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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4317
Experience:  Qualified Mercedes Benz Diagnostic Technician - 20+ years experience - Workshop Foreman for Mercedes
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I have a 2005 Mercedes E320 CDI. I have replaced both batteries

Resolved Question:

I have a 2005 Mercedes E320 CDI. I have replaced both batteries with OEM equipment from Mercedes. I peridocally have a battery fault to return the car to the shop. On several occasions the car will not engage the starter. I have had this car in the shop on numerous occasions for the same problem but nobody can fix the problem. Can you give me some advice?
Submitted: 7 years ago.
Category: Mercedes
Expert:  MB Paul replied 7 years ago.

When the starter does not turn does the key turn ok to the start position?
Can you hear any clicking from the engine bay (starter solenoid)?
Does the engine fan run full speed by any chance when it does not start when turning on the ignition?

Could you also post your VIN number please.

Best regards, Paul
Customer: replied 7 years ago.



The key turns OK to the start position like it supposed to.


I don't hear any clicking from the starter solenoid.


The engine fan runs full speed while I am driving, but not when I have a failure starting.



Expert:  MB Paul replied 7 years ago.
Hi Mike,

The problem is that it is very difficult to diagnose a problem like this unless you can test it in a failed state.

To give you an overview of what happens - the Electronic Ignition Switch sends a data signal to the engine ECU which then forwards it to the drivers front SAM control module which finally outputs a voltage to the starter.

To test you would need to check for voltage output to the starter when it is not starting to see if you have voltage present - if you do then it is a faulty starter, if not then it could be any of the above items that would need diagnosing with STAR diagnosis connected to see which modules are sending/recieving the start signal.

I would check the connectors to the starter motor as I have known connection issues here causing problems.

Sadly I have known problems with the EIS, engine ECU & front SAM so any are a possibility.

Really it is a case of having the vehicle tested repeatedly with the diagnostic equipment connected to see what is going on when it fails.

Best regards, Paul
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