Rep Power: 0

I bought a new battery for my 2010 LX. The old battery was out overnight. I installed the new battery, attached the positive cable then the negative cable. As soon as I put the negative terminal on the negative post, the engine started! There was no key in the ignition. I ran and got the key, but since it was in the "off" position, I didn't know what to do. I turned it to the first position then back, but it made no difference. I disconnected the negative terminal, but it still ran. I got back into the car to think of what to do and when I put my foot on the brake (probably a coincidence), the engine stopped. I reattached the negative terminal and this time it didn't immediately start. I started the engine with the key then turned it off. Everything OK.

What happened?

 
Rep Power: 367

likely the same cause your battery was drained. Some short circuit somewhere

 
Rep Power: 0

My wife reminded me that the car has remote start. The remote start remote is separate from the key so it may be aftermarket. I can't find anything about it in the owner's manual. Starting must have been initiated by getting no power for a while then connecting a good battery. Seems dangerous.

 
Rep Power: 222

Relay in the remote start box may have been stuck on

 
Rep Power: 0

Where is the remote start box?

Did Honda offer remote start on the 2010 Civic?

 
Rep Power: 222

Somewhere under the dash, the wiring coming out of it wont look factory