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Why would a CEL go out on it's own?

My dad’s car is a 2002 Jetta, 70k, Gasoline, Auto, 2.0



A few days ago he was at a light when the car began to run “very rough” and then the CEL came on. The rough idling went away and the car remained drivable so he made an appointment to see our independent mechanic next week.



Tonight he claimed that the CEL had gone out and I told him to have it checked out anyway. He didn’t seem interested. I suggested that the CEL bulb itself simply burned out maybe (it is a Volkswagen).



So

1. Why would a CEL go out on it’s own?

2. What could be the repercussions of him ignoring this?



Thanks

One of the resons is a bad computer which resets itself. If the computr is bad, the CEL and the roughness will repeat itself every so often and maybe get to be a frequent occurence. Thre could be a lot of other causes.

If the computer is working and the bulb isn’t burnt out, the light should come on when the key is turned to the “on” position but with the engine not running.

There’s any number of problems that can trigger the check engine light that can be sporadic and generally when they’re not doing it, the check engine light will go out. If it seems fine, I wouldn’t pay to have someone check it out, but it might be a good idea to have the codes pulled for free at an auto parts store that does that.

Thanks… I’ll have him keep an eye on it. Thanks for your help too pleasedodge.

IF the Check Engine Light (CEL) is off, there won’t be a stored code, for whatever set it off, in the engine computer. So, just a scan for codes won’t help; and, that is all an auto parts store would do.
The mechanic can, or should be able to, do a more comprehensive scan to look at the general health of the sensors and actuators (such as: egr valve, idle air control valve, purge control valve, others). This can reveal sensors and actuators which are marginal.
When the check engine light comes on again, go to an auto parts store and ask for them to do a scan. Don’t wait until the CEL goes out. Then, bring those code here for cussin’ and discussion. Deal?

Sounds good, I think he has his mind made up anyway. He probably won’t worry about it until the symptoms surface again. Thanks.