1997 LS400 won't start, possible immobilizer issue?
 

Hello. I'm working on a 1997 LS400 that randomly died and will crank but not start. I verified that the ECU fuses/relays are good, but my snap on obd2 scanner will not communicate with the ECU. There is no CEL when the key is in the on position. I had the ECU rebuilt by a company in Florida, but I still can't communicate with it. Any ideas? The central locking is a bit wonky, and I've tried to close/lock everything, but I can't get the "Security" light to come on at all. Maybe the immobilizer/anti theft is activated? Help!

Welcome to Club Lexus.

Do you have the remote FOB for the car? This is the proper transponder key?

1. Lock the car using the key in the driver door key cylinder.
2. Confirm that the security light is on-off.
3. Insert key into driver door key cylinder to unlock.
4. Insert key into ignition cylinder start car.

Other tests would be to roll window down and lock car with the key. Reach in unlock door and open the door. If the alarm is armed, it will be set off. Deactivating it is by inserting key into driver door key cylinder and lock-unlock. The alarm should be disarmed.

What was wrong with the prior ECU?

97 was the first year with immobilizers, if they reprogrammed or reset the ecu rom at all then you'll need a dealership with flash tools to code your key to it.

I can't get the security light to flash, or the alarm to sound. I don't have a key remote, just a plain key. I thought the ECU was fried because my scanner couldn't communicate with it and it seemed to be a common problem.

I will find out if they reset the ECU when it was rebuilt, thanks!

Anyone else??

have you tried the ignition sensor and some wiring by the ecu that's a problem i had with my ls 400 94

My security alarm is not working,The light is not coming on with the remote or when I use the key.So the car will not start.

Long shot but did anyone find a fix for this because I'm having the same issues and then some. Thanks

Welcome to Club Lexus.

What are some of the other issues? If you plug in a code reader is it able to communicate with the ECU?

So what did you do to fix problem!?

Thank you. I couldn't find a introduction page for the LS400 so just commenting in here for assistance.

The issues are no drivers side door lock key cylinder, check VSC, brake wear and MIL come on in display. No codes present, around 50-60 seconds MIL light goes off and loses connection with scan tool. Vehicle has original ECU and spare "good one" apparently which I haven't tried. Security light goes out after inserting key and turning to ON position. I purchased factory service and wiring manuals for the vehicle and have checked some of the engine immobilizer circuit which has low voltage. I picked up this car from someone who couldn't get it running. Owner before him sadly slammed the car on coilovers, tore a bunch of wires in the left drivers side wheel well and the vehicle shut off and hasn't run since. Owner before me shot gunned parts at it and replaced fuel pump, alternator, starter, cam and crank sensors.

Harness was repaired with solder and shrink wrapped. Currently all fuses are working in engine bay and the junction block, haven't checked all relays. Vehicle cranks, no start, no fuel pump priming, or spark. Tries to start with starting fluid but doesn't turn over. Car is a 2000 LS400 trying to save it from junkyard and daily it. Thanks.
*Solved: 10A ignition fuse under the dash caused all these issues.
Solved