openecu.org

My friend fried his 2005 STI ecu while doing a swap, I opened it up and it looks like one diode is fried. D505, can someone help me identify the part number for it? It says D.4 and 4J on the package. SMD code book lists 4 diodes that start with D4 but none of them are the right package.

Here is the picture of the diode.

Are you sure it's fried? Diodes are one type of components you can often test in-circuit with a multimeter.
It's hard to tell from the photo but it may just have the coating scraped from the top.

It's fried for sure, you can't see it from the top, but the casing is split in the middle. My friend shorted one pin of the ecu and there was enough current to melt the pin, the diode was next in line.

Hmm, yes I should have noticed the brown markings on the PCB where the magic smoke escaped.
It's likely to be a general purpose rectifier diode or schottky , 1A - 2A or so. Measure one of the 'good' ones to see if it's a schottky or not.
Give GF1A will probably do the trick even if it's not exactly the same part. Get a fast recovery one if you think it needs to be. http://www.newark.com/vishay-general-se ... dp/27H4535
For a 1A schottky, try this or similar:
http://au.mouser.com/ProductDetail/Vish ... AgZeKhc%3d
It'll probably be the better option anyway.

This part is looking as reverse power protection diode. Any 10A 40V diode may be used instead of it.

But. Being completely melted this diode could not prevent the ECU from working provided power is applied correctly.
That means that melted diode failed to protect ECU circuitry from reverse voltage applied.