Part no. labelled is CA 42 or GA 42
I think it is the later.

Text is on left side and no is on right side.

It's a SOT-89 package.

Part is used as a relay driver in car AC Controller. Relay is used for the AC fan and compressor on off.

I am sure it's a NPN with a Diode as there are identical ones in it. I replaced it with a BD139 and a 1N4007.

I need to source the original part. My SMD datasheets shows nothing.

Any one got any idea on the Exact part no ?

 

It could be the BAW78A/B/C/D, here's the datasheet.

It will be hard to be specific based on that info. Here's a guide to the identifying markings for that specific package, at the bottom, that may help.