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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 28250
Experience:  Over 15 years experience as a Mercedes dealer technician
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I have a 2002 MB S430 and the key won't turn the ignition.

Customer Question

Customer: ***** *****. I have a 2002 MB S430 and the key won't turn the ignition.
JA: Thanks. Can you give me any more details about your issue?
Customer: the last 2 mornings when I went out to my car, I unlock it with the key fob, get in and attempt to start the car. The ignition is locked and I can't start it. I also no longer can unlock or lock the car with the key fob. I tried my spare key as well and got the same thing. Yesterday, I drove to work in my wife's car. Came back to the house around noon and the car started right away. Drove it back to work and drove it home after work no problem. This morning, same thing. Could originally unlock the car, get in but the ignition wouldn't turn. Locked. Tried both keys again. No luck.
JA: OK got it. Last thing — JustAnswer charges a fee (generally around $18) to post your type of question to Mercedes Experts (you only pay if satisfied). There are a couple customers ahead of you. Are you willing to wait a bit?
Customer: sure
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Submitted: 1 year ago.
Category: Mercedes
Expert:  Pete replied 1 year ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

The first thing to check here is to have the battery tested to see if it has an intermittent fault like a bad cell that is acting up intermittently causing this issue here.I have seen this occur before and had to replace the battery.Inspect and make sure the battery cables are all o.k. as well with the cables not being loose or corroded in any way.

If these are o.k. I have seen issues with the Rear SAM control module/ecu that may cause this issue as well as the electronic ignition switch (EIS) that can fail or act up intermittently causing this as well.The fault codes will need checked using a scan tool or dealers SDS machine compatible with this model to see what codes are set and then from there the codes can be diagnosed to locate and repair the fault here.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 1 year ago.
Could it be an issue with the key fob?
Expert:  Pete replied 1 year ago.

Usually if you have two keys/key fobs acting up the same way this isnt the key or key fob at fault here.If it was usually it would only be one key/key fob acting up and not both.

This fault here sounds to be an issue with the Rear SAM or the EIS (electronic ignition switch) itself as I have seen these fail and cause this fault here needing replaced for this issue.This will have to be tested further to be sure then the affected component replaced to correct this here.

Let me know if you need anything else and feel free to rate my help.

Thanks Pete