what does it mean if my "check engine" light comes on, & then goes off on its own a day later?

Question

it has happened twice in the last year--it comes on & by the time I have a chance to take it in, a day or two later, it goes off on its own.

Answer 1

It really depends on the type of car.
It can come on for any number of reason. In one of our cars, it always comes on when the oil is low. In the other, when the gas is down to 2 gallons.
It can also come on if there is a short in a wire somewhere or if there is a real problem.
I would go ahead and take it in to the shop and let them run a check on it , just to make sure there is no problem. Even if the light goes back off, a problem may still show up in diagnostics.

Good Luck!

Answer 2

It could mean a number of things. The best place to start will be pulling the codes from the computer. Most late model vehicles (even some older) retain ALL error codes until cleared with a diagnostic machine.

Many auto parts stores will hook up their diagnostic machine at no charge to you and pull the code(s). Even if the light is not on the code will remain in the system.

Chances are you're getting an intermittent fault signal from a sensor on the vehicle. For example, your O2 sensor sends out a value to the computer with a range of 1,000 - 5,000...from time to time a chunk of carbon gets lodged on the sensor and it output becomes erratic causing your check engine light to temporarily come on. The carbon knocks loose and the readings go back to normal, the error code stays in the system (unless you're battery goes dead).

It's most likely nothing to worry about, getting the codes pulled however is at no cost to you and could identify a small issue that may grow into something bigger over time.

Answer 3

Most of the answers are on point. the only things i add - or clarify is that it is an intermittent failure and it is setting what is called a "soft code". the computer will continue to check for this problem and if a certain number of ignition cycles (trips) pass without sensing it again - it will turn out the light. if you do take it in and they should be able to pull the "history" data out of the computer. sounds like if it only happens twice a year - and then goes out in a couple days that it is not anything serious - but it would be nice to know what is causing it just the same.

Answer 4

If it goes out on it's own that quick, it's probably nothing to worry about. Modern cars have hundreds of sensors on everything from the motor to the radio and if any little insignificant "hiccup" happens, the darn check engine light comes on. You shouldn't worry bout it until it comes on and stays on for a while. Also, you can take your car to any Auto Zone and they can plug their computer into your car and tell you what the light meant. (that's what I would do)

Answer 5

any time the "check engine light" comes on it is because the computer has been sent a signal from one of the sensors on your vehicle...it is sometimes called an intermittent code but should stay logged into the system to have it checked and that would depend on the year make and model of the vehilce too.

Answer 6

This could be 40 different things. Take it in and have the diagnosis run. There are many conditions which could be acceptable and then go out that would cause this. EGR comes to mind, Airflow, O2, Temperature, etc... Find out with a diagnosis and don't waste time and money guessing.

Answer 7

Have you actually taken it in to have them run a diagnostic test on it (about $75)? It would be better to find out that something is wrong now instead of waiting until you break down on the side of the road and have to pay 75 to tow it and then 75 again for them to run the diagnostic and then the cost of what ever is wrong.

Answer 8

Run it to a Pep Boys or Kragen and they can read the code that's still in memory. Most often it's an O2 sensor going bad but it may also be a misfire caused by a bad spark plug or wire.

Answer 9

Go to your local auto parts chain store and pick up -rent an OBD2 reader. You can pull the codes yourself and even reset your chek engine light on your own.

Answer 10

if it keeps coming on and off,then theres a short somewhere.have auto zone check it out for you.if it came on,then it probably stored a code in the computer and a good diagnoses will pick it up.my guess its the 02 sensor,because i would guess its the most sensitive sensor.