Hello all, have an 05 R53 S with 110 k miles, I have put a ton of time and effort into the car since buying it two years ago, has been super reliable as my seasonal driver. Left to go to an appointment this morning , noticed the speedo was telling me the car was doing15 mph over what it really was, stayed at 15 even at a stop. Went to first place, shut it off left an hour later, started right up, speedo was working normally, second stop shut car off, got back in 10 minutes later, started right up speedo normal. Third stop went into grocery store came out, car was dead. Doors unlocked all the normal lights came on turned key- nothing!!!! Put obd2 scanner on it -no codes tried to jump it, no go. Push started it, fired right up quickly, no problems drove it an hour home, speedo fine no idiot lights everything normal. Pulled in garage, checked battery voltage, all good. Went to start it- nothing. Tried other key-nothing. Looking for any thoughts on what it maybe? Thanks in advance-E

 

Sounds like you may have a dead spot on your starter.

 

Since the speedometer is acting funny I suspect a low voltage issue.
Since the starter won't turn over, I suspect the battery may have voltage but cannot produce enough current to turn over the starter.

IF the battery is good, check the cables to the battery/starter/alternator. Not only visually inspect them, but use an ohm meter to make sure the cable is not corroded internally.
If they are good have the alternator tested to make sure it is charging the battery.

Hope this helps

Jeff

 

Well after some basic diagnosis I decided to install a new starter, that solved the problem, everything else fortunately is back to normal, even the speedo. Thanks for the input guys!