I have 2000 LS400.. Car will not start....Security light stays on when you try to start...Had key check out...key was okay....Could ECU be bad...

 

Does it turn over? if it's not turning over then it's not an immobilizer issue. The immobilizer on '98-00 cars kills fuel and/or spark, not the starter.

If it's not turning over you need to look at the starter fuse, relay, fusible link, battery terminals, ground wires, and the starter itself.

 

It may be your starter , does it knock at all at when you start it up ?

 

Yes. Car turns over starter good..fuel pump good.. fuel pump relay circuit ...No power there...

 

That's my problem. ..Fuel pump circuit is not hot...would security light have anything to do with not starting its steady blinking when I'm trying to start car will not cut off

 

PureDrifter just stated that the immobilizer cuts fuel. the security light should turn off when the key is inserted.

 

That's my problem. ..Fuel pump circuit is not hot...would security light have anything to do with not starting its steady blinking when I'm trying to start car will not cut off

 

Light isn't cutting off steady blinking when I insert key

 

Immobilizer located

 

then it's an immobilizer issue and you aren't using the right key. If you are using the right key (ie- one that's KNOWN to have worked with the car) then it could possibly be a immobilizer ecu/amp/sensor problem, but generally those will throw a check engine light.

 

The continuous blinking after inserting your key means that the RFID signal from it is not recognized by the system. The transmission and the reception is done between the transponder and the key. The RF signal from the transponder reaches to the key and the key responds sending specially formatted bit streams. The transponder receives the streams and forward them to the ECU. Sometimes the communication between these are not well done when some unusual object is attached to the key or when you are at a location where very strong EMI (Electro Magnetic Interference) exists.

Is your key attached with something?
Is your location EMI free?

If not these, and the key itself is OK, then the transponder attached to the key cylinder, the ECU or the cable between them should be checked.

 

don't feel all alone, I just finished replacing the transponder ring in a 1996 Acura RL, same symptom as you had!

 

Where's E.C.U. Located on LS400

 

Behind the glove box on the right side of the car. The following posting has some instructions on how to take out the ECU :

https://www.clublexus.com/forums/7627322-post160.html