2008 Mountaineer- with P0430 code | Ford Explorer Forums - Serious Explorations

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2008 Mountaineer- with P0430 code


New Member
March 17, 2014
Reaction score
City, State
Yuba-Sutter, California
Year, Model & Trim Level
2007 Mercury Mountaineer
Greeting from Northern California's Yuba-Sutter region.

I'm new to the forum... on my second EX/Mounty. Found the forums several weeks ago when looking up info about Catalytic Converters.

CEL on prompted a stop at the shop we use, where a quick scan pulled up Catalytic Converter related codes. The CEL was reset and I was advised to bring it back if it came on again.

It did. I'm now advised that it's putting up "P0430 Bank 2 cat efficiency" codes.

The shop recommends replacing the Catalytic Converters, advising "The rear oxygen sensor is switching the same as the front oxygen sensor indicating that the catalytic converter is faulty."

I'm trying to make sure I really DO need to replace the Cats.

If so, to ensure that the shop has identified and fixed any problems that caused the need for replacement.

Here's vehicle details:

2008 Mercury Mountaineer
131,176 Miles
Assembled in Louisville, KY in Nov. 2007.

I've spent the last couple of hours checking the posts related to P0430 codes... none seem to be for this generation of EX/MNT.

Looking for info on whether this is any kind of common occurrence for this generation, and details.

Also what I should be asking that the shop checked and how to get them to dig further if it seems like the situation got a once-over-lightly approach to diagnosis.

A few suggestions on how to put that out without pissing of the techs involved would also be welcome.

Feel free to ask about any potential symptoms that I might have overlooked.

A post about P0430 codes being traced to alternators leaking AC into the DC circuitry and creating some false triggers raised an eyebrow.

Generally been quite happy as a 96 Explorer LTD 4.0 V6/4WD owner from 99-2009 —41,000 to more than 225,000 before it began to reach nickle-and-dime territory. Which prompted me to search again and buy the 2008 Mountaineer in 1009 with 40,100 miles.

Love the ride. People remark how quiet it is. Zips along and hauls a 5x8 cargo trailer cross-country without complaint. (My wallet would love better MPG, but I'm not driving slow, either.) Been running Goodyear Fortera TripleTreds in New England Snow and Southwestern desert.

Only major problem was a transmission issue at around 65,000 on the return leg of a cross country trip. The Ford dealer could either dig into the tranny and fix... with only a 12mo/12K mile warranty or replace with Ford remanufactured trans. and 36 mo/36K mile warranty for about $3.1K. Went with the remanufactured tranny, although I would like to have known what caused the tranny to begin leaking fluid approaching Little Rock, AR. Smoke from the fluid dripping on the exhaust tipped me to the problem quickly.

Otherwise a happy Mountaineer owner prepping for a trip to Vegas and back. (NAB)

That's it for now. Thanks in advance for suggestions. Welcome to spring!


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Thanks much. Added some information that is helpful in understanding what I was being advised.

IE: The O2 sensors were switching at the same rate, indicating that the Cat wasn't working.

Other info I've been reading indicates that the engine-side O2 sensor switches at a relatively high rate, and the tail-pipe O2 sensor should be switching at a comparatively low rate if the Cat is working.

Would be interested in knowing the average life-span of the cat. converters used in the 2008 models. And whether there were any regularly seen potential causes of cat. failure.

Again thanks!

I don't know the life of a cat what i've seen is people dismounting the test pipe and soaking the cats in water with a lot of soap some say it works some say it doesn't but i guess it's worth to try instead of paying big bucks for new ones

My truck started throwing the same CEL code about 6mos after I replaced plugs and coils. I brought it to my mechanic who is pretty well versed in Ford vehicles. He said to fill up with premium full, run a couple bottles of injector cleaner and go on several long drives on the highway. I filled up with 91 octane, used a couple bottles of regane (gumout) and went on a couple of long drives. The CEL actually went off after about 50 miles. After two tanks of this, I've gone back to regular gas with no cleaner. It's been a month and about 1000 miles. CEL remained off. No idea what it was but my mech says he sees this quite often with Fords. Who knows.

He said to fill up with premium full, run a couple bottles of injector cleaner and go on several long drives on the highway. I filled up with 91 octane, used a couple bottles of regane (gumout) and went on a couple of long drives.

Thanks t0. That's something to try.

I may take my 99-year old Dad for a drive on Saturday. Depends on whether the shop can actually determine why my brakes aren't working the way I'd expect... after $353.56 in new calipers, new pads a d new rotors. But that's another thread.

Cheers from North of Sacramento.


Time to revive this thread....

I get the same P0430 code in my 2006 Explorer 4.6l, I have the issues narrowed down I believe.
I have run two bottles of Catalytic Converter Cleaner ($25 a bottle) claimed to be one of the better ones out there. After a 9 hour, 700 mile trip at 65 mph average, the light remained out. I thought all was good in the land of warning lamps and faulty sensors!
Then, after arriving at my destination, checking in at the hotel, we drove around town for the evening and after a bit- the light came on again!! So, it's only low speed, or local driving that sets the light off.
Maybe the O2 sensors are bad and can't heat up or work at low efficiency? Or can the cats be bad?
Hopefully this helps pinpoint the issue?
Anyone else have suggestions or solved the P0430 I describe??

You have the 4.6L engine, are your exhaust manifolds leaking when the engine is cold??