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P0420 fault code----HELP!!!

C

chrisjohnson72

CEG'er
Joined
Feb 26, 2007
Messages
49
Location
Plano, TX
I have posted multiple threads with multiple fault codes. I have successfully treated each one and a new one keeps coming up.

Latest fault code is P0420.

Here is what I have done so far in correcting previous codes. I have a 98 Contour SE V6 DOHC w/200116 miles.

Replaced EGR Valve
Replaced EGR Sensor
Cleaned EGR passages
Replaced both O2 Sensors before the Cats
Replaced PCV Valve
Cleaned Throttle Body

The code has something to do with my cats being bad, however, I have seen other posts regarding to adding Mileliminators to the O2 Sensors? I am 4 months past inspection and can't get the darn CEL to stay off long enough to get it inspected. The guy at autozone said I probably have a vaccuum leak??? Could this be correct? Would adding Mileliminators to the O2 Sensors allow me to pass inspection? Is it very difficult to install these? Also, my air filter cover is missing several clips to hold it down tight? Could this cause a fault code? I am at wits end and love this car and want to keep it rolling. My apologies for peppering you with questions, but this is the authority for this car!!! :)
 
you just need to install 2 mil eliminators. I assume since people can pass inspection with headers, that you will be able to pass with bad precats. You just have to get rid of the check engine light.
 
chrisjohnson72 said:
For clarification....Do I put them on the 2 o2 sensors BEFORE the cats? or the 2 after the cats?
Click to expand...

After (at the bottom). It is for the lower O2 sensors.

If you are looking from the front, for Radiator side (Bank 2) O2 sensors, it is the one on the right (furthest from the Oil filter).

If you are looking at the firewall side (Bank 1), it is the one at the lowest point. The highest one on Bank 1 Firewall side is the one detailed on the Duratec Maintenance -Read First how to by GoldenTour.

Once again, you want to install for the lower O2 sensors (for Bank 1 P0420 and Bank 2 P0430).
 
Would you recommend replacing these 2 o2 sensors as well when I do this? I have already replaced the 2 O2 Sensors that are before the cats.
 
chrisjohnson72 said:
Would you recommend replacing these 2 o2 sensors as well when I do this? I have already replaced the 2 O2 Sensors that are before the cats.
Click to expand...

They replace the sensors, no new sensors needed.

If the pre-cats are original, they probably are bad. This is not a big deal unless they cause exhaust backpressure. The main cat can handle the job once it warms up.
 
Hi,
If you do a search then you'll see that the dreaded P0420 code is kinda common.
I'll leave it as an exercise to the reader (always wanted to type that in!) to read about MIL eliminators, EPROM re-flashes by the dealer etc. etc.
MY SOLUTION -- if you want to get this thing to pass emissions/inspection and not have the CEL come on for a long time is:

i) Buy a can of Berryman's B12 or Seafoam (preferably B12 coz Seafoam smokes like a mother!)
ii) Get your hands on a nice long, flexible straw or length of not-too-thick vacuum hose)
iii) Remove one of the (two) black upper vacuum hose-connections that are on the TOP of the engine. You can't miss them -- they're right beside each other and are in line with the air-intake/MAF area.
iv) Insert one end of the hose/straw into the UIM (upper intake manifold) by way of the 'hole-connection' .
v) Start the car - and don't be too upset if it idles very low or stutters. If it stalls and just won't start - then just 'pinch' the hose/straw a smide by using e.g. a paper binder-clip. Then it'll start.
vi) Slowly introduce the other end of the straw/hose into the can of B12 and let the engine 'sip' the liquid contents. It'll take a good 5 minutes for all the liquid to be 'sipped' - so make yourself comfortable.
vii) When all the B12 is gone - take out the straw/hose and re-insert the proper vacuum connector into the UIM - just like it's supposed to be.
(As you are doing this - the engine may stall -- no biggie.)

vii) If your (check engine light) CEL is on - then clear it with a code-scanner or disconnect the +ve battery terminal (for at least 1 minute).

viii) Re-connect the battery terminal if you've removed it.

ix) Start the engine and keep your foot off the accelerator. She may idle low and stumble a bit -- but after a short period of time - she'll settle down.

x) Now go drive the car for a couple of days - letting the car completely cool down each time. (This gets all the 'readiness monitors' to go to 'set'. If you have a code scanner you can verify this. If you don't then you can get the Autozone dudes to check for you.)

If everything is copasetic -- go get your car tested/inspected.

The CEL - P0420 code may or may not come on for 6 months or more having done this 'fix'.

Been there, done that, it works like a charm.

BTW, 'numerically speaking' - and I've SEEN this with my own code scanner. The downstream oxygen sensor for bank 2 is the 'snitch' that causes P0420. It should be reporting a nice consistent .75 of a volt (or higher/better) for the CEL to NOT go on. Trouble starts when this voltage starts to go lower (.6) and the CEL can be triggered when it gets REAL low e.g. .5 or .4V. (The other bank i.e. downstream 1 - always seems to be a nice .75V -- go figure).

After you've done the Berryman's B12 fandango - - both downstream oxygen sensors are 'back up' to .8 (and sometimes .9) -- which keeps the ECM happy and convinced that everything is OK in emissions-land.



Gerry
 
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