Onboard computer

[emanuelme]

So I know there is an onboard computer that will relay information as what is causing a check engine light to come on (or anything of the sort). I am wondering is this onboard computer stores that information after a repair or does it only display what is currently wrong. In other words, suppose the car is leaking engine coolant and the onboard computer notices this. It displays the check engine light. I bring it to the mechanic who fixes it. The check engine light is no longer on... but, is the information still stored, namely that the check engine light came on at 'x' time because of a coolant leak...

Thanks.

[E36 Phantom]

AFAIK it stores codes until it is reset/battery is unhooked. However, I'm sure all mechanics will reset it after they fix the car. Also, there are 2 Check engine Lights. One of them is connected to the "Check Control" which the MID/OBC displays when you press "CHECK". This will display a message on the MID/OBC and illuminate a light that simply displays "CHECK". The other one is the "real" Check Engine Light, which monitors anything that will affect emissions. This will store the codes in the ECU, and is the one you use the pedal trick to get codes from. Something like leaking coolant will not set off either light, low coolant will illuminate check control.