hello,

I am trying to repair a ECU for a Subaru STI, one of the diodes got a bit too much current due to a short in the wiring. I can't seem to find a replacement.

The diode in question is D505, the markings on it are D.4 and second line shows 4J

Package dimensions are 4mm by 2mm by 2mm.

I would highly appreciate any help you guys can render in it's identification.

 

We are getting a lot of automotive requests lately. Enough that we are gathering thoughts as to the limits of assistance we can render. Repairs and mods to ECU's is pretty much off-limits, though. The engine's ability to perform to spec's can be quite critical for emission controls.

To be more specific, that diode could be anything. The designator might specify one type of diode in the ECU for one model year, with that same designator being applied to a different device in another model year. The failure might have been most obvious in that diode, but further harm could have been done to the ECU internals.

Have you posted on an automotive forum - or a Subaru forum? Someone might know enough to tell you that you simply can't repair the board.

 

I posted in a couple other forums, no luck so far. I understand that there is a possibility of other damage that I cannot see, I was trying to replace the diode and do some testing, if the ecu does not work after the replacement it will most likely be scrapped and new one purchased.

 

Don't scrap it.

You will probably have to have the original to exchange it for a new or remanufactured unit. If you don't have a core ECU to exchange, you will likely have to pay a good deal extra for a replacement.

Unless you have access to sophisticated test equipment and procedures, you will not be able to tell if the ECU is working within specifications or not. If it is out of specifications, your emissions will likely be higher than allowed, and you may suffer from poor fuel economy, performance, and even engine damage.

I suggest that you will be better off exchanging for a new/remanu unit than attempting repairs yourself.

 

I am willing to take the risk, if I can find the right diode. I would rather not spend $800+ on a new ecu if I can buy a $1 part to fix it. I understand your concern for the environment, but all emission systems have self diagnostics on all the newer cars and will trigger if anything is not in spec.

 

In the USA, you can get remanufactured units for around $350 if you exchange your original core, or they may be able to repair yours and return it.

If you don't have your original ECU, be prepared to spend another $100 or so.

It's likely that the parts in your ECU are "house marked"; that means custom markings that won't cross-reference to any commercially available part numbers.