck tomorrow and just check everything out one more time. I remember when I purchased the truck last year, the previous owner stated they had the Catalytic Converter just done recently (I didn't get much more detail that that) but I'm wondering if so would that be somehow covered under warranty as it was definitely less than 2 years ago. However, I don't have any paperwork and am now in a different state, so I don't see that being an option.

I most likely will just buy the entire direct fit assembly just to get it over with, but if you have any other ideas I would appreciate it!
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post #8 of 10 (permalink) Old 01-07-2016, 11:25 AM Thread Starter
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So I finally received the entire new Cat System from Eastern (its the Eco II direct fit model). I knew I would either have to reuse or purchase new Flange bolts as they were not included, but I was under the assumption that the gaskets were included, which they are not. I am having a heck of a time figuring out which gaskets I need, and If I need 3 (for the 3 connections) or just one for main pipe? Do anyone have any experience with this and knows which gaskets I need?

Thanks in advance!
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post #9 of 10 (permalink) Old 01-11-2016, 02:00 PM Thread Starter
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Anyone?? I've asked many different sources and no one can seem to give me an answer!
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post #10 of 10 (permalink) Old 01-13-2016, 03:00 PM Thread Starter
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Well if anyone is reading this, I decided to skip the replacement and try the Spark plug anti-fouler trick on the Bank 2 cat-- and low and behold it worked. I cleared the code, and just got it inspected no problem. I realize this isn't a long term solution but I am selling this Commander and upgrading to a newer V8 or Hemi model, so I just really needed to get this inspected. Thanks to those that helped!
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