Yes, some folks have said it has to be cycled 50 times before it goes away, I'm not sure that's true but if the CEL came on because the cap wasn't on, run it for several times and it should disappear....don't know about 50 times but that's what I've heard.
The OBD (on board diagnostic) system checks all the emissions systems for faults and throws CEL and stores a DTC (diagnostic trouble code) for any that it finds. If the ECU sees the fault gone for a number of start up/warm up cycles (more like a dozen, not 50) it will turn off CEL. Since the fault is gone (like a loose gas cap, or maybe a hose comin loose that you tighten back on) no need to have a CEL. It does keep the DTC in memory so the technician who reads the codes at the next service will have a record of intermittant faults that have occured since the last service. IF the ECU sees a fault that can cause further damage (say a plug wire is off and one cylinder is misfiring, dumping raw gas into the cat converter) then it gives a flashing ECL which means get service ASAP! Hope this helps. http://****************.com/smile/emthup.gif
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