By bringing it to a trained mechanic so they can check the engine is running properly (which if the light is on it's probably not)
dash dash
There are pages and pages of things that can cause a check engine light. You need to have it checked with a scantool. Then the code can be diagnosed and repaired.
Have vehicle scanned to determine the problem
have vehicle scanned to determine problem
The easiest way is to unhook the battery for a minute.
You either need a scan tool, or unhook the battery for a minute.
If the 1993 Mercury Villager runs rough when the check engine light comes on and the code reader says 34 and 51, there is a problem with an oxygen sensor and the MAP (Manifold Absolute Pressure) sensor. Both parts together will cost around $200.
With an OBD2 scanner.
There are many, many things that can cause the MIL to light up. You will need to have the problem diagnosed by first reading the codes and going from there.
take it to auto zone and ask them to check and then clear the codes or remove the positive battery cable and press the brake pedal for 30 seconds.
IF the computer was really defective, either the car would not run, or there would be a check engine light due to a fault code.
If you have a bad injector, chances are that you will also have a dead cylinder. Auto zone can check that for free if your engine light is on!Good luck!