Do a search on P0240. I am having the same problem and found a lot of info there. I only have 11,000 miles on my 06 so hard to believe it is the cat already on mine. Going to tinker with it tomorrow.
Howard[dunno]

 

Any more info... i really wanna get this fixxed soon... tired of looking at the cell

 

Adam95GT, if you had used the search functionality of this site you would have found the very first result (besides this thread) is:

http://www.focusfanatics.com/forum/showthread.php?t=165562&highlight=P0420

Which lists possible causes and fixes. More then likely it is either your CAT or an O2 sensor.

 

that code sounds like a bad cat... Is your car having hesitation issues? bogging down a lot? if so your cat is bad.

 

i get the same code about every 2 weeks and I dont have a cat.

 

I know how to search... I was just looking to find out if it was the cat or the 02. the code was off today after being on for a month... it does bog down a bit in between shifts... but other then that the car runs like a champ..

Where can i get a good price on a cat online... i just dont want to drop like $300 on a cat just to find out its an 02 sensor you know what i mean??? What if i swap 02's is that a good way to tell put the number one in the number 2's position and see if i get a different code... that would show the 02 is bad... are they both the same?

 

You can't swap the O2's as the connector is keyed differently to prevent them being connected incorrectly. I've never had to buy a cat online so I can't help ya with that

 

Any way to tell wither its the cat or 02'

 

Cel back on... Still need a cat or 02'... anyone know anywhere im considering buying a header set up.... do the header set ups for the focus replace the cat with a strait down pipe and no cat??? then i can just use or make a mil elim... im still good on imspection for more then a year... and i can always just extend the 02 sensor and weld in a cat later correct?

 

the code says "(bank 1)" which means there is something wrong with your pre cat o2 sensor. it probly went bad. replace it and u will be good to go. and you will get better mpg's

 

bank 2 would mean second o2

 

> bank 2 would mean second o2

I do not believe so.

I believe the bank one and two only is used for "V" or Pancake engines, where you have two heads/exhaust manifolds, e.g., there is no "bank 2" on a Focus.

The P0420 code is referring to the second, not the first, O2 sensor:

http://www.tankota.net/repair/Repair_Manual/03tacoma/di/eg5vzfe/cip0420.pdf

This is for a Toyota Tacoma, but the Common set of OBD-II codes are the same across makes by law.

 

This is correct. the p0420 means that the after cat 02 or the cat is failing the first determines the mixture status...


When im crusing the car seems to kinda be hesitant now... well fell like its struggling kinda bucking/missing a little... but i notice everything... maybe my cat is bad...

 

you could just get a mil eliminator if your prob is just the second 02 sensor

 

Any way to test the 02 sensor test voltage or anything

 

ur right.

 

A narrow band O2 sensor will output between 0V and 1V. If I recall correctly most of the time it hops between the two.

 

Correction... this is the 2nd O2 sensor, so in fact it shouldn't have many cross points. so it should float nicely between 0V and 1V. This is in fact what the computer is looking for to make sure the cat is working correctly.

 

I found a post saying the following:

if your code is about 'bank 1'...
that is before the cat, therefore it is not the cat that is bad.
Does you car have a rough idle?
and when you rev it and it comes back to idle, does it seem to hesitate at 1500-ish
before it drops to 1000 or below?
is your fuel mileage less than normal?
has your water temp changed any? hotter or colder than normal

your most likely culprit is a vacuum leak.
check all of your vacuum lines. (there are only 5 on the svt)
check your pcv valve. make sure it is not clogged
if none of these, check your thermostat. a bad or sticking thermostat can cause
the o2 sensor to freak. because the temp variance will cause the computer to change
the fuel charge.

how many miles does this car have?
if over 80,000 then you should replace your o2 sensors anyway.

I have other ideas as well, if you need more.

just went thru this myself. mine turned out to be the oring behind the master cylinder.
which caused a vacuum leak and bad brakes and the o2 sensor code.





Is it true a Tstat can cause problems with the 02 sensor... i have noticed my fans have been on alot... and my t stat housing cracked a few weeks ago so i changed the housing and the t-stat... i noticed the new one didnt have the burp hole with the giggle pin it had no extra hole in it at all... could this be my problem????

 

Im just looking for a way to narrow down what the problem is....


one quick question:
If it was an 02 sensor wouldnt it throw a nother code as well???

Curently i dont have cash to drop on a 02 sensor and cat... so i wanna figure out what the problem is... also when im crusing at like 35-40 in 4th gear the car kinda vibrates... like it wants to move but doesent. kinda jerks back and 4th and feels like im hitting bumps on the road when im not. im not acceling just holding down the pedal to cruse.

 

> If it was an 02 sensor wouldnt it throw a nother code as well???

No.

The sole purpose of the 2nd O2 sensor is to monitor the function of the cat.

 

Thanks for the heads up man i thought it might throw one of thoes weird closed loop circuit codes or heated 02 codes

 

> Now if the second 02 were to break would it cause a drop in gas milage since it doesent monitor air fuel ratio???

No.

 

> I found a post saying the following: if your code is about 'bank 1'... that is before the cat, therefore it is not the cat that is bad.

That is incorrect.

 

I know this i was wondering if anything after him saying this was worth trusting based on the fact an i4 is a one bank engine. the gas millage is only down about 25-35 miles per tank... is it worth buying an 02 and trying that first.

 

With a drop in fuel economy I would tend to suspect the cat before the O2 sensor as the 2nd sensor has nothing to do with economy. But only a 25-35 mile drop might not be significant enough. IIRC a partially blocked cat will sometimes get very hot (even a bit of glow) after it has been running for awhile at operating temperature. can you take a look at it when it has been running for awhile?

 

That was the first thing i checked no glowing red headers or cat... In the focus when the check engine light comes on does the car go in to retard mode. I know some cars when the check engine light comes on tend to dump fuel and run very rich

 

Picked up an H02 figured for $47 it was worth a try. just took off the old one and replaced it. it was 0EM ford sensor probably original and never changed i got 106k on the car now... I pulled the neg cable to clear the code and drove it like 2 miles to the gas station and filled my tank with 93. cel is currently off... but i havent drove it enough to tell for sure

 

> it was 0EM ford sensor probably original and never changed i got 106k on the car now...

With 106K on the vehicle I would consider replacing the 1st O2 sensor as well . O2 sensors often get slow to respond and inaccurate before the computer senses a failure, and an inaccurate O2 sensor can hurt fuel economy and stress the cat if it is causing the engine to run a bit richer than normal.

 

CEL is back on after 40 miles. Should i take out the new rear 02 and tell them they gave me the wrong one... exchange it for the pre cat one just for better fuel economy.... then buy either a highflow cat or a 421 header?

 

I generally think honesty is the best policy.