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Discussion Starter · #1 · (Edited)
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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Replacing the downstream O2 sensors will NEVER fix a 420/430. Failed sensors will store other codes. Possible the upstream sensor is lazy or contaminated causing chemical shift, but the most likely cause is a failing cat. If the cat isnt broken up and causing excessive back pressure, the easy fix are some "MIL Eliminators" sold by many online stores including Amazon and Ebay for around $20 a pair. Simply remove the downstream sensor, screw in the device, and screw the sensor into the device. They work.
 

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I'd change the bank#2 upstream (pre-cat) o2 sensor which is the easiest of the 4 to access right behind the radiator. If no success, then consider mil eliminator or cat.
 

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Discussion Starter · #4 ·
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.
 

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I'd change the bank#2 upstream (pre-cat) o2 sensor which is the easiest of the 4 to access right behind the radiator. If no success, then consider mil eliminator or cat.
So, bank 2 is the front of car cylinders? I always though that bank 1 was front of car and bank 2 was firewall side. Please confirm.
Thanks, Bill
 

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Bank#1- firewall. Bank#2- radiator. Bank#1 is whichever bank cylinder #1 resides...
Thanks, back in the day (20 yrs ago) I probably had all that kind of gen info in my brain, I haven't worked a hi-pro parts counter / machine shop since then. Now medical/ nursing crap in my head and my family.
So, what is the layout of this engine and firing order since we're on that topic now?
Thanks Bill.
 

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Discussion Starter · #9 ·
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.
 

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Discussion Starter · #12 ·
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 :(
 

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Discussion Starter · #13 ·
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.
 

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Discussion Starter · #14 ·

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Discussion Starter · #15 ·
Update:

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?
 

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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.
 

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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.
Can confirm MIL Eliminators do work.
 

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^^^^ As can I :)
 
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Discussion Starter · #19 ·
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.
 

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I've been going through the exact same situation for some time. Just been clearing the code when it pops up. It's been off for a good while but I now have an annoying metallic vibration/rattle after cold start. I've heard the same noise on other cars I have owned and it is coming from inside the cat. Went to Ebay to get the best price I could find, $207 and change for an OEM Ford cat, $7 and change for an OEM Ford manifold gasket. Picked up the lower gasket from Vato Zone (Auto Zone here in Texas) for a few dollars. Will update after the job is done, probably this coming weekend.
 
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