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My 2001 mercedes stopped starting, the key fob would start the car intermittently then stopped working except locking and unlocking doors I thought it was the batteries but I changed them.

I have to disconnect the cable for it to start. everything seems to work after starting.but if I turn it off i have to disconnect again, any suggestions would be gratefully appreciated, thank you in advance..

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    Welcome to the site @LoriGibbs. Are you saying that you gave to disconnect and then reconnect your negative battery terminal for the car to start, or that you disconnect it and leave it disconnected? – GdD Nov 16 '18 at 8:48
  • hello, I disconnect it for about 30 seconds then connect it and the car starts with no issues. thank you for replying. – Lori Gibbs Nov 17 '18 at 22:20
  • One more interesting fact.when I turn the key on to start it the gauges all intergize except the temperature gauge thats how i know my car wont start because it wont move then i take the negative cable off for 30 seconds then the gauge moves and the car starts, seems like it has something to do with it any thoughts? i really appreciate your time. – Lori Gibbs Nov 17 '18 at 22:59
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This sounds like a computer or sensor driven problem to me. Modern cars have engine management and powertrain management computers, when you disconnect the negative battery terminal you cut off power to the ECU (Engine Control Unit) and PCU (Powertrain Control Unit) and they reset.

The question is why a reset is fixing the problem:

  1. A computer is faulty: resetting causes it to work again. Solution is to get the faulty computer repaired or replaced
  2. A computer has detected a fault which means the car should not start: If there's a serious problem somewhere the computers may be doing just what they should - stop you from driving. Resetting the computers clears the error, which gets re-detected next time the car is run. This could be a real problem or a sensor malfunction. If this is the case I'd expect to see the check engine light come on and stay on

There's a good chance that your car may know what's wrong with it and can tell you. Modern cars have OBD (On-Board Diagnostics) ports that you can connect to and read error codes. If there's an ECU malfunction, error condition or a sensor problem it will tell you. Many auto parts stores will read them for free, you can also buy readers cheaply these days if you want to read them yourself: bluetooth ones can be had for $20 and interface with free phone apps. You would want to first clear your codes (be sure to read and note them down before you do for future reference) and then read the codes after the problem happens, don't disconnect the negative battery terminal until you do!

The OBD ports on mercs are usually under the drivers side dash, close to the steering column.

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  • I did have it checked out with a mercedes diagnostic and the gentleman told me all the computers were fine my engine light has never came on and it passed smog. when i bought the car it was flooded in the passenger floor board it rained that day and thats when the car started acting up. I did totally dry it out, thats when the problems start intermittent starting,it would start right up in the mornings the after driving for 20 minutes and stop the car, it wouldnt start right up i would have to turn ignition on then off then on . then that stopped working. I should have brought this detail up. – Lori Gibbs Nov 21 '18 at 6:10

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