I disconnected my negative terminal to clear a CEL but when I was trying to put it back, it started to spark but I was able to put it on quick and that was fine. Why is this?

I also notice that it will only spark when the side edge will touch the terminal. It would spark and feel like its welding if I was to leave it. It left spark marks on the terminal.

There is current going through as soon as the metals touch, hence the spark.

is your cable ok

if your cable is ok check for a bad ground,
always disconnect the positive first and connect the negative first

if your cable is ok check for a bad ground,
always disconnect the positive first and connect the negative first

^that is incorrect. You ALWAYS make and break the connection w the ground

My cable is good almost looks new. How would I get to see for bad grounding? I already bought the Blackbetty grounding kit but hasn't arrive yet but will be installing those right away.

+1 to the first reply.

Think of it this way: As your car sits (engine off) at any given time, it's consuming power from the battery (clock, ecu, alarm system, aftermarket stereo equipment, lights for any door or hood you may have opened, etc.) until the engine is running. This is why your battery will eventually go dead if you don't drive it often enough to keep it recharged. So anyway, just prior to connecting your battery terminal, all those circuits are enabled and ready to permit current flow the instant you complete the circuit. The arc that you see is the total current demand of all those circuits simultaneously powering up. This is normal. Just attach it quickly and don't fiddle around making and breaking the circuit over and over while you "settle" the terminal into place.

Remember, this is low voltage DC circuitry. Thus, there is a LOT of current flow required to make up the required power demands (since P=V*I, and V is fixed at 12v). In a pinch, you could quite literally weld metal with your little car battery; you're just seeing a very small sample of it and hence the light show.

Thanks for the explanation. I was just so worry that something is really wrong with the car now.

its normal like mismosh said its just cause of the accessories suck current as soon as the neg touches any metal.

i think you got it a little mixed up, its like bionic said negative off first to disconnect and connect if your planning to take both terminals off. The rule you might be confusing it with is that when connecting back then the positive goes first.

yeah sorry about that

^ no biggie, after a dozen years of working with cars and such i can still mix up the "simple" lefty loosey, righty tighty rule...

yeah i'm late to the party here....yes this is normal, it's just how electricity works, no need for concern. keep in mind though that this is also why it's recommended to connect jumper cable grounds to the body of the car and not the battery. lead-acid batteries vent hydrogen as they discharge, increasing the possibility of an explosion from a spark. just a safety tip.