williamb82

i used ATE as i read reviews here about them doing good work repairing clusters and recalled reading a review of them repairing another ls400 ecu. if your caps are leaking, having them changed will help, but if there are other issues, then it wont. my ecu had other issues obviously. this one seems pretty good so ill change the caps if i find another ls to put my engine in, or if someone buys the car to fix it ill give them the caps with it for the cluster and ecu.

lex8000

I have an update on my ECU. I think my problem is fixed. I had my battery tested and they're saying it needs to be replaced (~440 CCA). THe reason the issue started now is the car is normally driven 10 miles nonstop twice daily and the last couple of weeks it's been sitting around waiting for the ECU.

zukikat

That's what I was afraid of... Definitely good to know!
I fixed my dash cluster's lighting problems with like $10 worth of parts from radio shack instead of the sending my cluster to one of those expensive repair services and it has only been about 6-7 weeks since then but there hasn't been a single lighting problem since.
I looked at the capacitors in the 50142 ECU that came in my car when I bought the car and flaked days later and they don't have leakage puddle stains on the circuit board but there's no way to be sure a capacitor's still good without an expensive tester so passing a visual inspection doesn't mean they're not bad.
I suspect that in addition to those capacitors you might actually find bad solder joints that have gotten intermittent from related temperature cycles and circuit board flexing and expansion/contraction over the years just like the inevitable Code 42 speed sensor signal issue in all of the MkIV Supra odometer units from failed solder joints, among others...
There are just so many solder joints in an ECU that without a circuit diagram, which I doubt Toyota would release, or a thorough understand of EFI design and control systems which I don't posess myself, good luck figuring out where to begin...

Glad someone found your problem.
The computer typically won't make the engine cranking hesitate and then go back to normal, nor should a internally leaky power steering vacuum valve which would normally cause an unexplainable loss of steering fluid and some tailpipe smoke, but a weak battery with low voltage can cause all sorts of strange behavior.
Most diag codes typically list a few steps to check and if those steps all come up proper then the final component listed to check is sometimes the ECU but I don't remember any codes on OBD-I and prior Toyota ECU's that point directly to the ECU as the problem. Plus it seems that in the LS400's that have ECU failures they usually either say nothing's wrong at all or won't even respond to the diagnostic jumper when you try to read the codes, at least that's what mine was doing with 2 different ECU problems that rendered the car pretty much undrivable at random...

The challenge with diagnosing ECU issues is that my car would go from totally normal to very unhappy at random with no warning and no codes and I couldn't afford to be stranded with my long work commute. I test drove it 150 miles non-stop on the interstate with no problem and then days later it went from fine to unhappy and back with no codes so I replaced the ECU and the drivability issues went away.

When you say random shut-off, was it just the engine shutting down like you turned the key off or did the whole car go dead, gauges and all, go dead. If it was just the engine I'd be at least slightly suspicious of the ECU. If it was gauges and all, then it's more likely a power/battery/alternator issue.

lex8000

The engine just shut off going 60 a couple months ago. Pulled over, restarted and it ran fine. Then a few weeks ago it started rough in a high gear, rough idle and all that. Now with the new (used) ECU it appears to be working fine. The only thing is that it worked fine with the old ECU after he reset it twice. At this point I think it was an ECU on the way out, hence the intermittent problems. The slow to turnover on start problem was a battery problem unrelated to all the other stuff.

That's what I'm hoping for at this point anyway . Thanks for the info.

zukikat

Sounds about right. That's each of mine's two ECU related problems almost to the letter.
On the ECU that was in my car when I got it, it would get to a point where it wouldn't even reset for 20-30 minutes, pull the fuse for like 5 minutes and reinsert it or even disconnect the battery for a few minutes and reconnect it and the CEL would be right back on again, and then if I just walked away for 1/2 hour or so and tried the key again the CEL would finally be off again and the car would go back to behaving normal on its' own for a while again 'till the next random time it decided to flake, sometimes hours later, sometimes not for days... Cold weather seemed to make it worse too. I suspect that yours would've slowly begun doing either or both of those things more and more frequently as time goes on... Hopefully the used ECU is more healthy and it sounds like it is. Mine definitely is although I really don't like its' management of the transmission compared to the other one but at least it "runs and drives" normal again...

On a couple of other similar era Toyota/Lexus vehicles I've also seen a battery in the early stages of a shorted plate cause a car to die with no warning but the gauges and everything typically went dead too in that case when I encountered that which is why I asked about gauges lit up and working or also dead at that moment...

lex8000

Good info to know. Thanks.

At this point the big question is the replacement used ECU healthy or not? Tim will tell .

zukikat

Yes, time will definitely tell.
I suspect that they're all in varying states of tired at their age with some still totally happy and usable for a good while longer, some just slightly flaky, and some basically useless at this point, but I'm only guessing...
But they're cheap enough used that having a spare or two laying around and testing each of them in the car for a month or two as an emergency spare seems to be a very practical "just in case" option until a true solution can be found.
Plus even if it's a used one, if your original was flaky and the used one runs the car consistently and normally as a daily driver without threatening to leave you stranded then I wouldn't worry about it 'till the used one starts showing signs of becoming intermittent too.

I'm not totally satisfied with the overall behavior of the used ECU that's running my car now but it's been running errands and doing my 100 mile round-trip work commute along with numerous personal trips into the city for over a month reliably with no complaints or intermittents so far, in style and comfort, and that's what really matters...

I'm frustrated that this is such a common issue with these cars but I still like my LS...
It's no Twin-Turbo Supra but it's definitely an excellent work commuter vehicle and road-trip car for sure! Just keep a ratchet and a spare used ECU that you've personally tested in a box in the trunk and you're totally good to go cross-country any time.