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buschman
Anonymous Poster
billsrepair.co5623@sbcglobal.net
Mar 10, 2008, 11:40 AM
Post #1 of 4
(3074 views)
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emission test failed
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i forgot to mention that the failure code was po420, test type obd11, thanks, that was on the 2000 ford contour.
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DanD
Veteran
/ Moderator
Mar 10, 2008, 2:09 PM
Post #2 of 4
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Re: emission test failed
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A P0420 sets when the computer doesn’t see an expected difference between a pre and post converter O2 sensors. In other words something is or has caused the converter to become less efficient or at least the computer thinks this. The cause for this can range from a bad O2 sensor; feeding the computer the wrong information; too an actual condition causing the convert to become less efficient. Things like excessive fuel pressure, defective ECT (engine coolant temperature) sensor, engine misfire, retarded ignition timing, the converter itself and the list could go on but I’ll stop here.
All of these things can be tested for with the proper equipment and the knowledge to operate the equipment. So I’m going to suggest that you take the car in and have it diagnosed; short of that you’ll be throwing parts at the car until you trip over the actual problem.
Dan.
Canadian "EH"
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Guest
Anonymous Poster
Mar 10, 2008, 3:16 PM
Post #3 of 4
(3066 views)
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Re: emission test failed
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thanks for the reply, car runs great, no misses, fuel usage is the same as it always was, the check engine light will go off and stay off for a week or 2, then when my wife fuels up, bingo, in a day the light comes back on.......
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DanD
Veteran
/ Moderator
Mar 11, 2008, 4:41 AM
Post #4 of 4
(3057 views)
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Re: emission test failed
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Your wife filling the tank is likely just a coincidence or by doing so, she has brought the vehicle back to where the computer will run diagnostics.
The computer only runs an efficiency test or any test for that matter, after a number of parameters have been met. As in a predetermined engine temperature, number of minutes the engine has run, the speed the vehicle is at, the level of fuel in the tank and perhaps whether the vehicle is decelerating.
These parameters or criteria are programmed into the computer so that when it runs a test procedure, you should not be able to tell or feel that it’s doing it.
If those criteria have not been met during the next three drive cycles, after the malfunction indicator lamp (MIL) has come on; the light will be turned off, because the portion of the computer that monitors faults hasn’t seen a fault.
A drive cycle is after the vehicle has been started, brought up to temperature, driven a number of minutes, has reached a speed that allows the computer to operate all emission devices, brought back to a stop and the engine turned off.
If the vehicle has met the conditions to run diagnostic tests and a fault is detected, the light will remain on or come back on.
But believe me, if you’ve seen the MIL more then once and the code is the same; there’s a problem. A problem which may not give you any drivability symptoms but whatever the cause might be; it’s likely damaging another emission device.
I’m still going to suggest having the MIL light diagnosed; it would be a shame if you allowed a relatively inexpensive sensor or wire connection repair, burn out hundreds of dollars worth of catalytic converter.
Catalytic converters do not die of natural causes; they are murdered! LOL
Dan.
Canadian "EH"
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