First time I have had to post in here for an issue with my car so bear with me as I try to explain, haha. I have a 2014 Mercedes GL 450

Tuesday morning, I was driving my son to school and about halfway to his school I had a few random lights/messages come up on the dash: "PRE-SAFE Functions Limited See Operator's Manual", "Parking Brake See Operator's Manual", "Blind Spot Assist Inoperative", "SRS Malfunction Service Required". These came on intermittently through the last half of my commute. After I dropped him off, I parked, turned the car off and back on, and started on my way home. About halfway through my drive back home those lights started up again, same ones, intermittently.

That afternoon, I left to go pick him up, and no issues at all until after I was 2/3rds of the way to his school and those same lights came back up intermittently. I picked him up, headed to get my daughter from her daycare, and as we left her daycare and headed to the baseball field I got more lights/messages: "Inoperative See Owners Manual", "Adaptive Highbeam Assist Currently Unavailable See Operator's Manual", "Lake Keeping Assist Currently Unavailable See Operator's Manual", "Service Required Do Not Shift Gears Visit Dealer", "Cruise Control Inoperative".

I got to the ballfield and parked and once we finished up there to head home, I started the car up again and all those lights came back on. I was able to drive and mechanically the car feels fine, but I had no speedometer, no blinkers, and the car wouldnt accelerate beyond about 4th gear. I pulled over about halfway home to see if I just needed to turn it off and restart it. It wouldn't go into park. So I just had to turn it off. I turned it off and went to restart it and it wouldn't crank. All the interior lights came on, but the engine wouldn't crank. I then waited about 5 minutes and then turned it on again and it turned right on, but still had all the lights on the dash. It would not go into reverse. It was stuck in park. I turned it off and waited another 5 minutes. I turned it back on and was then able to move into reverse and got myself and the kids home safely.

Wednesday morning I decided if I turned the car on and the lights were off, I would take the kids to school. My husband has been out of town for work all week and has our other car. Got the kids ready, went out to the car and it started right up with no lights so we ventured on our way. Got my daughter to daycare just fine and after we left her daycare all the lights started coming up again. Got my son to school and made it home.

I booked a mobile mechanic to come out Thursday as that was the soonest available. After I had been home working all day Wednesday I left to go get my kids from school. Went to get my son first and all the lights came back on on my drive to get him and when I got to the school the car wouldn’t go into park so I had to turn it off and then turn the key one click and then it was able to go into park. I went in to get my son, came back out, and couldn’t get the car to start. All the electrical components came on, all the dash lights, air conditioner, but the battery wouldn’t crank. Turned it off and waited 10 mins and tried again. Same thing. Waited another 10 mins and tried again, same thing. At this point I went into the school to ask if they had any jumper cables and one staff member did. After some time we were able to get my car jumped off and get it into drive so I could make it home. Parked the car and didn’t touch it again til the mechanic came Thursday.

Mechanic came Thursday and did a diagnostic check on my car and the alternator is fine but both batteries were dead. He replaced those and ran additional diagnostics 3-4x before he left and all of the lights on the dash showed as being fixed. Everything looked great when he left. No lights, no errors; new batteries working perfectly. Drove it Friday morning to drop both kids at school and it felt like driving a brand new car, it was great. Fast forward to the afternoon, I picked my daughter up from daycare and then my son from school. On our way home from his school all of those lights in my below post started showing up again.

What on EARTH could be wrong with this car? Of course this happens while my husband is out of town for work and has our second vehicle. Any thoughts on what this could be? From everything I have googled it seems that it could be a SAM issue or an F32 fuse. Could the alternator be going bad even though the numbers are in the right range? Any other ideas?

 

You're having an issue with one of the car's CAN networks. Those are communication systems that run throughout the car. It could be water intrusion or a component that is shorting one of the networks. You'll need to bring it to a dealership or a competent independent repair shop who specializes in Mercedes-Benz and has the proper diagnostic equipment.

 

Is there anything my husband can check at home? He’s a mechanical engineer and very competent with German cars. If not, do you know how much something like this would cost to inspect, diagnose and fix at the MB dealer? I ask because I just sunk $650 on two batteries and labor to have those replaced and really don’t want to spend an arm and a leg on something else.

 

This needs a proper diagnosis, take it to a competent mercedes dealer-service center

also include your husband on the decision making if he's not already involved. If he's as competent as you say then he's familiar with star/xentry diagnostics and can sort through any codes and track it back to modules or harnesses that may be affected. Also there could be a bad ground somewhere from overspray of paint, corrosion, water intrusion, rodent intrusion and damage. If he's the real deal he can identify all this - and will he have the time to do all this? Or is it better to pay someone who will absolutely get to the bottom of it and you'll have your time freed up?

Totally get it, no one wants to spend any money on anything unnecessary but if it's broken you need to get it fixed or replace the vehicle. If the car costs a lot to fix, more than you want, you'll decide what to do then

 

I would suggest checking all battery connections for a loose ground. Happened to mine after having a battery tender pigtail installed. Turned out that they didn't tighten the ground cable.

 

Agree on the water intrusion comments. Also it could be time for a new battery, and new auxiliary battery.

Check the rear spare tire area for signs of water. MB SUVs are known for leaking through taillamps and around the liftgate area. Also check the sliding roof drains are not plugged.

 

All your husband can do without a dealer level diagnostic computer (XENTRY) is to pull up the carpets (not particularly easy) and look for water in the floor pan. Otherwise this could be as simple as a bad parking/radar sensor, or it's connector behind either bumper with moisture intrusion causing a shorted CAN network., or one of a hundred other things.