ovas

My 98 ls400 was running great until my check engine light came on for knock sensors. Replaced the sensors and got another code for knock sensors circuit. Replaced the harness again and still the same code. Decided that it could be the ECU that’s spitting a phantom code since the car would run perfect for a couple days and then out of no where get very bad gas mileage like the vvti system isn’t working and still codes for knock sensors. Got another tested ECU today same part number from the same year and make Ls400. After installing the new ECU the car will not start. If you turn the key into the ignition it makes a high pitched beep that doesn’t go away and then the abs and check vsc light turn on and car will not crank. Put old ecu back in and it’s doing the same exact thing. Yes I did disconnect the battery first. This is my daily car it will not start and I cant get a reading from the obd port no CEL only Abs and Check vsc on and loud beeping. Hoping someone has a solution for me I’m really desperate.

400fanboy

Your car is now a brick. Your car has an immobilizer and you cannot replace the ECU with one from another car. You must repair the old one - if that's what's actually broken - and put that back in your car.

While it's technically possible to reencode the immobilizer;

https://www.clublexus.com/forums/es-...apped-ecu.html

Good luck with the average person doing this.

It has an interesting point however:



However, I doubt your new ECU came with... the keys from the old car to make this trick work.

EDIT: Oh I just realized you put the old ECU back in and it did the same thing. That is... strange. I don't know what to think of that.

Losiracer2

probably screwed up the immobilizer programming, no other option but to source a paired key/ECU or get it reprogrammed at the dealer.

400fanboy

I thought [most] dealers didn't have the equipment to reprogram the car anymore and\or won't do it because of how old it is.