Engine yellow check light on

Since 1996, all cars in the US are required to support something called On Board Diagnostics, version 2, better known as OBD-II. This is a standard calling for a common connector on all cars with a communication protocol to allow information to be read regarding important systems in the car. The OBD-II connector is required to be located in the driver's compartment where you can plug in a code reader to download the Diagnostic Trouble Codes, or DTCs that tell you what the error is.

Without the code reader, the only way most cars have to notify you that there's a problem is to turn on that yellow "check engine" light, which is more properly termed the MIL, or Malfunction Indicator Light in OBD-II parlance. All you can tell from the light being on is that the engine or transmission computer has detected a problem; there is nothing to tell you how serious the problem is, which could range anywhere from a loose gas cap to imminent and catastrophic engine failure.

So yes, Harry is exactly right that your next step is to find out what the computer is trying to tell you by getting your codes scanned. Here in the US, most auto parts stores will hook up their scanner to your car for free and give you a readout of the trouble code(s) they find. Given that, you can then look them up online and figure out what the most likely fix is. There are also small bluetooth adapters that you can plug into the OBD-II port and read with a free app on your phone; those can be had online for sometimes as low as $5 USD. Of course, there are also consumer and professional grade dedicated readers that can be purchased anywhere from about $25 to several thousand.

Anyway, however you do it, you'll need to find out what DTCs are being indicated for your car. Once you have them, come on back and add that information to your question and we can help you figure out what you'll need to do to fix it.