Disconnect the battery and then reconnect it. Or bring it to an auto parts store and they can hook it up to the tester that they have for it, tell you what's wrong with it, and then it will reset.
On a 1998 Mercury Sable : The " Service Engine Soon " light is the same as a " Check Engine " light Something is effecting the engine emission controls It might go out by itself or if it doesn't and you have used the vehicle a few times ( from a cold start ) and have topped up the gas tank since you first noticed the warning light , then you should have the vehicle scanned for any trouble codes to help diagnose and repair the problem ( P.S. I'm not a mechanic / technician )
My auto lamp light sensor is not working on my Mercury Sable 2002. Why?
This car does not have daytime running lights.
I have a 1996 Mercury Sable and it did the same thing. The fix was a new transmission. My mechanic noticed that the car was running higher RPMs than it should have after replacing an engine that blew a rod through the engine because of the bad transmission.
You have the code read with a scan tool to determine which cylinder.
To reset the service engine soon light on a 2006 Mercury Mountaineer, you can buy a scan tool. Make sure you note down the numbers before scanning.
With an OBD2 scanner.
The 1993 Mercury Sable backup light relay switch can be found beneath the drivers side dashboard. The backup light relay switch will be above the accelerator pedal.
The check engine light would illuminate and set a code for the bad O2 sensor.
Fuel filter
If your check engine light is blinking that means an engine cylinder misfire has been detected - have the vehicle scanned for any trouble code(s) to help diagnose and then repair the problem
The engine doesn't need to be running. Just turn on the keyswitch with the code scanner connected.