Something leaking in car

What makes you say something is leaking? Puddles or visible fluids? If so please describe. Where, color of fluid. None of those codes have anything to do with a leak. Misfires on cylinders can be caused by a multitude of things, and especially the P0300. Do you have the 1.8L?

The P0135 is not necessarily a bad o2 sensor. It's a heated sensor and the code is almost self-explanatory, the heating circuit to it. The P0420 MAYBE is a bad cat, but cats are damaged by lean running, and a vacuum leak, working backwards vacuum leak= lean= ruined cat after a period of time

yes i have 1.8L and i can see few drops on the ground and under the hood its look like something is leaking one of my friend said its because of Head gasket can it really be the issue?

Possibly. But let's not jump too far ahead What gasket did you replace?

i had replaced head gasket and spark plugs 3 months back and color of liquid is not sure but it looks like yellowish but leak is not much little i had into minor accident 2 days back was hitted on front right slightly no outer damage

ok, more questions. Is it-was it-- overheating, before and/or after head gasket job? How does the motor oil look? Have you done a compression check?

And ignore the bank 1 stuff. It only has one bank

no over heating car is driving smooth no such issues while driving, heating and AC also works good only when i put fan on or ac it gives some scratching noise some time other than that car is working well it consumes more oil usually i have to do oil change in 2000-2500 miles and other thing i'm worried is there is something leaking

Hopefully when the head was off it was sent out for a magnaflux at least, to check for cracks in head, and maybe even milled just SLIGHTLY, and a valve job. Sure, it cost more but is money well spent. Since the car is running well, and not overheating, if the fluid leak is small I really wouldn't worry about it. But if your motor oil begins to look like chocolate milk, or if you see bubbles in radiator while running (don't pop a hot cap), do a compression check. If none of those things happen, I wouldn't be too concerned. Look around for obvious vacuum leaks, like a hose off. If you find one, that is probably the main problem

ok thanks for reply

I forgot, if it is blowing white/blue tint smoke from tail pipe, DO the compression check