Four Check Engine light questions - Focus ZTS

Hi folks,
Just a few questions today:
1. If I normally drive at a 7000-foot elevation, can spending a few days at 2000' cause my Check Engine light to come on? If so, what'd be the cause?
2. If I normally drive in a non-polluted area selling ordinary gasoline, can refilling a tank 1-2 times with gas designed to produce low emissions due to being in a large city with pollution problems cause the Check Engine light to activate? The cause?
3. About once a year, my Focus (2001 ZTS-USA model) has its check engine light come on. From reading my manual it seems that once on, the light will remain even after the cause for the light's illumination has been removed--and that it takes three cold start cycles to reset the light to "off". They define a cold start cycle as starting a cold engine, then warming to operating temps in mixed city/highway driving. Rather than take the car into the dealer if the light goes on, I'll wait the full 3 or so cold start cycles to see if the light goes off before taking the car in for a diagnosis--so far, the light's always gone off on its own. For me, this wait can easily mean a week of driving before I meet the 3-cycle reset interval. The question is then--assuming the car drives/acts/sounds normal, is this wait-and-see approach the best?
4. Refer to 3, above. Assume the Check Engine light comes on due to a one-time event which immediately goes away. It would seem to me that I'd be best served by resetting the light to "off" shortly after it goes on, then watching to see if it comes on again, indicating that service may be needed. For speed of service and for peace of mind before waiting for the full 3-cycle reset to occur, I'd like to reset the light myself. Does this seem reasonable? If so, is there a way under the hood or in the passenger compartment with ordinary tools to reset the light to "off"?
Thanks.
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Craig



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Craig wrote:

Why don't you do the obvious thing and read back the stored code(s) that caused the MIL to come on, then either try and fix it yourself or take it to someone who can?
If my check engine light came on, I would sure like to know *why* rather than guess at it. The ECM will tell you why the light is on.
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..and I would do that how?
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Craig wrote:

If you really don't know the answer to that question, I doubt that trying to fix your own car is the right course of action for you.
You need some sort of device with an OBD-II interface that can at least read back trouble codes. Do a google search. I have read elsewhere that Autozone will read back the codes for free, I haven't looked into it personally.
With the advent of computerized powertrain control systems, the entry cost of doing your own auto diagnosis went up somewhat. That's a fact of life. It is still more cost effective to use the proper tools and procedures for diagnosis than to use the shotgunning approach that is diagnosis by parts replacement.
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http://www.fordscorpio.co.uk/obd2a.htm describes the use of OBD-2 scan tool, available from http://www.obd-2.com / It seems to require an RS232 to OBD-2 interface cable ($122).
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Unless it is something like "fuel cap loose" that isn't worth bothering a mechanic about and can easily be fixed by the owner.
Would be nice on any OBD car if there was a small display that said "Code ____". If it was something like "fuel cap loose" or other easily fixable by the owner problem, display that; otherwise display "see mechanic" or some such thing.
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There is on the focus! u uan use the mileage display to show you fault codes, just put it into test mode.
MC
WWW.FFOC.CO.UK
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"Mark C." wrote:

Unfortunately that does not display all the OBD-II codes, just codes related to the instrument panel itself. I thought as you do, but I found it did not work that way.
Try this- disconnect and plug the EGR vacuum hose and drive until the MIL is illuminated. Then put the tripmeter into diag mode and see if there are any codes reported, then get back to the newsgroup with your results. Of course you should make sure there are no codes showing on the tripmeter before you try this.
I did exactly this and there were no codes reported on the tripmeter display even though the MIL was on at the time.
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Looking at the sequence of events, I'd suspect that the air pressure in your fuel system is not being properly regulated. The cheapest thing to try is a new gas cap. If that doesn't fix it, you might want to have a good shop look at the fuel vapour recovery system.
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