identifying pcb component

Hi, I'm Paul, I'm new to this forum, I was directed here by someone at an electronics store who had no idea what this component is, could someone here please identify this component? I've tried googling it but to no avail! The board itself is for converting analog 12v to w-bus protocol signals (similar to CAN-bus and OBD2) for a webasto heater for a car. I'm not a wizard with electronics (it was pre-made) especially when it comes to CAN-bus and protocols! Any ideas as to what it is and where I can get a replacement would be gratefully received!! Thanks for your time. Paul.

It is a reverse polarity protection diode. It's purpose is to protect your device in the case of somebody connecting the battery backwards. Is it shorted? Does the device blow a fuse as soon as you put it in or apply power to the unit? You can replace it with a non surface mount device if you like. 1n4001 or equivalent.

i am an idiot wrote: It is a reverse polarity protection diode. It's purpose is to protect your device in the case of somebody connecting the battery backwards. Is it shorted? Does the device blow a fuse as soon as you put it in or apply power to the unit? You can replace it with a non surface mount device if you like. 1n4001 or equivalent.

Hi, thank you very much for that, no one I spoke to had any idea what it was. Well, it makes sense, hopefully works too, because, to my embarrassment, I actually connected the wires wrong, in the dark and in a rush... Hopefully lesson learned! Does it matter which way the replacement is fitted? Thanks very much once again! Paul

Yes very much so! Hence reverse polarity protection. The diode acts as a fuse and blows to save the board. Looking at the board, band side of diode to left.

Thanks for that howie, probably another disaster averted!