my driver side headlight will work fine as soon as I turn it on for about 20 seconds, then it will start to flicker and then it will eventually just turn off.
does this mean i need to replace the bulb or is there something wrong with my headlight?

 

May be your igniter box... if it's the bulb it wouldn't turn on at all ?

 

how can i target the problem?

 

is it an aftermarket kit or is it the oem one ??

 

pretty sure its the stock kit but I think it has upgraded bulbs (8600k)

 

switch bulbs. if the good bulb does it, you need a new ballast.

 

how would i replace that and how much is it?

 

get an ebay kit

 

^ what he said...get a ballast/bulb kit for around $120...OEM is pretty steep...i think around $300 for the ballast alone? not sure...

 

It sounds like a bad bulb. My friend with HIDs in his WRX had the same thing happen, the bulb would flicker and shut off. Like someone said, swap the working bulb into the place where the flickering one is and you'll know for sure if it's the bulb.