Thanks again Yamae. My home equipment is not what I'm used to when I service my clients. Most have binocular microscopes that allow high resolution inspection and repair but I only have a 4X magnifying glass. My analog solder station also has just failed so I need to get a newer digital one that regulates the tip temperature when trying to solder/unsolder vias attached to ground or voltage planes. I know what you mean by the effect of the ESR and ESL of the cap on stability. I have done designs where I had to use a very low ESR cap and then put in series a known low value precision resistor to stabilize because of the wide tolerance of ESR in electrolytics. My background is primarily in RF design but I also usually do the power supply designs for my customer's boards. As you know the temperature extremes and the very wide swings of the 12VDC during cranking make automotive electronic designs difficult. Not really much difference in RF and power design just the operating frequencies, the equipment used, and, as you say, Bode analysis. I was showing my wife an area of the board last night when she wanted to see the difficulty of the repair and I see a cold solder splash across an unpopulated surface mounted cap. This may be the problem. I will report back.

Hey guys,

It is May 29, 2019, i hope the links in the 1st post on this thread still work so I can order the caps for my 95 LS. I live in Arizona, my LS has 260k and my caps most definitely need to be replaced. I currently have no a/c, no power when accelerating(like i am pulling a boat or heavy load) and CEL with no codes when scanner is plugged in. I will need to find someone here in Phoenix to do the job as well.

Thanks

Yep, everything is relatively current. I just updated my ECU (95 sc300) using all these instructions. I purchased my capacitors (2 sets) from Digikey. Caps plus shipping was about $14. Car would run for about 1 minute, then get extremely rough and die. I would wait 5 minutes, rinse & repeat. I didn't even do any significant troubleshooting, other than look into error code. After I did the update, I've not had a single issue. Have put about 2k miles on the car since.

Update. Well Yamae I replaced my old Weller analog solder station with a Hakko digital one which regulates the tip temperature and it works great. However, I'm afraid there is internal plane damage around C103. This 10 uf cap had been leaking. With C103 removed I can ring from the -via to other grounds in the area and get good continuity. I can't ring the +via to any other connection so it must attach to something using an internal trace. If C103 is part of a buck-boost forward converter or a flyback converter it is possibly attached to an inductor,transformer or a diode. A hard wire to that inductor would maybe work but I don't know what part of the power supply is associated with C103. Can you possibly identify what the +via attaches to?

I also have access to a repaired and warranted California speced '93 Lexus LS 400 ECU, 89661-50151. Will this unit work on my Fed speced '93 LS 400 (original ECU PN 89661-50140)?

My specialty is mainly about ECUs for JDM Gen2 and after. Sorry that I don't know much about Gen1 although I have fixed them a lot replacing capacitors and some other parts just doing the reverse engineering. But I haven't touched Gen1 ECUs for several years now and I don't have any references any more at my hand. In Japan, Gen1s were totally gone and Gen2s are just few now. So I have no idea how C103 is connected to the internal plane. But generally speaking electrolytic capacitors are used to remove ripples of DC lines and the negative side lead wire is always connected to ground plane or trace. The positive side to in/output lines of regulators. I hope this may help you to analyze the connection.

Regarding the ECU's compatibility, as long as the model year is the same, the California spec one usually works OK in Federal models although the engine power is a bit less.

Update to Yamae. I bought the California unit. Installed this AM and '93 LS400 immediately cranked. Short town and highway road test indicates smooth operation. I will run this one for intensive testing for the next month or so. I probably won't unseal this unit even though it may have board damage since it will be used as a backup ECU. The cost was very good. I have established a correspondence with the seller who has told me the cap PNs and they are the ones you recommended. He shared that like me, he also is having a hard time finding junk yard units that don't have board damage. He says that out of every 100 units only about 5 turn out to be repairable due to board damage. I plan to continue to reverse engineer the failed '93 ECU where the C103 part leaked onto the board. Maybe I can find a way to hard wire traces to appropriate components that will afford stability and acceptable ripple assuming other traces have not been destroyed in that area. At any rate I now have a backup for my '93 and '94 that will serve us for long trips since Jane and I both travel in one of them at a time. Now on to my instrument panel debug where the power supply for the fluorescent tube light is failing in my '93. I think there is a repair tutorial for that on this forum. Again, thanks for your help.

solder order
 

96 LS400 when soldering new caps do you solder cap in on bottom , then do top of board side? Or do you let cool after bottom, then solder top?

Soldering only bottom side is enough. Because those holes are through holes.

Thanks Yamae for the quick answer. Should you still clean and flux both sides? Is it ok to use old leaded good quality solder? or buy new lead free? Thank you for the help? Will open up ecm soon. Pretty certain this is the problem. Intermittent misfire #6,less on #4 cyl. check engine light etc.Has new plugs, wires ohm ok. no secondary leakage found? car runs fine then out of the blue it happens .

You are welcome. As long as "no clean" flux is used, you don't need to clean but what is written here would be your help.

The solder used for LS400 contains lead because Toyota had never used the lead free solder for LS400. The regulation RoHS was not yet considered at that time. You'd better to use good old classic leaded solder.

Hope your ECU board is not yet corroded by the leaked QAS liquid and your capacitors replacement will be going well. It would be nice of you if you can come back and report the results.

I was having codes P300, P302, P303, P304,P305, P306, P308 and P172 all pop up. Before I found this thread I threw new plugs, wires, and coils. Codes still popped up and car would lose rpm at stop lights and eventually stall. I ordered capacitors and took the ECU to a local electronics shop for him to solder. He fixed the capacitors and a few resistors along with the copper tracks that melted away from the acid. He had the capacitors on hand. He charged me $140 but its because he made other repairs on the board and not just solder the capacitors.

Installed it today and no check engine light on. Car has tons of power now. Thank god I found this thread. Shop is in Norwalk Ca if anyones interested.

1993 ls400
 

Hey all. I set out on doing this capacitor replacement got caps, then some time later found time to remove the ecu.
My problems are seemingly a miss fire and lack of power. the problem only shows itself after the car is up to temperature. and is especially apparent when going 75 and trying to accelerate on a hill.
I have the weird red light on with the six bars on it, 3 on each side. of which i dont know what it means. I did have an idle problem, it was always high and it wouldnt go over 80 very well. but then after replacing what could have been the original fuel filter the idle is fine now and will go over 80 but still has the missfire. I dont know if a car can run on a 26 yr old fuel filter but there was 'stuff' in it. I mean, the new one was like an empty soda can the old one had weight to it. all kinds of stuff came out of it.
I went to replace the caps today and when i get the ecu out and opened, its obvious that the caps have been replaced already. they look in good shape, you can see where the board around the 220mf 50v cap area has been cleaned. There was also a date written on the ecu of 2010 , and the cap brands are the ones in the description opposed to the ones i could get at this time.
So, could the replacements have failed? in 9 years?
And what other things can i do to find my problem. i took one plug out to examine it. seems fine, caps and rotors seem fine. And if you being an experienced lexus owner/repair person could explain any procedures in detail would be helpful.
Over time the check engine light and the trac light would go on, I could floor it from a stop up to maybe 45-50 then they would both go out. Well they arent going out anymore.
I'd like to keep the car, but its getting difficult to find exterior parts (currently i need a driver side fog lamp assy) and i dont want to throw parts at it for nothing. And when i bring it to a mechanic the 1st thing they want to do is grab their odb2 and have the computer tell them whats wrong... they find out its odb1, they dont know how to fix it.
Any help would be appreciated. I took a couple pics of the ecu. which does not really show anything conclusive. and i was entertaining making a video of the problem its having while driving. again just a miss fire. and lack of power. let me know if that would help.

The dash light with the 3 bars on each side may be a parking lamp failure.

On cars this old various connectors are now brittle with the years of heat cycling Many sensors as well may be due. Would have to check those to verify a good contact.

OBD1 cars, shorting the diagnostic terminal allows one to read the flash/error code here:
http://www.lexls.com/tutorials/intro/codereading.html

This explanation reminds me of a weak fuel pump. A badly clogged fuel filter becomes a too much load for the pump and there goes too much current to coils in the pump motor via brushes and the commutator causing extra heat. This often shorten the life of the pump motor and the torque becomes less. The pump can't supply enough fuel and you'd have power problem at higher speed.


Judging from the year 2010, the capacitors used were not correct ones. Probably those are only selected seeing the capacitance and the voltage. You'd better to use capacitors listed in the capacitor's thread.

Anyway, I'd suggest to check the fuel pump first.

My 1998 Lexus LX40 will not start. The dreaded red light shows on the dash and I've replaced the battery in my key, attempted to get the car to recognize the key but it still won't start. Over the past several months this has been going on and now just won't start. I noticed that the car loses power while driving as well.

I've decided to remove the ECU and check for corrosion of the capacitors and I've posted a photo below. I'm not seeing anything that jumps out and I thought I would let you educated minds have a look.

@Mauser has graciously offered some advice. I'm wondering if I could purchase another used ECU like this off ebay and swap it in to fix my issues? Would I need to reprogram my keys? :sad:

https://cimg6.ibsrv.net/gimg/www.clu...22b4d01ecb.jpg