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Check engine light question

QueBert

QueBert

Lifer
Got my Taurus smog'ed this morning and it didn't pass, my Check Engine light has been on for months, the code the tech was getting was faulty O2 sensor. I had both of them replaced with OEM Ford sensors by the mechanics at my moms work, so I trust the work they did. Also, since the light has been on I haven't noticed a drop at all in my gas miliage and when I checked the tail pipe I could tell it wasn't running rich.

Not much of a car person myself, I have an idea. If I unhook the battery the check engine light goes off, it will come back on, sometimes after 30 minutes sometimes after a day. If I was to unhook it and go back to get it Smog'ed again would it work? I remember somebody telling me in the past if you do this it also clears the good codes until you drive it for awhile. They never mentioned how long. I'm 99.9% sure the sensors are good, if the computer is bad , which is all I can think of. I'm sure that's EXPENSIVE to fix. I'm looking for an easy/cheap out here. My tags are due in a few weeks, I'm probably going to have to get an extension as it is. But I have to get it fixed too.

for the checklist thing in the sticky:

2000 Taurus 24 valve DOHC 3 liter
78k miles
no modifications.

 
After being reset, the OBD-II system does take some time before it will show the "ready" signal to indicate that the car can be tested, so it's possible that the car could still fail if you simply reset the light. Are you sure that the O2 sensor code is the only code you're getting?

ZV
 
You should have them check it for another code. Even if the O2 sensors are new some are junk from the factory, it has happened to me. My father is a mechanic and he says it doesn't happen often but there are some bum ones from the factory.
 
Zennmervolt brings ups the issue of the emissions monitors, which are tests that the computer runs, some of which are only run under very specific conditions. For tests in your area, the status of these tests will be checked (they hook the testing machine up to your car's diagnostic port). Because certain older cars had computer bugs which caused some monitors to never be set, there is some margin. However, if you reset the computer immediately before, they'll probably tell you to come back later after having driven around a bit. I think these are the "good" codes you mentioned - they get reset based on driving conditions, and not on time. One of these monitors is the o2 sensor (response), and another one is the o2 sensor heater circuit.

Most o2 sensors have heater elements inside them (yours does guaranteed, look for more than 2 wires connected to each sensor), which the computer tests. If these fail it will throw a code, but the heaters aren't necessary for the sensors to work correctly - they just help them warm up much faster. A bum heater element will have a negative effect on emissions (but only) while warming up, which is why they are monitored. If you could figure out exactly what the codes are that would be a big help.
 
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