after about 40 miles worth of driving, the CEL comes on. i have no idea what this code means.

 

i have absolutely no idea, i am simply taking a shot in the dark here so PLEASE CORRECT ME IF I AM WRONG!!! just from the sound of it, i would think its an o2 sensor throwing the code, witch would lead me to believe its running rich or its time for a new set of catalytic converters.... i have no proof to back this up, this is just my reasoning after reading the description.

 

Its impossible to know without knowing that codes your truck is setting. I don't know that it would be a O2 sensor or not as you should set a code long before 40 miles since you would have been at optimum operating temp long before that point. Same goes for the cat. Besides that, the code such as this should be perm. until it is reset. If you start your truck & it isn't on immediately, it isn't a perm code.

 

Even though this is for a Scion, it might help:

http://www.myjdmphoenix.com/images/0...efficiency.pdf

Try Googling this: "P0420 Catalyst System Efficiency Below Threshold (Bank 1) ford"

 

it stays on until i reset it, then about 40 miles later it comes back on again. 40 miles total. i can drive like 25, then wait 3 days and drive another 15 and it'll come on.

 

I'm going to have to agree. There are O2 sensors fore and aft of the converters that measure efficiency of those converters. Likely gonna be the converters are getting ready to be replaced. Definitely need to verify, though.....

 

In that case, it could be an O2 or cat. in that your car will need a certain amount of miles before it has verified that you have an issue. Like was posted though, check the codes. Take it to Autozone & they will check your codes for free. Good luck & let us know what it turns out to be,

 

i figured it would be the o2 or the cats. i replaced one the day after i got the truck and have the other 3 sitting around waiting for a day above 40* and with under a foot of snow...

if its the cats, what will running as is do?

 

can you see the picture?

 

If they're not stopped up? You will be single handedly responsible for destroying the ozone layer. And the PCM will start trying to adjust the fuel/air mixture to compensate, so fuel mileage and performance may suffer a bit.

If they ARE stopped up? You'll notice a power drop off and other odd occurences starting to pop up. An air pump can't pump air if it can't get what is pumped in pumped out so that it can pump more in.......

And now that I have thoroughly muddied up the whole thing.....

(and I can see the pic, don't know about Mish, but it's pretty plain to me.)

 

Your profile picture? Yes, I can see that. Nothing else though.

 

I can see the picture which is why I gave you data on code P0420.

 

Mish - this is the code and definition ^^^^

 

The code is the result of the PCM detecting the 'excess' switching of the rear OX sensor in bank 1.
It is telling you the cat is not performing it's original function within specs. Not normally a sensor fault since the sensors have their own fault codes for detection.
Here is how the 'CAT MONITORS" work.
The PCM looks at the 'RATIO' of switching between the front and the rear OX sensors as a way to tell the condition of the cat in that bank.
If the ratio goes out of programmed limits, the cat is said to be failing.
Clearing the code naturally will take some time for the PCM to look at it again and reset the code. It won't go away until the condition is cleared. EPA mandated! as a requirement to be accepted for sale of the vehichle.
Cat is contaminated, blocked, broken or has been over heated or any combination of the above..
Rare that a sensor is falsely reporting a cat issue unless it is electrical harness short or a ground but even then the reporting code is different.
There are over 1000 codes that have almost everything broken down and covered specific.

 

First thing first. Don't automatically think the Cat is gone. When this type of code appears, it's beyond a "backyard" mechanic diagnosis. You don't want to throw good money at bad and replace the cats and it turned out to be a sensor or wiring issue.

The code is telling you that the sensor Bank 1 Stream 2, downstream of the cat (after), is reading out of Spec. There is a posibiltiy that the upstream sensor is bad, causing a rich mixture on one bank or the other. Thus causing the downstream sensor to read out of bounds also.

What needs to be done at your local garage or Dealer, is they can drive the vehicle and monitor what each O2 sensor is doing in real time. Also they can see is it's also a wiring issue. They will let you know for sure if it's the sensors or the cat. My hunch is the sensor. If it was the cat, there would be a greater issue of driveability.

Lastly, O2 Sensors are a lot like spark plugs. They don't last forever. They only have a service life of about 60,000 miles (100,000 kms) Thus, they will wear out even if there is nothing wrong with your cats.

I have a 2002 Supercrew with 145,000 Kms. I have already replaced 2 of them.