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Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53981
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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Sl550 2009 does not start at all but battery works fine

Customer Question

sl550 2009 does not start at all but battery works fine
Submitted: 1 year ago.
Category: Mercedes
Expert:  Marty replied 1 year ago.

Hi, my name is***** you give me a little more information? What is the background on this problem? Does the motor crank but not start?

Customer: replied 1 year ago.
no cranking; it had slow starts this morning but started; i drove it for about 20 minutes with two stops at which point it also had a slower start
Customer: replied 1 year ago.
when i parked the car and got back to it after 15 minutes the car did not start again without any cranking; road side assistance only checked and jumped the front battery without impact. I am thinking I should have someone jump the rear battery and see if that helps?I do have as suspicion that I left the light on over night so it would make sense for it to be a battery problem.
Customer: replied 1 year ago.
thoughts?
Expert:  Marty replied 1 year ago.

Sorry about the wait I had to step away

Expert:  Marty replied 1 year ago.

It sounds like the starter battery under the hood is bad

Expert:  Marty replied 1 year ago.

The battery in the trunk could also cause the problem but it is more likely to be a bad starter battery. Both batteries should be tested. Jump starting is only done at the battery under the hood.

Expert:  Marty replied 1 year ago.

If a jump start from the battery under the hood did not help the battery in the trunk should be tested. It's also possible that there is a fault with the starter or with the transmission gear selector module. If the computer does not realize that the transmission is in park it will not activate the starter.

Customer: replied 1 year ago.
even if the rear battery is the problem road assistance would not be of any help and I would need to get the car towed? is the starter battery the one easily accesible under the hood? the mechanic checked the battery and the amp and considered it functional
Customer: replied 1 year ago.
> If the computer does not realize that the transmission is in park it will not activate the starter.I can only turn the key when the car is in neutral or park so I guess that eliminates that option?
Customer: replied 1 year ago.
are there any diagnosis tests I can run with the starter?
Expert:  Marty replied 1 year ago.

A jumper can be connected to the rear battery as long as the front battery is ok. You can connect jumpers to both to be sure. If you are comfortable with the vehicle electronics you can remove the starter relay and bypass the relay with a jumper lead to test the starter motor.

Expert:  Marty replied 1 year ago.

Click on the attachment below.

Expert:  Marty replied 1 year ago.

You will need to remove the green relay and place a fused jumper lead from terminal 30 to 87 in the relay connector in place of the relay. When you make your connection the starter should operate.

Customer: replied 1 year ago.
thank you; that is unfortunately too advanced for me; i will see if the road assistance person is comfortable in doing so; if the starter starts would that mean there is no issue with the battery and its an elctrical issue?
Expert:  Marty replied 1 year ago.

If the starter works it indicates a fault with the battery, cable connections or with the start authorization system that involves the computer and relay.