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Engine Light

What could be some of the problems with a engine light that comes on when you turn the car on.

It is supposed to glow for a couple of seconds on start-up as part of the self-test. It should go out after a couple of seconds with the engine running. It will stay on if the engine is not started. This is completely normal.

If the light behaves differently, please include the year and engine option for your truck.

It is a 2003 Jeep Grand Cherokee and the engine light stays on the entire time you are driving places. Do I need to worry about this?

Yes, you do need to worry about this. And the potential causes list is long and varied. Some an be engine-destroying, some are minor.

could be as simple as a loose gas cap or ??? get the codes read for a diagnosis of problem(s)

The Check Engine light is on because the car’s computer has sensed a problem and set a Diagnostic Trouble Code (DTC). Most auto parts stores can read theses codes for free. Get them read, in a format similar to P0301, and post them here. We can help you better understand the problem if we have codes.

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 P1234) 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.

The code is P0456

BB The ECM has detected a large leak in the EVAP BB system during a system monitor test.


BB1 defective, loose or missing fuel cap

BB2 EVAP canister broke, hose cracked or not connected

BB3 purge or vent solenoid defective

BB4 vacuum leak at engine

Very confusing, I guess I should bring into a mechanic to look things over.


Actually most people try replacing the fuel cap. Often that is the problem, it may even be just a loose cap.

That list if more or less a good order to check things out.