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Hi,
Mine is a 1994 SC300 Auto. Got it from my wife for my retirement that year. Well maintained. Only 61K. Because if the pandemic we have not gone out much and we use my wife's 2018 Subie Forester XT, the last of the turbos. Anyway, it is parked in the driveway. Unfortunately, I only had half a tank and only started maybe twice during last year.
Well, finally we had a few days above freezing so I started it. After the second try, it started but after a few seconds it dies off. If try to maintain the idle it revs up to 2-3K but drops down to nothing and dies again. If I try to keep the RPM up, it starts misfiring through the exhaust. I have trac. It throws a code 41.
I remove the TPS connector and tried to start. Nothing changes. The same thing.
Before I start following the lengthy trouble shooting procedure in the shop manual, I was wondering if anyone had a similar experience and could offer some time-savings tips.
Sounds like a bad ecu, happens with age on SC's especially on the cars that are used less like your 94 with 61k on it. they tend to dump gas when the ecu starts to have bad capacitors etc..
Another sc300 ecu for an automatic from 92-95 could help. there is a federal and california models for the ecu, if your car is not a cali car then the ecu is likely the more common federal one.
Interesting that it would throw a code 41 for bad TPS though. Did you unplug your intake air control valve or the TPS to the right of it?
On the throttle body, I disconnected the TPS. I have two of them since I have trac. I only disconnected the TPS not the secondary one. I have borth volumes of the factory service manual, and code 41 indicates a problem with the TPS (throttle position sensor). I started checking the resistance and some of the preliminary results seem to indicate it is working. I did not have a chance to check the harness.
It is very possible that the ECU needs a capacitor service.
The very specific capacitors needed to do it with the right ESD safe tools can be obtained from Digi-Key or Mouser but for the non-DIYer, Tanin Auto Electronix can still do this on special request as can Relentless Motorsports. Or you can note the part number on your ECU's metal casing and hunt for one just like it off ebay. Most early model year SC300 Auto ECUs (especially with Federal 49-state emissions) should not be too hard to find.
Either way, whether you repair your original ECU or repair a donor ECU from eBay one of them has to be repaired. The best approach is probably to send your original off for repair.
It is good to go through the troubleshooting matrix in the factory SC300 TSRM but this is a documented enough issue such that it's a pretty common repair for these cars.
Interesting that it would throw a code 41 for bad TPS though. Did you unplug your intake air control valve or the TPS to the right of it?
If you do a search it happens, couldn't tell you why it throws the tps code but when ecu starts to go there are some common codes it will throw.
Especially since plugging the tps in and unplugging it does nothing, cause the car would start fine with the tps unplugged and the tps code, however, it would not rev cleanly there would be a stumble off idle but it would still start and run.
Originally Posted by KahnBB6
It is very possible that the ECU needs a capacitor service.
The very specific capacitors needed to do it with the right ESD safe tools can be obtained from Digi-Key or Mouser but for the non-DIYer, Tanin Auto Electronix can still do this on special request as can Relentless Motorsports. Or you can note the part number on your ECU's metal casing and hunt for one just like it off ebay. Most early model year SC300 Auto ECUs (especially with Federal 49-state emissions) should not be too hard to find.
Either way, whether you repair your original ECU or repair a donor ECU from eBay one of them has to be repaired. The best approach is probably to send your original off for repair.
It is good to go through the troubleshooting matrix in the factory SC300 TSRM but this is a documented enough issue such that it's a pretty common repair for these cars.
Hi and thanks so much for your advices. I agree with you that the culprits are the electrolytic capacitors. 27 years under occasional wet conditions (under passenger's wet boots) is enough to cause leakage. I should know, I am a ham radio operator.
I am in the process of removing the ECU. I am stuck on the third connector. I would appreciate your letting me know how it opens up. Interestingly, mine is a CA model even though I bought it new here in New York. ECU 8961-24333 175000-6330 12V DENSO 40P 08/1993-01/1994.
Again, thanks.
Well thanks Ali SC3. It worked!. And to be sure, the problem seems to be in the ECU circuit board. Specifically, a capacitor was leaking badly. I removed it and I am trying to cleanup the black residues. I cannot yet tell if the traces were damaged or not. The electrolytic cap is a 63 V 47 uF one. I'll have to order a replacement one with a low ESR. The saga continues.
Problem fixed. I had to repair for traces that were broken and replace the cap. All done. I replaced the ECU and the car runs like the day I bought it 27 years ago. I followed an excellent video on how to repair a circuit board. Incidentally, my radio was not working. Now it works fine. Thanks for your help guys!
Hi. Thanks. I tried to get schematic for the ECU, but I understand they are not available. I was told to reverse engineer it. The leaking cap corroded four traces, two heavy ones and two very thin ones. See pic. I followed an excellent video on how to repair a circuit board. I did not have a microscope but I have a strong magnifying glass. I very gently scraped off the coating on the traces until copper showed then use the right size wire to by-pass. Checked it for continuity with an ohm meter. On of the heavy traces was to connect the negative of the cap. Since the trace started above the positive one, I just turned the cap around and soldered there. When I finished I coated everything repaired with a green paint that cures with UV light so I just put it under the sun for an hour. Since one of the repair was for the leads of the cap, that leaves one heavy one and two thin ones. Unfortunately, I don't know which is what without a schematic. I was going to sweep the connector pin in the housing but I was too excited to try it and just installed it. For sure, one of the four broken leads belonged to the radio.
is there a proper diy somewhere for recapping the ECU for the SC400 specifically? like which once to use and so on. I found one for the LS but idk how well it translates to the SC
This is a follow up on the reborn radio. I checked the wiring diagram on my SC300 factory service manual (Vol 2) and I could not find any connection to the ECU. I also noticed the following: on the second trip, again, no radio. During the third trip, I hit a bump and bing, the radio came back. I suspect that there is a loose connection of the B+ feeding the HU somewhere.
Code 41
