"I have a 2003 E Class 500 and yesterday I stopped and got some gas and shortly after while on my way home the check engine light came on and I notice the engine started sounding chopping and shortly
the 2003 E500's have known problems with the Crankshaft Position sensor and/or camshaft position sensors. The Crank sensor is cheap but a bit tough to access, the cam sensors are more difficult. Also make sure you did not put in the incorrect grade of gasoline. Mercedes engines (particularly V8's) are tuned for 91 octane or higher gas (premium). If you put in 87 octane (regular) the car will not be able to pull enough timing to compensate for the early detonation of the fuel and will misfire and run rough.
It happened to me too and I was asked if I left my engine running when I gased up- yes I did. The garage told me that mercedes sensors are so sensative and the gas cap sensor when fueling with the engine on triggered the check engine light to come on. You have to have a coding device deactivate the check engine light to go off
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