Bad run of luck with my Bluetec
 

I've already had quite a few issues, major and minor, with my 2012 ML350 Bluetec. Unfortunately, things have continued.

I went in for my 50K miles Service A about a month ago, came home and parked the vehicle for about 10 days while out of the country.

Two days after returning I get a check engine light. Of all the problems I've had, I've never had a check engine light. I called the service advisor on a Friday and scheduled the ML to go in Monday for analysis.

Over the weekend, I notice some oil drips on my garage floor. I was hopeful this was just some dripage from the underbody panel --maybe the tech had been messy with the recent oil change.

Turns out, I had two significant issues:

1) The AdBlue/DEF heating circuit in the tank failed, causing the check engine light. A little research shows this has been a relatively common failure both in MB diesels, and for other manufacturer's DEF equipped diesels as well. MB owners have been quoted anywhere from $1100-3000 for repairs. That's really pricey, as the repair doesn't sound difficult: Remove right rear wheel, remove fender liner, drop tank, swap out heating unit from tank.

2) The oil leak was from the oil cooler. These failures have been reported in MB diesels going back quite a few years. The repair is a big deal. The covers and air filter housings came out, the inner firewall partitions were removed, including the wiper assemblies, then the turbo and both fuel rails, both intake manifolds, and the exhaust gas cooler, to finally get to the oil cooler. The transmission had to be separated from the engine bell housing to adequately clean everything up. The oil cooler seals were replaced (that's been the same mode of failure for years), and everything put back together.

On the up side, I've got the extended warranty so I didn't have to worry about fighting with MB over these two failures which would have cost thousands of dolllars to repair out of pocket, with my car only 200 miles out of warranty. I don't usually buy extended warranties, because most vehicles I've bought in the last 15 years have been so darned reliable, but because of all my earlier issues I made sure I had one for the ML.

To add insult to injury, after I got home from the dealer I tried to open the right rear door with the outside handle. New problem. The door didn't open-handle's broken.

I'm hopeful I'll have better luck in future, but the pattern has not been good to date. On the other hand, I've had lots of opportunities to test drive MB loaner cars!

At lease you got a MB loaner, I got taken to the local car rental and wa given a nasty Nissan Sentra!

Sorry about you problems. Glad I got the extended warranty, but hope I do not need it.

Yes, thanks for the support. Nice loaners make all the service stops somewhat less painful.

My dealer has done their best, but the number of issues has gotten tiresome. Certainly the worst reliability I've had in any vehicle for many years. I priced out a diesel Cayenne on line last night. About $10k more thanks to overpriced Porsche options, but if I can convince myself the reliability is halfway decent, that's probably the way I'll go next.

I really liked the Bluetec engine, but service history was terrible. Over the period of ownership, at least 20 CELs, oil cooler, adblue heater, command system, fuel tank sensor etc etc. At least 3 months in service. Luckily loaner car provided.

I'll chime in as well. Our 2012 ml bluetec has had these same issues in the course of 6 months. In 11 months of ownership, it has been in the shop for at least 1 full month.

Misc. Issues fixed under Warranty:
Oil cooler seals replaced
Front differential replacement
1 front Wheel bearing replaced
DEF Heater (just last week) at 48k miles
Headliner replaced
Drivers door hinges replaced
Drivers seat bottom replaced
Both front shocks replaced
3 oxygen sensor replaced
Stumbling/hesitation issue that has been mostly fixed, but still get the initial morning take off stumble for the first few seconds of driving...then all is fine.

Dealer has been very good and accommodating. Always has a new mercedes loaner avail.

If we didn't love the ML bluetec as much as we do it would be gone, but nothing out there temps us to sell.

Thankfully we have the CPO warranty and a great local dealer...which helps ease the pain.

Sounds like some of these problems are fairly widespread. I also really love the diesel (when it's working).

I've also had the DEF tank sensor issue, several visits for transmission problems, eventually resulting in a new transmission, and a whole host of smaller, annoying problems that required dealer visits. On one occasion the power lift gate failed one day after a transmission repair.

Sounds like some of these problems are fairly widespread. I also really love the diesel (when it's working).

I've also had the DEF tank sensor issue, several visits for transmission problems, eventually resulting in a new transmission, and a whole host of smaller, annoying problems that required dealer visits. On one occasion the power lift gate failed one day after getting the ML back from a transmission repair.

Quite a few of my problems were clearly related to build quality and quality control. Definitely a vehicle needing an extended warranty.

u should get a lemon attorney. i did and the matter my situation is settled.

Why would any of these repairs have cost you anything on a 2012 ML? Do you not have a full four year warranty?

We had an extended warranty to 100,000, but after that still incurring expensive repairs so traded for a gas '14.

Did you get the 3 oxygen sensors replaced due to jerking/bucking? Are these sensors part of the exhaust system?

^ the sensors were part of the exhaust system, but didn't have any effect on the bucking issues. They were simply check engine lights that turned out to be faulty oxygen sensors.

What has been determined as the reason for the bucking issue? My dealer said that the diesel I bought messed with the sensors. They replaced the exhaust and the bucking was gone however every morning when I leave my house the car hesitates once when I drive of slowly.

^ dealer worked on our ml 3 different times to correct the bucking issue. The 3rd time they did a hard/manual reset of the transmission. After that, no bucking, but every morning after backing out of the driveway and taking off, it will do a quick hick up (only once and for a second). Then all us fine the rest of the day.
This past July MN changed all diesel to bio 5-20%. I was quite worried it would mess up the sensors and make the vehicle buck again, but all has been fine...except losing about 5 % fuel economy with the crappy bio blend.

They reprogrammed my transmission too but that didn't help in my case. I couldn't find anything about bucking issues caused by biodiesel, so I have a hard time believing that. But I've read that biodiesel can cause engine damage in the long run after 40K or 60K the fuel system may get clogged up

I have come to the conclusion that it is not worth owning these fabulously intricate vehicles, beyond the warranty period. The car companies are designing them to slip into planned obsolescence after 3 to 4 years and 50,000 miles or so. They figure that they will either get us on the lease or purchase or they will get us on the repairs & parts down the line. I guess so many of these cars end up in third world countries where mechanics come up with "bailing wire" techniques to keep them running, long after folks in the first world are done with them.