yellow check engine light

Yesterday my husbands was driving our car to and from work about 20 miles into the trip the yellow check engine light came on whatcould that possibly mean. Its a 1994 civic dx just turned to 130,000 running good
also.
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So far all we know is that the engine computer (ECU) has decided it isn't getting what it wants to see from something that will affect the engine's emissions. The next step depends on what codes the ECU has stored. In your 1994 you can find that out yourself. Instructions are in http://www.iequus.com/assets/manuals/3173_ICCR_E_14JAN03.pdf with the procedure for your '94 Civic starting on page 18 of the PDF. Where the instructions say to insert a "Code Reader" it means to connect the two terminals in the plug with a wire. (I bought the book with the "Code Readers" for all the cars listed - Toyota and Honda are little jumper tools while the Nissan is a plastic screwdriver - for $35. D'oh!) Instructions for interpreting the codes follows on pages through 25... you will probably want to print them out so you can take them to the car. The same pages also have instructions for clearing the codes, which will turn off the yellow light if condition was transient or after fixing the cause.
I know it would be easier to just reset the codes and see if it is okay, but it really is important to know why it is disturbing you. Whatever it is, as long as the car drives the same it won't hurt it to drive in town or gently on the freeway. There is (at this point) a risk that the mixture could be very rich, which could damage your catalytic converter through overheating if pushed hard for more than a moment. Once you determine fuel consumption is fairly normal that restriction is lifted. The light is there to warn the driver of emission related failures that would otherwise not be noticed, although in later years even transmission codes have been piggybacked onto it. In fact, on 1996 and later systems even a loose gas cap will light the light, and on those models a special electronic tool is needed to read the codes and reset them. That's progress?
Mike
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It means a sensor has either failed or returned an invalid signal to the ECU.
You need to get the code read, like Mike Pardee says. A paper clip can be your "wire" for jumping the terminals of the Service Check connector.
The usual procedure here is to make note of the code, then clear it from the ECU according to the steps in the iequus document. If the Check Engine light comes on again later, see if the code is the same. If it is, report back here and somebody can point you in the right direction.
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TeGGeR

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go the car checked and fixed it was the heated o2 sensor. thanks guys for being right.even though i was sticker shocked
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