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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 29068
Experience:  Over 15 years experience as a Mercedes dealer technician
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Mercedes Benz GL450: I have a 2009 GL450 that had the wipers

Customer Question

I have a 2009 GL450 that had the wipers decide to go out on my wife when she was driving on the Turnpike while raining. We haven't had this issue before and we've owned the vehicle for about 6 months now. After searching online fast about the hood needing to be closed for wipers to work I then had at least a starting point.
When I got to the vehicle the wipers worked only about 10% of the time when I turned the car on/off and hit the stalk. I looked at the hood closed switch and saw a small piece of debris where the contact was so I lodged that out and it seemed after shutting the hood, the wipers turned back on and worked the rest of the day, I thought all was well.
Today I got another call from the wife when taking the kids to school, the wipers stopped working on the way back home (while raining). So apparently the debris wasn't the root cause for what is going on.
I don't have any diagnostic tool, if I purchased one, would that go deep enough to tell me if there is a sensor not being made? My only thing to go off right now is the hood switch is going bad? I thought I read somewhere though that over 5mph, the wipers should work regardless of that switch being made (for obvious safety reasons). I also read something about the drivers door switch but would that be the same assumption with speed and overridding it? If so, something else is causing the wipers to stop while the vehicle is driving down the road at 70mph.
Submitted: 1 year ago.
Category: Mercedes
Expert:  Pete replied 1 year ago.
Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay. I dont suspect this is the door switch at fault as they should still operate but if the hood switch is at fault it can cause this here.On some models you would see a warning in the dash if the hood switch is not activated like a message "hood open".What can cause this here is a fault with the wiper switch itself or a fault with one of the SAM control unit/ECU's as these can fail needing replaced.Unfortunately the type of scan tool you would need would be one that can be expensive as the cheaper ones are unable to read all computers and you need one you can plug in to read all computers to see what codes are set needing diagnosed and repaired.This does need done to check for any codes in any SAM control unit as well as observe the data signals from the hood switch and wiper switch for any issues.Once this is checked the fault is located and can be repaired from there to correct it. If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.Thanks Pete
Customer: replied 1 year ago.
The dash has not shown the hood open error message, if it thought it was open and it was causing the wipers to stop, would that also trigger on the dash? The same with the door, we don't get those sensors going off so that may not be the cause. We did get a check coolant level the same day so I'm hoping it isn't a fauly SAM module, do the coolant sensor and wiper motors just through the same SAM module?
Expert:  Pete replied 1 year ago.
The coolant sensor sends a signal to the engine computer.I have seen faulty engine coolant temp sensors needing replaced as well as slightly low coolant causing this fault here.As for the wiper issue with no door open or hood open messages you may have a fault with a SAM control unit needing replaced.I have ran into this before.This unfortunately would have to be tested further to locate for sure if this is the cause here and then replaced and programmed by a Mercedes dealer or authorized Mercedes repair center. Let me know if you need anything else and feel free to rate my help here. Thanks Pete