Car will not start after washing it at an automatic car wash?

JOSERP156

MEMBER
2012 MERCEDES BENZ C300
3.0L
V6
4WD
AUTOMATIC
178,000 MILES

I took it to an automatic car wash and the lights in the picture started popping up and none of the lights for the car wanted to work. The car still drove, so I went somewhere and parked, car taillights did not want to turn off when I put it on drive or reversed, nothing was happening. I turned the car off lights stayed on came back next day battery is dead. Had someone come and check out the battery and fuses and everything was good. He went under the car and tried to start it but still nothing. He said it’s an electrical problem and it could be the fuse. Now the car won’t have any power unless I jump it.

1 Reply

AL514

MECHANIC
4,793 POSTS

Hello, since this happened after going through a car wash, then the issue is going to be water intrusion into either a connector that no longer seals out moisture anymore, or possibly if the battery box is missing its cover, or engine compartment fuse panel. I would start by checking connectors that would have been exposed to water during the car wash. Especially any under the vehicle. Also check under the driver side and passenger side low dash. Look up with a flashlight for any areas that may have leaked water in. If you find any connectors that have water in them or green, or white corrosion in them, that's a problem. Water can short out pins inside connectors, and yes can blow fuses, so it would be wise to go through all the fuses throughout the vehicle as well. Here are a couple guides to help with checking the fuses with a test light.
There is a fuse panel in the trunk of the vehicle as well on the driver's side. I would go through all the fuses, there may be more than one fuse that blew also. I'll find the exact locations of all the fuse panels for you.
But I'm almost positive these vehicles have a cover that's supposed to be over the battery. The C Class has an additional battery on the right side of the trunk (passenger side) as well.
Well, this vehicle has 5 fuse panels, Diagrams 1-3 below are the Front PreFuse Box location and there should be a cover over the Battery in this location.
Diagram 4 is the Rear PreFuse Box, it looks to be under the carpet with some type of access cover,
Diagram 5 is the Interior Fuse Box.
Diagrams 6,7,8 is the Front SAM control module and Fuse/Relay module, the SAM module acts as a sort of Body Control Module,
Diagrams 9,10,11, is the Rear SAM control module and Fuse/Relay module, behind a passenger side cover, so there are a lot of fuses to check in this vehicle to start with. If the Battery cover is missing, that's an issue. Sometimes it's not put back or forgotten about after a repair. Check for that as well.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

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