brianjb

The screw in my master key fob of my 2002 RX300 fell out and I lost the transponder. I have used the valet key since then. I purchased a new transponder this week, inserted it securely in my old master key case and successfully activated it. It opens and shuts the doors remotely. HOWEVER. I discovered that the old master key will not start the car. I can manually unlock the door with it but when it is inserted in the ignition the security light does not go off. The engine turns over but the car wont start.

1) Does it need the original transponder to work?
2) Can I pair it with the new transponder in some way?
3) Does the dealer have to do this?

Thanks for any help with this puzzling problem. I apologize if it is covered elsewhere but I could not find any reference to it.

JAB

Yes, what you lost also includes an immobilizer. Not sure whether you can program your car to recognize it or not; someone here must know.

brianjb

I can still start the car with the old valet key. It's the master key that doesn't work in the ignition. Works in door lock as I said.

salimshah

Jab diagnosed it right.

The shell and the cut of the key does not make it the master key. The magnetic slug's field signature makes it a master key if it is registered as such in the ecu.

Withe the loss of the slug, unfortunately you have lost the master key.

Valet key has the slug too, but for it to be a valet key, the ecu has the signature saved as valet and the cut of the key will not operate certain locks.

More information can be found in the sticky .. having problems start here sticky.

Salim

brianjb

Thank you Jab and Salim. What is strange is that I was able to use the key and shell to program the car to accept the new transponder - in the role of the master key. That's what threw me I guess. Is there some way I can get the new transponder paired with the old key? Can the dealer do this?

salimshah

I would always recommend that folks visit the dealership. You never know that the key you think is valet, may be master.

Information on the net (including my posts) may not be correct. Visit the dealership, get your vehicle washed, enjoy the refreshments and browse through the new models on the floor. . Dealers want you there.

Salim