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Key not working, HELP!

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  • Key not working, HELP!


    I have a smart roadster Coupe 2004 only ever had one key and now I am having issues. It started with the key having a very weak signal, i had to be very close to the car for it to lock/unlock so i though it was the battery in the fob. I changed the battery in the fob but this made no difference.

    Now the fob does not work at all, no 9 flashing lights on the indicators or anything. Press any button, lock/unlock/boot no response at all. If i disconnect the car battery (which is new and tested so not the issues) and re-connect after 10-15 mins the fob works fine. But if i park up, leave the car for 30 mins the key is dead again. So i have to repeat disconnecting the battery to make it work again.

    Has the key gone out of sync and need re-syncing, but why would the key work after disconnecting the battery?

    Any help would be great as my wife is really keen on me getting rid of the car and this could be the last nail in the coffin

  • #2
    The receiver unit for the keyfob can fail from moisture ingress, especialy on Roadsters, and cause the symptoms you have seen. The receiver is located under the centre tunnel plastics, just below the handbrake (looks like a large automotive relay).

    Does a spare key show the same behaviour?
    Last edited by mikerj; 03-12-18, 12:28 PM.


    • #3
      Thank you for your response! Do you know if it is an easy fix and would the part be easily available/where is the best place to go to get the part?
      Why would disconnecting the battery resolve the issue temporarily if it is the receiver?
      I only have one key and from reading through different forums I know this is very dangerous with a smart, so think I will have to get a spare ASAP. (If i get this resolved)


      • #4
        It's fairly easy to replace the receiver, it doesn't require any coding etc. it's just a case of getting access which means either removing the plastics in the centre, the seats and carpet or just removing the plastics and cutting a slit in the carpet for access. I have no idea how much a new receiver would be, but s/h parts are easily available through eBay etc. though they are often listed as "key relay" or "immobiliser relay" rather than "receiver" so you might need to juggle the search terms to find them. That same part is used on the 450 ForTwo. Smart part number is 0003503V003.

        I don't know the exact failure mechanism, but the very small range followed by failure is a classic symptom of receiver failure (or corrosion on the connector). If it were a problem with key sync then you'd get the indicators flashing 9 times when you operated the fob.

        I strongly recommend you get a second key coded. Not only would it save you in the event of a key sync problem it can help with diagnosing issues like this. This doesn't have to be ruinously expensive, you can buy the diagnostic kit needed to sync a second hand key for about 35 (Delphi DS150 clone) if you have a windows laptop, and it will also let you read diagnostic codes and perform clutch adaptation etc. Essential for a hands on Smart 450/452 owner.
        Last edited by mikerj; 03-12-18, 03:32 PM.


        • #5
          Thanks so much for all the advice, really appreciate it. I have just ordered the part from ebay so finger crossed and will definitely get the second key if i get the car working again.


          • #6
            Just an update for anyone else that has the same issue. Changing the receiver fixed the problem, ordered the part on ebay, really quick (less than 5 mins) fix, all working now.

            Thank you for your help and advice and i will be ordering a Delphi to code a second key, hopefully it is as easy to do.


            • #7
              Originally posted by ddb87 View Post
              Just an update for anyone else that has the same issue. Changing the receiver fixed the problem, ordered the part on ebay, really quick (less than 5 mins) fix, all working now.

              Glad you're sorted. When mine had failed I took my car to n Indie who proceeded to DE-code the originally working keys. I changed the receiver after the event & then took the car to Mercedes who then just re-coded the keys to the car.


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