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Hello everyone, I'm new here and have been a huge fan of the 98-2000 LS400 since I got my first one senior year of high school 2017. I know many people don't like the face lift model but it's the only one I like lol. With that being said I also know pre-face lift models have more ECU problems than the latter. There isn't as much information about symptoms of ECU failure for 98-2000 so I wanted to create this thread for anyone who has had symptoms to share your experience. I'll share mine below.
So, I bought a 2000 LS400 about a month ago and it has been misfiring on cylinders 1,3,5,6,&7 since I bought it. The transmission shifts great and the engine sounds good as well and I drove it about 30 miles back home when I bought it. Even with it misfiring, the car still performed exceptionally well. So far I've replaced spark plugs, valve cover gaskets and tube seals, intake manifold gasket, starter, knock sensors & harness and spliced some connections on other parts of the engine harness, the coolant bypass gaskets in the back, vvt solenoids, pcv valve & grommet, vacuum switching valve under the intake, vacuum hoses and every connector in all of these areas. It's still misfiring so I've ordered the proper caps from digikey and mouser and I'll have my friend who's been an electronics technician for 30 years look at the ECU and let me know what's the issue. I will update you all when I get the ECU back. Also the A/C doesn't work which could be because it has no freon, other A/C components are bad or it's related to the ECU. I believe the car also went into limp mode for a few seconds and when I'm near a complete stop the brakes seem like they're locking up then they unlock a second later. These are all my symptoms, what are yours?
actually the facelift models are the most desirable 98-00, but the 95-97 have my heart (since i owned one in the past)! speaking of, you are right pre-facelift models are more susceptible to ECU failures (95-97), and 1st gen 90-94 have the highest/most common of ECU failures, per the ECU thread.
in my many years here on CL, it's very rare to see 98-00 ECUs fail so this thread will help uncover recent encounters with it being 2025 now. if you're in socal like me, the recent dry weather (and subsequent fires) could take a toll on old electronics and cause further issues.
as for your constant misfiring, are they the same cylinders you indicated? 1, 3, 5, 7 are all on one bank (driver side) so it might be a compromised wire on the harness. you mentioned "spliced some connections" - what are those?
Oh wow, most people I've encountered prefer the older models.
Yes you're right, I believe when these cars sit for extended amounts of time they tend to develop problems as well. I believe mine sat for about 4 years before I purchased it.
Yes they are the same one's I indicated - 1,3,5,6,&7 and idk if its wiring because the misfire has went from all those cylinders to just 5&7 then they all come back. I've switched coil packs as well. I did see a lot of carbon on cylinder #7 spark plug and I just replaced them all 2 weeks ago and have just been cranking the car for like a week so idk why it's got so much carbon or black soot.
Spliced connections are where I connect new wires where some have been frayed. Maybe I'm using the wrong term for it but I think you'll understand.
Hello everyone, I'm new here and have been a huge fan of the 98-2000 LS400 since I got my first one senior year of high school 2017. I know many people don't like the face lift model but it's the only one I like lol. With that being said I also know pre-face lift models have more ECU problems than the latter. There isn't as much information about symptoms of ECU failure for 98-2000 so I wanted to create this thread for anyone who has had symptoms to share your experience. I'll share mine below.
So, I bought a 2000 LS400 about a month ago and it has been misfiring on cylinders 1,3,5,6,&7 since I bought it. The transmission shifts great and the engine sounds good as well and I drove it about 30 miles back home when I bought it. Even with it misfiring, the car still performed exceptionally well. So far I've replaced spark plugs, valve cover gaskets and tube seals, intake manifold gasket, starter, knock sensors & harness and spliced some connections on other parts of the engine harness, the coolant bypass gaskets in the back, vvt solenoids, pcv valve & grommet, vacuum switching valve under the intake, vacuum hoses and every connector in all of these areas. It's still misfiring so I've ordered the proper caps from digikey and mouser and I'll have my friend who's been an electronics technician for 30 years look at the ECU and let me know what's the issue. I will update you all when I get the ECU back. Also the A/C doesn't work which could be because it has no freon, other A/C components are bad or it's related to the ECU. I believe the car also went into limp mode for a few seconds and when I'm near a complete stop the brakes seem like they're locking up then they unlock a second later. These are all my symptoms, what are yours?
In case of a 98-00, usually the problem starts as Silos has informed us. When the ECU begins to fail, you'd notice AT related problems first. Due to the better performances of newer ceramic capacitors used in parallel with QAS capacitors, the high frequency ripples are absorbed by them and QAS capacitors are helped to extend the lifespan. But those electrolytic capacitors still contain QAS and the lifespan is shorter than conventional ones.
Yes I read both of those threads. I bought the car with these problems so I can't say what started happening first. I do know the car went in for transmission work and they also replaced the engine and it sat for 4 years because the owner never came back for it and then someone else bought it and I bought it from them.
1998-2000 LS400 ECU Symptoms
