Checked power, grounds, and what signals I could last night, as well as associated wiring, all looks good. Trying to scare up a wiring schematic for it all so I can really wring out the wiring, but schematics seem as easy to find as hen's teeth.

I'd guess a low-DEF condition would supersede a non step down emission failure.

I don't really have a problem with the low DEF step down and the 10 start issue when its related to low or no DEF on-board. When I bought my cars I understood the requirements for DEF and its really not any harder than adding windshield washer fluid.

However the 10 start solution when faced with a bad NoX sensor (if actually true) seems a bit arbitrary and absurd. On any gas powered vehicle a malfunctioning O2 sensor will trip a check engine light but the car will continue to operate. Why does the EPA apparently consider it necessary to give the Diesel 10 starts and then shutdown the car? Seems a little biased against the Diesel? If emission system malfunctions require shutting down the Diesel powered vehicle shouldn't we require shutdowns for similar gas powered malfunctions?

Next time I have one of my bluetecs on the lift I'm going to unplug both NoX sensors and go for a drive. I'm still not convinced Graham's 3rd hand account of what he read on the internet is correct. I'll update this thread when I've done my experiment.

I agree, can't help you with the wiring diagram. You'd need online access to Star diagnostic system at the least.

It's nice to know that there is an option to replace just the heater - I'll be following to see how the repair turns out!

The wiring diagram should be in WIS. If you don't have access, send me a PM with your VIN and I will see if I can find one.

If you want to improve that to 2nd hand, go read the 10 start posts on MB-World yourself.

Most reported a CEL light coming on, then a little later, the 10-start message. Problem was too tight specs for NOx removal to meet Euro standards. Corrected by a software change and often new NOX sensors (some were faulty). Nothing to do with Adblue supply.

I had all this confirmed by my dealer once they learned what was going on. They updated my car before anything went wrong. Others on MBWorld were less fortunate and had their car's sit at dealers, sometimes for months before problem was corrected.

BTW, my pristine 2014 GLK250 with just 31k miles is still sitting on dealer lot 10 months after I traded it. It doesn't have all the bells & whistles people seem to want, so that may be a factor along with anti-diesel sentiment.

If our GLK had had a CDI diesel, I would still have it!

My GLK250 has 80k miles and has never had any issues with the adblue system. Last december it prompted me to refill the system so I bought about 6 gallons at the dealer (about $23), poured it all in, and that was that. No messages since....hasn't needed any added either....its been several thousand miles.

Why trade in at 31k miles? Bad experience with the car? You still had warranty at that point correct?

Mine is minimally optioned....main more unique items I have are the panoramic roof, black ash wood dash, power rear hatch and running boards.... I have no navigation, no blind spot mirrors, no backup cam, no lane assist/park assist/stop assist, no HID lights or any of that stuff.

Car was 5 years old and used mainly when we traveled South for winter. We had no engine problems, but the transmission was changed because of a problem with the torque converter.

Original warranty was for 4 years, so had expired. I had bought the extended warranty that added 2 years plus one on power train. Sounds good, but the Canadian extended warranty is not honored in the USA. You have to pay dealer for repairs and then submit claim to Mercedes Canada.

When you read the fine print of the extended warranty, you find that many emission related items are not covered. Many owners were experiencing problems with particulate filters, Nox and other sensors and the Adblue feed system. Some of these cost in the $1000-$3000+ range to repair at dealer and sometimes car is stuck at dealer while awaiting parts or MB problem solving help. No free rental car for such repairs! Not something we wanted to experience while away from home with just one vehicle.

We now have 2019 Subaru Outback. Bigger, equal or better fuel costs, lower cost initially, lower dealer service costs and less depreciation. We will likely trade it after 4 or 5 years. It isn't a Mercedes, but it is a very nice vehicle. Happy to no longer have that high maintenance chemical plant built in to clean up the emissions :)

But don't get me wrong - I loved to drive the GLK

I got lucky and had the DPF replaced under federal emissions warranty right before it hit 80k miles....check engine light came on for it at about 78,300. No issues with AdBlue system at all....even in the arctic cold winter.

As for a subaru being a more economical alternative....only if you trade after 5 years like you said. CVT in that car costs about 8k to replace....and will fail eventually....as may the engine. I know someone who had the 2.5 engine in his forester fail at about 80k miles....he got lucky and had the expensive extended warranty he had paid for when he bought the car.

Do yourself a favor and just delete all that crap off your 642. The first problem I have with my ML I will be removing all that EPA crap.

That's the plan. I told the Mrs. that this is the one chance it gets. Next DEF/DPF issue that comes up, I will be pulling the ECU, and getting the tune to disable the EGR, Swirl flap motors, and entire AdBlue system. I have found a few places that do it but have not heard from anyone that has had it done yet.

Do you have a way to reprogram the computer ?

There are a few over in MBWorld Diesel and GLK forums. But all in Canada, I think.

Yep

Can anyone tell me, or direct me to where I can find some info.......I got the replacement DEF pump today (still waiting on the heater) and the pump came with a syringe that has a wide opening at the end but no written instructions. Now replacing the pump is pretty straightforward, three bolts, a hose, and electrical connections, but what is the syringe for? Does the pump need to be filled or primed before installation? Have not found anything saying it does, but again, why the syringe. Don't want to burn up a new pump if it needs to be filled, but don't want to wreck it if it doesn't. Help greatly appreciated.

I read over the documents about the AdBlue system on the W166 and it looks like the syringe is just a provided tool to empty out the AdBlue tank prior to service work. I found nothing about needing to prime the pump.