Service Engine Soon Light????????

We are driving a 98 STS, the engine has 70,000 miles. The above "Service Engine Soon " light just came on and stayed on. There will be about 1,000
miles put on the car before it can be checked. The miles will be put on in the next 7 days. The engine runs fine, starts right up, no smoke from engine, and burns about a quart of oil every 4 to 5000 miles. Have not detected any miss fires etc., etc..
My question is; what could possible happen to the engine in the short amount of time it would be driven? About how much $ will it take to find out what is wrong? We just don't want to drive the car if the engine could blow, or something like it. Any advice will really be appreciated.
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