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Discussion Starter · #1 · (Edited)
2005 OB Limited 2.5. Getting a P0692 error code. Traced it to sub fan relay. The relay will not energize (no control signal coming from ECU to pull it to ground), hence no radiator fan. The other fan works fine. Both fans actually work, sub fan relay works, car wiring is good and no blown fuses. So I traced the issue to the ECU and I'm fairly certain it's a bad transistor on the board not pulling sub fan relay coil to ground. I've identified which component it should be, but the only marking on the chip is GA4Z. There's no company logo. My bet is if I replace this chip which probably costs around $0.25 the radiator fan will work and clear the P0692 code. Any suggestions?? Any schematics or bill or materials for the ECU out there somewhere? I can't find anything on that or this chip which is probably a mosfet....Thanks.
 

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Any schematics or bill or materials for the ECU out there somewhere?
I'm not aware of any schematics or related informaton, on the ECU.

There was a case here not too long ago where a similar component (related to the interior ceiling light control) in the Body Integrated Unit had failed, and the poster was able to identify and replace it: SOLVED: Rear Dome Light Stays On When Set To...

In your case, it's possible Subaru used the same fan switch in the ECUs for a range of models. A used ECU from a recycling yard might be inexpensive enough to warrant buying and swapping the component. (That way, it need not be from the exact same car and there's no need to reprogram a replacement ECU.)

That's an unusual failure. Hope you will keep us informed.
 

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Discussion Starter · #3 ·
I bought an ECU off Ebay with identical part # to mine and dropped it in the car and it works fine. I don't have electronic keys on this '05 limited so no programming needed I guess?..?? I was going to swap the transistor and use my original ECU, but actually don't need to . That's great because the board is conformal coated which is a pain to scrape off and solder to. $40 and all good. I think the ECU's only need to be reprogrammed if you have electronic keys, but I'm not 100% on that. I know this one with the same model # dropped right in with no fuss. Driven it 100 miles or so and no issues.
 

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That's good news.

I don't have electronic keys on this '05 limited so no programming needed I guess?..?? . . . I think the ECU's only need to be reprogrammed if you have electronic keys, but I'm not 100% on that.
The car might not have the immobilizer keys, but then there's the keyless entry remotes (fobs). I think they involve a different module (the BIU) as far as registration is concerned, and if they work now then that is the case.

Another issue that comes to mind is whether or not the replacement ECU has the reprogramming updates that were applicable to it. That might require a dealer to check with the Subaru Select Monitor.

As noted earlier, that is an odd failure. Is the car a 2.5 turbo, or non-turbo? If non-turbo, is the sub-fan relay the one Subaru supplies, or an aftermarket replacement. If aftermarket, I'm wondering if the relay damping resistor on the energizing coil might be missing (or if original relay, it might have failed), and that led to voltage spikes, damaging the ECU switching circuit. (See this post which relates to the same model relay that's used for the AC compressor clutch.)
 

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May not be related... but my 2006 had a RECALL for the ECU related to the fan-relay circuit. If the incorrect relay was installed (one without a diode to protect from voltage spikes) the output of the ECU driver transisters could get damaged.

As I remember, that RECALL for this problem covered several years of Subarus. The recall entailed replacing the ECU and several relays. I never had a problem with radiator-fans again after the recall was implemented.

As an electronic engineer, I recognize this as a problem with Counter Electromotive Force (CEMF) which is present when powering ANY coil. (such as a relay or solenoid) When the voltage to the relay-coil is released, a voltage-spike is created as the magnetic field collapses and goes all the way back to the ECU driving transistor. A relay WITH DIODE will safely short the voltage spike to ground instead of sending it back to your ECU.

Modern ECUs have a diode INCLUDED in the ECU driver circuit so there is no need for special relays/solenoids with diodes.
 

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Discussion Starter · #7 · (Edited)
It's a NA engine. It's a 2.0 JDM engine actually. Blew the 2.5 a couple years ago. The 2.0 is fine for my daily driver with 335k miles on it. JDM motor only has 60k on it. Pretty sure ECU failed when a friend of mine was poking around in the relay socket with a jumper wire to test the fan and put 12V across the ECU transistor instead. He has a r134a equipment and tank and said he could fix my AC. That didn't work out...ended up buying cheap Harbor Freight tools and becoming an AC repair guy... Fun to know that stuff now I suppose. Car needed a thermal expansion valve and relay for the sub fan. Only threw the error code after he poked around on the relay socket.
I'm curious if the new local auto parts relay has a flyback diode for the inductive kick?? Gonna try and take the cover off and see. The old one did have a diode. They could put protective snubber diodes on the ECU, but it's better design practice to put it right at the coil so I get the reasoning. They could also use higher voltage rated transistors on the ECU, but that adds pennies to the cost. It's all about shaving pennies...
I'm 99.9% sure this rare P0692 failure is from human error poking around that relay socket. Oh well...wish I knew what that transistor is. Likely a darlington pair. But does it have a built on base resistor? If I poke around the board I can probably figure this out, but the board is conformal coated which doesn't help. I bet any 40V rated 200mA darlington pair transistor would work. It's a sot89 package and they all share the same pinout.
Anyway, the key fob and everything work fine. Probably BIU related as mentioned.
 
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