2000 subaru legacy b4 twin turbo SBF# 5 KEEPS BLOWING

[Damon99]

Hi so my SBF#5 fuse under the hood keeps blowing and car wont start without it, I have no idea what to check for a short can anyone help me out? Thanks

[doublechaz]

If you can get a Factory Service Manual with the wiring diagrams you can, with some study, see all the things that SBF#5 feeds. Then you can look up where those things physically fit within the car. From there you can visually inspect those wires for spots that have rubbed. I only have the FSM for 1995 so I can't really look it up for you.

 

You might be able to replace the SBF#5 with a light bulb and then move around parts of the wiring watching for the light to change brightness.

 

One important factor for narrowing down the search is, if it started soon after some repair, look near there.

 

Example: My 76 Volare started blowing the brake lights fuse. Sometimes it would last a few days, other times just minutes. I got out the book and found that fuse only fed brake lights and backup lights. The brake lights go from the fuse block to the pedal, along the door sill past the fender fuel cap and across the back of the trunk. The backup light wires go across the foot well to the passenger side, through the lower firewall, then over the trans back to the driver's side to the gear selector position switch. Hmm. I just had the car at the exhaust shop a little before the problem started and there is exhaust on both sides of the trans. Got under there and found where the tech had unmounted the wire for clearance while welding and not secured it again after. So it melted against the exhaust. Fixed in a few minutes under the car. Most of the work was reading the book.

 

Beyond that there are things you can do with a multi meter. If it is a really tough problem then you might need a meter that can also measure DC current from putting a sensor around the wire.

[Damon99]

So I unplugged the main relay that's on the passenger side foot panel and the fuse isnt blowing any ideas on where to go from there?

[doublechaz]

I'd have to see the FSM for your model and year.

 

You could try to go around the car with that relay out and see all the systems that are not getting power, but doing that on paper would be a lot easier than doing it on the car.

 

If you have a multi meter you could examine the relay itself for electrical problems.

 

Another idea is if you have run over any road debris lately that could have kicked up and damaged a wire. Or perhaps less likely if you spilled something inside or have leaking glass.

[ehsnils]

Start with looking in this thread: https://legacygt.com/forums/showthread.php/wants-see-my-vacation-pixi-6216.html

[Damon99]

So I've found out what it is on the wiring diaphragm here it is, FB-38 Can anyone help me out from here? Where should I start checking for shorts?

[doublechaz]

The notation in your year manual isn't exactly like mine, but I think the FB-38 is a circuit ID. On the pages following where you found that there will be a block at the top of the diagrams that says 'to power distribution' and it will have some sub blocks with IDs in them like FB-4, FB-38, etc. When you find the later page that shows the FB-38 ID then there will be a line representing a wire coming out of that sub box and going to one or more items in the diagram like 'ABS computer' or 'overhead lamp' or something. Along that wire there will be markings to say what color it is, and the connectors will be listed along it as well. The connectors usually have two designations like B24 and C15 meaning that it is connector 24 on the Bulkhead harness and 15 on the Cabin harness. Once you have the connector IDs there is a page in the manual that shows 3D sketches of the car with the harness in it and the connectors all IDed. Then you can go to the car and find the connector and undo it and see if it still blows. If it does, the fault is closer to the fuse than the connector you undid, and if it does not the fault is after that connector. As you do all that you will come to a point where you have the run between the closest connector and the device where the fault is and then you can inspect along it for the problem without taking apart the entire car.

[Damon99]

Can you tell me if I'm reading this correctly, is shows SBF-5 and is shows it going to MB-30 and when I look at the Ledgen is says MB-30 is the power window circuit breaker, now my power windows nor seat work could that be the location of my short?

[doublechaz]

I think you got it.

 

It might just be me, but I hate taking door cards off. If it were mine, I would take off just the driver's door card and unhook the harness going to the other windows from the main window switch and check for blow. But first I would just carefully examine the whole door harness going into the driver's door from the body. That is the place that gets flexed the most and has a decent likelihood of developing a problem.

[Damon99]

Honestly I'm not even sure if that's the right diaphragm because SBF powers the fuel pump so it should show that on the diaphragm but it doesnt so I'm wondering if I just read the wrong one hahah, I searched alot and I cannot find the excat wiring semantics for a 2000 subaru legacy B4 RSK engine is EJ208 if anyone has a link or anything itd be muchly appreciated