Sangerboy Posted July 1, 2009 Share Posted July 1, 2009 Hi , new to this forum, I'm an original owner of a '95 Legacy Outback (260K miles). It quit running yesterday, I'm suspicious of the ECU (tach and speedometer just dropped to 0, no power to the OBD II port) engine turns over and other gauges work but no fire. Coil checks out OK. Before I buy a new ECU (expensive I know) I have a nagging feeling about a fuse or relay. Is there a fuse or relay that sends power to the ECU? In the main fuse/relay box what do SBF 1,2,3,4,5 and 6 control? thanks for any help. Greg Quote Link to comment Share on other sites More sharing options...
OB99W Posted July 1, 2009 Share Posted July 1, 2009 Welcome to the forum. Fuse SBF-2 would be a good place to start checking, since it provides power to the ECU, fuel pump relay, main relay and the OBD-II connector. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted July 1, 2009 Share Posted July 1, 2009 ECU is not an item you would replace with a new unit anyway. They fail so rarely that it just doesn't make any sense. I'd be very surprised if your ECU failed (for no reason), but if it did just buy a used one for $50 or less. Quote Link to comment Share on other sites More sharing options...
Cougar Posted July 1, 2009 Share Posted July 1, 2009 Welcome, and hope you like it here. I agree with the above advice. Fuse SBF-2 is what you need to check and ECU's are one of the last things on the list to replace since they are very reliable but can and do go bad on occasion. Your nagging feeling of checking fuses is a good one along with suspecting relay problems. Looking for bad fuses is the first thing to do when a problem like this happens in my opinion. By proper testing before replacing parts you can avoid needless parts replacement and wasted time an money. Quote Link to comment Share on other sites More sharing options...
Sangerboy Posted July 2, 2009 Author Share Posted July 2, 2009 Thanks for the welcome and the help, you guys nailed it. SBF-2 looked good on an initial check but after a more thorough eval it proved to be the culprit. All is well, thanks again. Next stop 300K miles:) Quote Link to comment Share on other sites More sharing options...
Cougar Posted July 2, 2009 Share Posted July 2, 2009 You're welcome for the help and thank you for the feedback. A lot of folks get fooled by the fuses thinking they look ok at first glance. Quote Link to comment Share on other sites More sharing options...
OB99W Posted July 2, 2009 Share Posted July 2, 2009 Thanks for the welcome and the help, you guys nailed it. SBF-2 looked good on an initial check but after a more thorough eval it proved to be the culprit. All is well, thanks again. Next stop 300K miles:) You're welcome, thanks for getting back to us, and congrats on resolving the problem. Quote Link to comment Share on other sites More sharing options...
Sangerboy Posted July 3, 2009 Author Share Posted July 3, 2009 Well of course I spoke too soon, When SBF-2 is replaced and the battery hooked up everything is fine and power is present at the OBD II port. As soon as the key is turned to run position it blows the fuse link. After studying the wiring diagram it appears that the only thing activated on this circuit in run mode is the fuel pump. I disconnected the fuel pump harness and tested, still pops the fuse, I removed the fuel pump relay and tested, it still popped the fuse. Is there anything else on this circuit (SBF-2) that is activated when the ignition switch is turned to on? I'm going to check all the other fuses just to see if anything else is amiss. If I figure anything out I'll report also. Thanks again Greg Quote Link to comment Share on other sites More sharing options...
Cougar Posted July 3, 2009 Share Posted July 3, 2009 (edited) I was wondering about that. Fuses rarely blow for no reason. I think I may know where the trouble is. The fuse SBF-2 ties to the Main Relay along with the fuel pump relay and like you said, some other points also. The Main Relay turns on with the ignition switch as does the fuel pump relay. The main relay then connects power to the ECU a.....nd the O2 sensors. My bet is the wiring to one of the sensors is up against the exhaust and shorting to ground. If you pull the Main Relay and the short clears I think you will find that is the case. Edited July 3, 2009 by Cougar Quote Link to comment Share on other sites More sharing options...
OB99W Posted July 3, 2009 Share Posted July 3, 2009 Besides the things that Cougar mentioned, the main relay powers a few other circuits. If you don't find a short at one of the O2 sensors (could be due to melted wire insulation or internal short), other connections are: - MAF, yellow wire - Fuel injectors, yellow/blue wires - The sneaky one -- under the dash, often hanging down where it can get stepped on and short to something, is the diagnostic connector for the Subaru Select Monitor. It's a 9-pin yellow one, and the yellow/red wire going to pin 5 is the supply lead. Quote Link to comment Share on other sites More sharing options...
Sangerboy Posted July 5, 2009 Author Share Posted July 5, 2009 OK here's the follow up, Cougar and OB99W, you guys rule!! Cougar you set me on the right path, I disconnected the main relay and tested with success- no blown fuse. I then disconnected all components that run through the main relay and reconnected the main relay then tested- success again no blown fuse. I then reconnected each component and tested after each connection until I found the one causing the short. Sure enough it was the pre-catalyst oxygen sensor. No fried or grounded wires, the sensor had just gone bad. Replaced it and the car is running great again, going to take it in to get it smogged and registered for another couple of years. Thanks again for the help, it is well appreciated Quote Link to comment Share on other sites More sharing options...
OB99W Posted July 5, 2009 Share Posted July 5, 2009 That sounds like you nailed it. Congrats, again. Quote Link to comment Share on other sites More sharing options...
Log1call Posted July 5, 2009 Share Posted July 5, 2009 Yeah, nice work guys! Quote Link to comment Share on other sites More sharing options...
Cougar Posted July 5, 2009 Share Posted July 5, 2009 Good work on tracking down the trouble and glad we could assist you in the hunt for the trouble. Thanks for the feedback on it. Quote Link to comment Share on other sites More sharing options...
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