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This procedure worked on a 1996 LS400 which I understand is fitted with a Scorpion 5000 alarm/immobiliser system, this being fitted in 1996 by Lexus in the UK, before sale. I don't know if it was fitted in other model years.
The Scorpion 5000 alarm system can apparently be identified by the remote control fob, which has two buttons. The black one sets and unsets the alarm and central locking, the red one sounds the alarm immediately. On the the right is a slide switch and on the left is a three pin socket. Pictures are attached.
I gleaned this information after much research on the internet but cannot say whether it will work with other years or similar alarm systems.
My friend's car had been unused for 3 years, so had a flat battery. After replacing the battery the car refused to start, and by a process of elimination I figured the immobiliser was the most likely suspect, judging by the number of times the topic comes up on the internet.
I ended up with 8(!) possible ways of resetting the immobiliser, but luckily this one, the first I tried, worked:
1. With the battery connected turn the ignition key to the accessory (first) position
2. Disconnect the earth (-) cable from the battery
3. Turn ignition key to the on (second) position
4. Reconnect the earth cable to the battery
5. Turn the ignition key to the off position
6. Remove the key
7. Close all doors, boot and bonnet
8. Lock the car, using the remote control fob
9. Unlock and start the car
My friend's car started immediately, after a 3 year "rest".
