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Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53168
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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I own a 2009 300E and I am having an electrical problem. The

Customer Question

I own a 2009 300E and I am having an electrical problem. The battery has been replaced three times and the mechanic tells me the problem is fixed but after running well for several months, one morning I will try to start and it will not. The clock goes crazy and runs backward which is strange, does it mean anything\/
Submitted: 1 year ago.
Category: Mercedes
Expert:  Marty replied 1 year ago.

Hi, the clock running backwards is just an indication that the battery voltage is low. It sounds like you have an intermittent parasitic drain on the system. Electrical drains can be very difficult to troubleshoot if they are intermittent. The shop will need to perform a parasitic drain test on the electrical system to see if there is too much drain on the battery when the car is off. A diagnostic test with the Mercedes Star Diagnosis tester may turn up some codes or events that will point to the problem. The car should have less than a 50 milliamp drain on the electrical system when everything is turned off. If the drain is more than that it will eventually kill the battery.

Let me know if you have any questions.

Marty

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