Check engine light

What would cause that light to come on?

The engine management computer has detected a problem, and set a diagnostic trouble code. A code reader can read the code, and the code will lead a technician to the problem. Typically the codes are in the format of P0300. Some auto parts stores, like Auto Zone and O’Reilly’s will read the code for free. If you can get the code, post it here for some suggestions. There are some really knowledgeable poeple that can offer some great suggestions.

One of a hundred’s of reasons is a loose fuel cap. Make sure its tight and see if it goes out after driving the car 4-5 engine on-offs with some mileage between.

As has been suggested, the possibilities are really numerous. Have the OBD II system scanned for stored trouble codes, come back here to post those codes, and then the cause(s) can be identified.

The light is an early warning system. The engine management computer has detected something outside normal parameters and is alerting you. Have the computer codes read at an auto parts store or by a mechanic for an indication of the problem area.

Is it a solid light or a flashing light? A solid light usually indicates a minor problem while a flashing light indicates a serious problem. Either way, make sure you get the codes read and get it fixed.

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Regarding warning lights:

  1. if the coolant temp light comes on, shut off the engine ASAP

  2. if the oil warning light comes on, shut off the engine ASAP

  3. if a FLASHING MIL/CEL comes on, shut off the engine ASAP

    ASAP means driving to the berm of the highway right now and not waiting for the next exit.

But if the MIL/CEL is not flashing, then it’s not an urgent indicator.

My car is a 2003 Toyota Corolla. The check engine light came on the other day, and
it stays on while I’m driving. The dealer checked it and told me the “gasket” needs to be replaced. And I got the code: P0171
They said it means the fuel system has air… should I trust them?

DTC P0171 = “System too lean (bank 1)”. The fuel to air ratio is too lean on one side of the engine. This is likely a leaking gasket under the intake manifold…could be some other place.

Thank you! That’s exactly what the dealer told me (no “likely” though). The gasket hasn’t arrived. Is it dangerous to continue to drive? I drive it to work (15 to 20 miles one way). Should I keep the (gas) tank low? Thanks!

You probably drove it for several days with the check engine light ON didn’t you? Driving it a few more days shouldn’t hurt it.
If the engine isn’t misfiring, the fuel/air leaning isn’t severe and shouldn’t hurt the catalytic converter. {Did you notice the use of the word “shouldn’t”?)
The fuel tank isn’t involved with the trouble code P0171; so, put as much fuel into the fuel tank as your wallet will allow.