Andrew Nelson

I'm brand new here so please forgive me if I make any errors with my post. I have a serious problem and am in desperate need of help for this situation. My 2014 GL450, with 75k miles, is going crazy with error codes when it gets wet from rain or car wash. It literally throws hundreds of codes when this happens. It is very difficult to get the vehicle in park because the constant errors popping up on the screen. It took over 10 minutes to get it to turn off because it wouldn't recognize that it was in park as it flashed many errors. I've already paid over $400 for the main battery replacement (engine). That didn't fix the issue. The vehicle has been at a very reputable Mercedes dealer in my area for the past week. They have put many hours into it, and were able to reproduce the problem by getting the vehicle wet, but they have been unable to find water or narrow down the problem in any way. Thankfully I have a brand new loaner vehicle at no cost, but for 4 hours of labor ($700) they've found nothing. They said they know to check the drains, and they've stripped the vehicle down. Sunroofs are common sources of leaks, but they see no problem. They have more than 4 hours in it for sure. But it seems I may be getting it back not fixed. This all happened within a couple weeks, where I did a lot of driving (hundreds of miles) and in all cases the issue happened within a few minutes of the GL getting wet.

At this point, if I get it back without being fixed I plan to try to wet parts of the vehicle until I can hopefully isolate a general source of entry (rear, back, top), but I fear that may not turn out to be as easy as it sounds. Dealership said that they would welcome any suggestions should I come up with anything from online research such as this. Thanks in advance!

mtm

Don't know if they checked it already, but look at the spare tire area in the back to see if it collects water. I remember someone having a problem there because of a leaky seal at the tailgate or taillights.

Just FYI, the main battery is not in the engine compartment, but under the second row seat.

nynd

Other areas to check are see if it ever had a new windshield installed. If they are not sealed right, you can have water enter the lower sides where the fuse boxes are. If you also see what the errors are, this may be a hint as to where potentially some may be located together.

chassis

@Andrew Nelson Time to do some digging in the vehicle. What is the history of this vehicle? How long have you owned it? How many miles are on it now, and how many miles did you put on? What service work or repairs have been done in the past year? What region of the world are you located? Please fill out your profile, as this helps others to help you.

Possible causes:
- moonroof/panorama roof
- windshield
- door seals
- tailgate
- taillamps
- fording water (driving through puddles or crossing streams)

Betty_Benz

[QUOTE=Andrew Nelson;8147495]2014 GL450, with 75k miles, is going crazy with error codes when it gets wet from rain or car wash. It literally throws hundreds of codes when this happens. It is very difficult to get the vehicle in park/QUOTE]

Start with front and rear SAMs (front first). You probably had/have moisture building up and wetting the main electrical brain.

Remove both front seats (make sure you leave plugs under seats connected so you can push seats fwd/bckwd to get at track bolts). Push pass. seat all the way up & fwd and disconnect dr/pass under seat plugs. Then remove batteries (don't forget tiny memory battery) under pass. seat Now you should plainly see water buildup or residue (water line) from it. Pull the rubber drainplug if there is any. Pull back dr floor and carpet & check for water damage to stereo electronics. If ANY water over a 1/2 inch, your Amp is probably fried.

Disconnect connectors from front SAM (black plastic box next to battery) and remobe the 10mm nuts holding it in place.

Rear SAM is located in the back passenger floorboard, in corner, below headlight. It can be accessed by pulling spare tire and spare tire felt trim.

SAMs- Plastic clips around its peremiter allow access so you can inspect the main board for corrosion. You can attempt to use a wire brush and some baking soda/water solution to GENTLY remove green or white corrosion that is shorting out components. If ANY components fall off when scrubbing, or if any of the solder runs have been eaten through, the SAM should be replaced.

Reinstall in reverse order, clear codes and perform system checks. Then go on the hunt for your leak.