Sometimes ECU won't reset
 

My SES light comes on all the time and my car drives like crap when it's on - looking into some possible fixes, but aside from that, I've notice sometimes it's impossible to reset the ECU.

I'm pretty good at it now - I can do it without a stopwatch and have it all memorized. But you can't reset the ECU after the car has been running. It seems to have to sit for some specified time - anyone know the amount of time it must wait?

You can tell too when it's not going to reset, because normally when you turn the ignition to ON, it'll do 4 beeps as it goes thru all the settings on the computer display gauge. When it does those beeps, it's possible to reset the ECU. When it doesn't, you can't.

So an example would be I go to start my car after work. I get it started and wait about 30 sec for it to get the oil circulated while I continue to get ready to go. Then the SES light comes on. I say screw that, I don't want to drive my car with the light on because I know it's going to drive like crap (a whole other subject)

So I turn off the car to reset the ECU, and it won't work because the car has already been on.

I can always avoid this by resetting the ECU every single time I get in the car before I start it, but that's a bit of a hassle I think.

Does anyone know WHY it does that - not resetting? And How you can get the ECU to reset after you've already had the car on for a bit?

Man, that sounds like it's malfuntioning.

Have you tried disconnecting the battery over night? If THAT doesn't work then I think something's wrong.

well disconnecting the battery will for sure work, but that's the lame way of doing it

I can reset the ECU, but the car has to sit off for a bit


this is pretty easy to try for yourself - next time you're done driving, turn the ignition to ON and see if you hear the 4 beeps. Compare that to when you get in the car and turn the ignition to ON when it's been sitting for awhile

Are you sure the beeps aren't the seat belt beeps? sorry if that's a stupid question

no they're 4 long beeps, not the repeating 4 quick beeps.

A theory is i wasn't using the master key at the time, but i don't think that's it