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Marty, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 54840
Experience:  Bosch Certified Master Technician with over 35 years experience in the automotive industry.
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I have a 1998 R129 SL320. The car came with 2 keys only one

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I have a 1998 R129 SL320. The car came with 2 keys only one of which works. I ordered a new key from MB but although it was the correct key it would not unlock the car. I assume at some stage the immobiliser has been reset and the non working key and the new key are probably the some code but the working key is different. Any advice on how to get two working keys?
Hi, you can try synchronizing the keys by pointing the key at the rear view mirror and press the lock or unlock button two times then insert the key into the ignition and turn the key tow position 2 (second click). Remove the key and see if the remote is functional. Let me know how you make out.Marty
Customer: replied 1 year ago.
No luck I am afraid, I have also swapped the batteries between my working key and non working one in case the batteries are flat. As the car is now 18 years old I am afraid I don't know its past history other than it does have a full MB service history
I have had brand new remotes come programmed incorrectly from Mercedes. I would first take the car and both remotes to the dealer and see if they can code the remote with the Star Diagnosis tester. If they have no luck I would suggest they order you another remote. Since you have one remote that works and the new remote will not synchronize to the car it would have to be defective.
Customer: replied 1 year ago.
Marty, just picked up last night's email. I assume this is not a particularly big job to do. I was not sure the staff at MB Guildford really knew what the problem was when I tried to get the new key working. I obviously don't want to spend a load on an old car that is of relatively low value
Anytime they connect the car to the Mercedes tester you can expect a 1 hour labor charge. I would expect no more than that. If they sold you the key I would expect them to synchronize it for you for the standard charge and also to order a replacement if they are unable to synchronize the key and then sync it at no charge the second time. One last thing that you could try before going to the dealer is to point the remote at a receiver and press the button two times then insert the key into the outer door lock and lock and unlock the car. If you have no success it will need to be connected to the Star Diagnosis tester.Let me know if you need anything else.Marty
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Customer: replied 1 year ago.
thanks for your help and advice. I'll try the key in the lock technique tomorrow.