Just installed HKS downpipe and my CEL came on. Does anyone know how to shut that thing off?

 

reset it, unplug the battery negative one for like at least 30 sec, then plug it back...

correct me if i was wrong , at least I've done that all the time

 

You are probably throwing a p420 code since you are running a catless DP.
There are a few ways to remedy the CEL.
1. MIL eliminator fix ( you splice a resistor into your rear O2 sensor)
2. Buy a scan tool at kragens (about 200 bux) and clear it yourself.
3. Leave it alone because it will eventually go away. Eventually it will figure out that the car is running fatter and pull back fuel. Then the ECU will take away that CEL. But ,depending on your driving (freeway or streets), the ecu will correct the leaness. Thus sending yet another CEL. It's a vicious circle with CELs and p420.
Chris

 

So how long do estimate I have to wait for the ECU to clear it on it's own before I go out and get it fixed?