This is the identical problem to Ghanch back on the 21st April 2018.

One day the car works, the next nothing. If Ghanch reads this, did you ever get the problem solved?

But I continue for the sake of other readers.

Both key fob (both new battery), opens the car central locking and all 4 indicators flash. Hold down either lock or unlock button and the windows bleep. The boot opens. Press the Start Button to enable the accessories, nothing. Put foot on clutch to enable full ignition, nothing. Removed the battery to reset the ECU nothing.

So far I have tested: Clutch pedal switch with a circuit tester and it works fine. I have replaced the Start button, I have replaced the Blue Ignition relay. I have now replaced the battery. Still car is Dead. I have tested every fuse available. 2 fuse boxes under the bonnet and 2 footwell fuse boxes. I have recently noticed that when opening the drivers door the dashboard warning light does not illuminate, yet when opening any other door it does. Does anyone know anything about this? I have contacted Lexus UK who told me to talk to my dealership. They knew nothing. Surely this problem is quite obscure and unusual so someone somewhere will have some understanding of what's gone wrong: and a solution.

 

Not sure if this is similar to what you have, but check for power at these relays. USDM 06 IS250

 

Wow! That's super technical and I am sorry to say way beyond my skills and abilities.

 

If you decide to, we can spend a bit of time trying to figure it out. Only issue would be my info is limited to USDM makes and models up to 2012.
If you have 1 of these handy, you could work on the electrical system in your car and home with a little guidance.

 

Thanks for the offer. I am currently following another forum and awaiting a part to arrive. If I may, if the current investigation fails can I come back to you?

 

We are always here....

 

my 2011 is 350c has a ignition problem too. Sometimes not always, when you first start it the break petal is hard and the dash lights come on but does not start. After about 3 tryes it starts.

 

Check the plunger on the door. It's probably not making contact. There is a thread about this for it. I think they just shimmed the sensor to make contact. Then the light should illuminate once again.

 

Get your battery load tested at any local parts store. Then I would inspect the ground cable to chassis for corrosion on the body. Makes sense while battery is out. Also do you have grease on the battery terminals? It could just be a bad connection.