Quote Originally Posted by Otterbatcat View Post
Yes, your main electronic control module.

Remove the ground cable from the battery for several minutes...do not have your key (ignition) in the ON position for this.

Reconnect and start vehicle. If no engine light....drive truck around the block once or twice. If no light, I think you're good.

If the light comes back on, on restart or during your short test drive, the hard fault is set. I'd follow others advice at that point and get the actual code your truck has *somewhere* (auto store, etc) ...and Z has some solid advice about the filler neck if your light/code still exists.
On the newer ones you need to turn the lights on and try to start it with the battery disconnected or wait a really long time to fully drain the system. Otherwise it'll hold the information. Also car may run rough for a minute or gas mileage drop for a short time when it restarts after this as the computer needs to relearn what setting it had before.

OBD scanners are so cheap now that it's almost pointless to not have one though, and then you can reset it yourself w/o all the hassle.