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P0430 - "CAT Efficiency Below Threshold, Bank 2"

46107 Views 30 Replies 10 Participants Last post by  CDsDontBurn
I've got that error, and had it for a while already. I've had it on my other vehicles before as well, and the fix has always been to replace the downstream o2 sensors. Well, I did that a few weeks ago on my Taurus and changed both downstream o2 sensors (replaced with Motorcraft units) even though only one was bad. Why, you ask? Because my train of thought is to "replace it in pairs". Since getting to the rear o2 sensor's pig-tail harness was quite an adventure which required removal of the upper intake manifold, I decided to replace all 6 spark plugs (replaced with Motorcraft platinums) as well because removing the intake manifold is part of the same job to replace the spark plugs. I wrap everything back up, clear the code, and go on for a 65 mile drive, ~50mi on highway, and ~15mi on surface streets. The code stays off and I'm a happy camper. This was about 3 weeks ago.

Fast forward to just this past Tuesday and I get another CEL. I get out my ODB-II scanner, and I'm surprised to get the P0430 code again.

Reading online what some people have experienced when getting this code, symptoms vary from nothing noticeable aside from the CEL being on, loss of fuel efficiency, to misfires, and very sluggish performance. My experiences seem to be just the CEL being on. Some people have said they've needed to replace their CAT while other's have just needed to replace the o2 sensors. And here's where my confusion is. Some people replaced the pre-CAT o2 sensors and others have replaced the downstream o2 sensors (like I did). Some people replaced the CAT all together.

What troubleshooting do I need to do to figure out what it is that I need to fix? Some have suggested to swap the o2 sensors around. Some have said to replace the upstream sensors. Those are good ideas which I could try, but what else is there for me to try?
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I'll try replacing the upstream sensor then and report back what happens.

I did clear the code when I got the CEL again. Since it had been about 3 weeks or so from when I replaced the o2 sensor to when the CEL came back on, I'm not sure how long it will be before the CEL comes back on, if it even comes back on. I suspect it will, however.

As for the MIL eliminators, I'm in California. While that may work for the time being, I'm not sure how it will be impacted come time for the smog check in about 2 years as here in California, cars older than 5 years (so on their 6th year IIRC) cars are required to be smogged. Though, the car will not be put up on the sniffer (that's for cars 1999 and older), they still hook up the car's ODB-II port to a scanner and run an emissions system check. I'm not sure if the MIL eliminators would cause the emissions system to report back something that it shouldn't.
CEL went off earlier this week on its own. I'm a little tight on cash right now so I don't know exactly when I can fix it. RockAuto has the FoMoCo o2 sensor for $95. There's a Denso brand (which I trust as a brand) available for $72. Would you guys get the Denso brand o2 sensor or stick with FoMoCo on this?

Bank#1- firewall. Bank#2- radiator. Bank#1 is whichever bank cylinder #1 resides...
Standing at the front of the car with hood open: cylinders l to r bank#1 (firewall) are 1-2-3. L to r bank#2 (radiator) are 4-5-6. Firing order is 1-4-2-5-3-6.
Good to know! For those of us that need a visual, I'm borrowing this from Rock Auto....

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ALL narrow band O2 sensors operate by the same chemistry. the only difference between any O2 sensors is the electrical connector and the length of the wires. Any brand is fine.... Bosch (who first produced them back in the 1970s), Denso, NGK, NTK, etc. If I remember correctly Morotcraft are rebadged NGK.
Good to know! I'll look for NGK and price shop.

Have you considered a propane test before replacing anything? Please see this link for testing instructions for the O2 sensors and catalytic converter with P0430.
Never knew of this. I've never had to troubleshoot o2 sensors before outside of just replacing them to fix a problem! Reading this though.....I don't have a live scan tool :(
It's been a while since I've posted. The light has been coming off and on still, however, the light is remaining on for longer periods of time now. I'm looking up on ordering replacement o2 sensors as I've decided to replace both front sensors. Why? Replace in pairs, is why. I'll do some price shopping, and if I order online, I won't have them until sometime early or mid-week next week. If I decide to just pull the trigger and buy at a store, I'll do the job this weekend.
Rear o2 sensor is a PITA to get to, but it came off real easy once I got to it. The funny part is that the front o2 sensor is right there, but it was a PITA to get off. Hopefully, this fixes the issue. Otherwise, I'll have troubleshooting to do and hopefully I don't have a bad CAT(s).



I've since also done the pre-CAT o2 sensors as well because the CEL came back on after having done the trailing o2 sensors. The CEL went away and had remained off for some time after having done so.

Sometime mid last week, the CEL came back and when I checked it, it was the same CEL code, P0430.

What do I do now?
What do I do now?
As I stated earlier in this thread, replacing the post cat sensors will NEVER cure a 430/420. Failed post cat sensors will set a DIFFERENT code. Post cat sensors often last the life of the car.

Example: A year ago my adult daughters 85K mile 13 Limited threw a 420. She has an extended warranty. She took it to the Ford dealer. Some moron who should never be allowed to open the hood of a car replaced the bank 1 post cat O2. I told her the CEL would come on in a day or 2. She stated that the dealer said the car was fixed. Guess who was right. Hint: I was not the dealer. The dealer ended up replacing the bank 1 cat with no deductable after I told the service manager that the tech who diagnosed the problem as a bad sensor didnt have a clue.

The "MIL Eliminators" will keep the CEL off allow you to pass smog. If the car is visually inspected on a lift, an astute inspector may notice the eliminators. Years ago when we had visual inspections along with a tailpipe sniffer test here in SE WI, and the inspectors didnt know an EGR valve from a fuel injector, and passed everything unless you pulled in with a 8-71 Roots blower sticking up 2 feet out of your hood.
So replace the CAT is what you're saying.

Sorry for not having re-read through this thread.
Still haven't done the fix on this. The CEL keeps going off and turning on by itself. Money has been tight which is why the delay on my fixing this. I found a website that sells OEM Ford parts for cheap, so when I'm ready to buy both sets of CATs, I'll get them from there. $210/ea+ shipping, so it's doable....just not quite now for me. I know the issue can turn into something more costly, but I hope it can last a few more months. I'll DIY the fix myself though, so that'll save who knows how many hundreds of dollars when the time comes.

Finished the front CAT replacement last weekend. Pretty straightforward job. Only hiccup was the lower flange studs. They are low grade (8.8 metric/grade 5 standard). Crimp nuts stripped one on removal and one of the new ones on install.

Here's a pic of the original CAT inlet:

And the new one:

After seeing the condition of the original CAT, I am going to replace the other side, against the firewall, but am not looking forward to that job.
Wow! what a big difference! But I'm surprised that just a little bit of fuzz would make such a big deal for the code to pop up. Were you able to discern how thick the honeycomb is? And it's hard to tell in the pic, but is the CAT element plugged up? If it is plugged up, and now that you have the new one on, have you noticed any performance improvements or increase in MPGs?

I have the a 4 code problem p0171 p0174 p0430 and p1450 I have the vehicle at the Ford Shop and they are quoting me just south of $500 to fix this and still be on the hook for a $750 Cat conv. if problem reoccurs. so possibly a $1250 with replaced cat con and the following. Should I bite the bullet and get it fixed by them the following is the breakdown, the diagnostics of ($129) and do the vapor management valve installed ($129.33) clean throttle body($185) and reprogram powertrain control module($75.08) or just pay the $130 and do it all by ourselves? emphasis on the WE lmao
For the $500 ballpark figure, what are they going to do to "fix" the problem if they're not replacing the CAT? Or is that $500 + $750 for the CAT for a total of $1250 to do the job?

See if the $129 diagnostic fee can be applied to the cost of the repair. Cleaning the throttle body should be an easy task of just a few bolts and some carb cleaner / brake cleaner.

Why do they need to reprogram the PCM?
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I'm finally getting around to this and am in the process of installing the exhaust manifold bolts. But key information I don't know is, what are the exhaust manifold bolt torque specs?

Currently I have them installed finger tight +1/4 turn by ratchet.


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^^ $575. That's how much the pair of CATs cost from the dealership. I was unable to buy them online at the much lower price of $213 and $207 for whatever the reason may be. One vendor had a dumb policy of "we can only ship to your 'ship-to' address if you buy through PayPal" I gave them the middle finger on that and told them I'd buy elsewhere for more money if they didn't accept my VISA as payment, which I did. I bought front and back because I'm of the type of mentality that "If one is bad, the other one probably isn't too far behind".

Anyway, I found the answer to my question above with torque specs on the CATs / manifold. 18lbs on the nuts.

Also, I'm not sure why Ford didn't just use bolts instead of studs for removing the manifolds. I had two of the studs come off on the rear head when I removed the original CAT. It was rather annoying to have to separate the stud from the nut and then reinstall just the stud before being able to continue. BTW, the studs are 5mm.


Pictures of the old CATs

Front: https://photos.app.goo.gl/jxnDem6BoVHBjFkY8

Rear: https://photos.app.goo.gl/upSmi8VVr4deAFxk6

The front one just had buildup of stuff. The rear one had damaged honeycomb material. I'm not sure exactly why P0430 is considered "failed" if it looks fine? I guess the car's ECU knows best, right?

All said and done, the job was relatively straight forward. The rear CAT was a little more difficult to work with as about 95% of that part of the job was under the car. I had to remove the upper intake manifold to reach a few of the bolts and the primary o2 sensor removal. Unless anyone here knows of an easier way to access that top end hardware for the next person that needs to do this, that is what I did to make that part of the job happen.

I also ended up replacing the air filter because it looked pretty dirty.


And the car now has 99,2xx miles and the cabin filter has never been replaced. Yea, I replaced it as well, lol. The old one was rather disgusting!

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It's just shy of a week and the car has been driving code free!
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I have a new, and related, issue. Thread linked below:

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