pgmfi.org

Hi

Somehow I blew up a large diode in my ECU. Does anyone know what this diode does or why it would have fried? I have an 89 Prelude 2.0 SI 4WS with a PK2 ECU. The diode is labeled D13 on the board.



Here is the full story of what happened:

Started the car in the morning and noticed the charging light flickering a little bit. Decided to check it out later and kept driving. About half way to work the engine died. The main battery (70 amp) fuse blew. Disconnected alternator and tried to start, but whenever I do that the #38 fuse (PGM-FI Main Relay) in the engine bay relay box blows. Looked at the main relay and all the wires going to it are melted, but the relay itself tests good. Traced a short on the yellow/black wire back to the ECU, where I found the charred diode. I'd like to figure out exactly what happened before I fry another ECU.

I found a few threads on Honda-Tech which I think are the same or a similar issue, but none of them were ever resolved.
https://honda-tech.com/forums/honda-crx ... s-2583069/
https://honda-tech.com/forums/acura-int ... t-2865160/
https://honda-tech.com/forums/engine-ma ... e-3084048/

That is TVS SR4418

viewtopic.php?f=2&t=16828



Replacement can use https://www.semicon.sanken-ele.co.jp/sk ... _ds_en.pdf

It's there in case the battery terminals are reversed so it draws enough power to pop the fuse and not damage the internals of the ECU. (reverse battery protection)

either your battery terminals are reversed (or ECU pins) or your alternator is not producing clean enough DC power. (ie rectifier is blown and it's now producing AC voltage as well)

Thanks guys. You were right on. It was the alternator. It's unfortunate that when it crapped out it took so many other things down with it.

I replaced the whole ECU, but I'm also going to try and repair the old one. The PZ628 diodes are kind of hard to find but I was able to get some on AliExpress.