Why are you supposed to leave the battery out for a certain amount of time if you unplug it? I had someone do some work on my car and I don't know if he waited. Will that affect anything? I think it has to do with things reseting but I'm not sure.

 

To let the power out of the PCM so it goes into relearn mode when you start it back up. Basically so it takes into account your new mods.

 

Not really. It sounds like you may be refering to the residual charge that is left in your electircal system when you remove the battery. Leaving the battery out would only allow the system to discharge.

 

Umm..no.

Disconnecting the battery from the car for an extended period of time WILL RESET the PCM.

It will also reset the stereo settings that you may have programmed into it.

So, yes, disconnecting the PCM will put the PCM into relearn mode.