bugblatterbeast Posted August 4, 2006 Share Posted August 4, 2006 Ok, I found the page in the vacation pix that provides some more info; look at 08 - Engine / Cooling System / 02 - Radiator Fan System page 1. You can see how the ECM hooks into the coil of the Main Fan Relay 1 (at pin B7 on the Main Fan Relay 1) - I bet that's where the diode was replaced with a resistor. I'll keep poking to find more info. -Ryan I'm guessing the old relay had a reverse connected diode in parallel with the coil. This is fine if the low side driver in the ECU is BJT based (with a properly designed snubber) but Subaru probably used a n-channel fet in the ECU or put a zener clamp on that line to ground. You end up with the parasitic body diode of the fet (and/or the zener clamp) and the clamp diode in the relay forming a pretty low impedance path for negative going transients between V+ and ground. They probably fixed the issue by tossing some resistance in series with the relay's clamp diode. Link to comment Share on other sites More sharing options...
bosco Posted August 4, 2006 Share Posted August 4, 2006 I'm guessing the old relay had a reverse connected diode in parallel with the coil. This is fine if the low side driver in the ECU is BJT based (with a properly designed snubber) but Subaru probably used a n-channel fet in the ECU or put a zener clamp on that line to ground. You end up with the parasitic body diode of the fet (and/or the zener clamp) and the clamp diode in the relay forming a pretty low impedance path for negative going transients between V+ and ground. They probably fixed the issue by tossing some resistance in series with the relay's clamp diode. wow, what he said. lol bosco Stay Stock Stay Happy Link to comment Share on other sites More sharing options...
bugblatterbeast Posted August 4, 2006 Share Posted August 4, 2006 wow, what he said. lol bosco working in a large electronics company, I get to see this sort of thing happen often enough . I'm guessing the history of their design screw up isn't too far from the following: engineer A designs the ecu fan relay driver. He assumes he is going to be dealing with the inductive kick from the relay and adds a clamp diode to that line. He then specifies the maximum allowable kick for the group of engineers working on the bits outside of the ecu. engineer B working on the external bits needs a big ass relay to drive the fan (notice it is the big relay that is being swapped). By the time the relay is big enough, he notices that he has exceeded the maximum kick specified by engineer A. To make the design more reliable, he specifies a relay with an internal clamp to contain the inductive kick at the relay. oops.... engineer B wasn't aware of the internal clamp structure of the ECU and engineer A wasn't expecting a self clamped relay. now management has a deadline to meet so the system is rushed to production before the fault is found Link to comment Share on other sites More sharing options...
bosco Posted August 4, 2006 Share Posted August 4, 2006 bugb, i'm glad there's people like you to help people like me. question i read the text on this does this affect all lgts or a certain vin number batch. bosco Stay Stock Stay Happy Link to comment Share on other sites More sharing options...
TravisS Posted August 4, 2006 Share Posted August 4, 2006 bugb, i'm glad there's people like you to help people like me. question i read the text on this does this affect all lgts or a certain vin number batch. bosco Check the TSB, they fixed the problem somtime on the '06 models and there are VINs listed Link to comment Share on other sites More sharing options...
rc0032 Posted August 4, 2006 Share Posted August 4, 2006 Check the TSB, they fixed the problem somtime on the '06 models and there are VINs listed Link? Link to comment Share on other sites More sharing options...
TravisS Posted August 4, 2006 Share Posted August 4, 2006 Link? http://legacygt.com/forums/702796-post18.html But I'll go ahead any copy paste it for ya The modified relay was used in production May, 2006 starting with the following VINs: Legacy Sedan: 6*220026 Legacy Wagon: 6*361122 Outback: 6*361121 Link to comment Share on other sites More sharing options...
rc0032 Posted August 4, 2006 Share Posted August 4, 2006 Ok more slow me time – If I replace the relay problem solved or is there still the need to reflash the ECU like previous threads have stated? Link to comment Share on other sites More sharing options...
TravisS Posted August 4, 2006 Share Posted August 4, 2006 If I understand the TSB correctly, the fix requires a new ECU, not a reflash. The ECU is phyically damaged by the bad relay, thus just replacing the relay is not enough. Both or nothing. Link to comment Share on other sites More sharing options...
SuperhawkLGT Posted August 4, 2006 Share Posted August 4, 2006 I'm guessing the old relay had a blah blah blah. This is fine if the blah blah in the ECU is Blah blah (with a properly designed blah) but Subaru probably used a blah blah in the ECU or put a blah blah on that line to ground. You end up with the yada yada yada (and/or the blah blah) and the blah blah in the relay forming a pretty low yada yada yada. They probably fixed the issue by tossing some yada yada yada blah blah. Translated that for ya. Link to comment Share on other sites More sharing options...
RyanE Posted August 4, 2006 Share Posted August 4, 2006 I'm guessing the old relay had a reverse connected diode in parallel with the coil. This is fine if the low side driver in the ECU is BJT based (with a properly designed snubber) but Subaru probably used a n-channel fet in the ECU or put a zener clamp on that line to ground. You end up with the parasitic body diode of the fet (and/or the zener clamp) and the clamp diode in the relay forming a pretty low impedance path for negative going transients between V+ and ground. They probably fixed the issue by tossing some resistance in series with the relay's clamp diode. I'll have to remember that - I'm building a DIY RPM triggered circuit that drives a relay, and only have it set up with a diode across the coil. I have a 16 volt zener set up to protect the circuit, but should probably add a resistor as well. For $15 for the updated relay, perhaps I can convince my dealer to just give me one. Who knows, they may just do it... -Ryan Link to comment Share on other sites More sharing options...
rao Posted August 4, 2006 Share Posted August 4, 2006 Ok more slow me time – If I replace the relay problem solved or is there still the need to reflash the ECU like previous threads have stated? Your ECU definately needs to be replaced. Sounds to me like once the relay goes bad it takes that portion of the ECU with it, the circuit must alwaysw go to ground once the relay fails. Luckliy for everyone it only seems to effect only that specific small portion of the ECU, otherwise cars would have been dying all over the place. I don't know a lot about electronics, but I always thaought that diode relays were "better" then resistor relays. Can someone point me to an explanation of the difference. Rob IF YOU CARE ABOUT YOUR CAR YOU SHOULD NEVER DRIVE IT Link to comment Share on other sites More sharing options...
Vimy101 Posted August 4, 2006 Share Posted August 4, 2006 Thanks for the heads up. Looks like my Spec. has the suspect part. I'm about to do a fairly cold start so I'll check to see if the fan starts up right away if that is indeed symptomatic of the problem. I don't know if it would be related but there was a poster a few days ago complaining of a hum coming from the engine after shut down. He wasn't very car savy so he couldn't really track down the source of the sound. Link to comment Share on other sites More sharing options...
JBLU24 Posted August 4, 2006 Share Posted August 4, 2006 any idea if those of us that are stage 2 will get a new ecu or will they say that the cobb ap caused the relay failures ??? Link to comment Share on other sites More sharing options...
rc0032 Posted August 4, 2006 Share Posted August 4, 2006 Thanks for the heads up. Looks like my Spec. has the suspect part. I'm about to do a fairly cold start so I'll check to see if the fan starts up right away if that is indeed symptomatic of the problem. I don't know if it would be related but there was a poster a few days ago complaining of a hum coming from the engine after shut down. He wasn't very car savy so he couldn't really track down the source of the sound. Its actually worse than that…You don’t even need to turn the car on to hear the fan, just turn it to accessory mode (windows can go up) and the fan will kick on. Link to comment Share on other sites More sharing options...
Jon in CT Posted August 4, 2006 Author Share Posted August 4, 2006 If I replace the relay problem solved or is there still the need to reflash the ECU like previous threads have stated? There was never an ECU reflash for the fan problem. If your fans are working OK now, simply replace the relay with the new part. If your fans are on all the time, take it to the dealer who'll replace both the relay and the ECU. Link to comment Share on other sites More sharing options...
thepdmm Posted August 4, 2006 Share Posted August 4, 2006 So when you guys are having this fan sticking on problem does it literally stay on all the time as long as the key is at the on position (no matter the temp outside/engine or if the engine is on or off).. My electric fan (driver's side fan) came on sometime between the time that I started driving home and the time I got home. I pulled in the driveway and heard it running so I drove around the block (kept the car moving) and came back and it was still running.. shut the car down and started it right back up and it didn't kick on? is this a problem or is it just warm out? Link to comment Share on other sites More sharing options...
rc0032 Posted August 4, 2006 Share Posted August 4, 2006 ^early stages Link to comment Share on other sites More sharing options...
TravisS Posted August 4, 2006 Share Posted August 4, 2006 So when you guys are having this fan sticking on problem does it literally stay on all the time as long as the key is at the on position (no matter the temp outside/engine or if the engine is on or off).. Correct. I go outside in the morning, it's about 55 out, I turn the key and I get fans blasting away. Link to comment Share on other sites More sharing options...
Abandonhope16 Posted August 5, 2006 Share Posted August 5, 2006 Is it VINs with the last 6 #s coming after 660026 or before? I'm not sure if I have the problem. When I turn on the car the driver side fan turns on, but only when I turn on the A/C will the other fan kick on. Thanks. Link to comment Share on other sites More sharing options...
ilh Posted August 5, 2006 Share Posted August 5, 2006 I've never had the fan problem, but I'm wondering if I should just buy the $15 relay myself and install it to avoid ECU problems down the road. I doubt SOA would do this without a demonstrated problem (even though it could save them in the long run). Link to comment Share on other sites More sharing options...
Opie Posted August 5, 2006 Share Posted August 5, 2006 Is it VINs with the last 6 #s coming after 660026 or before? I'm not sure if I have the problem. When I turn on the car the driver side fan turns on, but only when I turn on the A/C will the other fan kick on. Thanks. The TSB applies to the VIN's before the numbers listed.... Link to comment Share on other sites More sharing options...
mccorry Posted August 5, 2006 Share Posted August 5, 2006 I've never had the fan problem, but I'm wondering if I should just buy the $15 relay myself and install it to avoid ECU problems down the road. I doubt SOA would do this without a demonstrated problem (even though it could save them in the long run). I'm thinking the same thing..... Link to comment Share on other sites More sharing options...
SuperhawkLGT Posted August 5, 2006 Share Posted August 5, 2006 any idea if those of us that are stage 2 will get a new ecu or will they say that the cobb ap caused the relay failures ??? AP will void your warranty for any ECU related problems unless you have a really cool dealer. Unmarry FTW. Link to comment Share on other sites More sharing options...
Jon in CT Posted August 5, 2006 Author Share Posted August 5, 2006 Unmarry FTW.Duh! They're going to replace your ECU! Link to comment Share on other sites More sharing options...
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