Hey MBWorld!!

I was working on my GLK350 4MATIC (2014) and after having the vehicle lifted (4 jack stands) in D to diagnose vibration taking place my GLK started having odd behavior in Eco mode only. When stopped, with or without the HOLD for braking or with the engine off from Auto Start/Stop, it is shifting between D1 and D2 repeatedly. This behavior isn't observed in S mode. Has this been seen by anyone? The car drives fine, and upshifts/downshifts fine at the correct speeds. This is only taking place when the car is stopped in D, in Eco.

Thanks!!

 

When were fluid and filter changed ? It only uses first gear in sport mode, what codes did the reader show ?

 

I haven't scanned it quite yet, ran out of time yesterday. As far as I know transmission fluid/filter hasn't been serviced yet (I got it at 106K and it's currently at 110K miles) which is overdue and this service item wasn't listed in the CarFax. I am suspicious if having the car off the ground in Drive may have confused the TCM? I haven't done a transmission reset yet as well.

Won't have the ability to scan for about ~2 weeks.

Yes, in Sport mode, no issues at all. Only takes place in Eco (which typically starts only in 2nd).

Appreciate any insight

 

I would change the fluid first and filter , the interval is about double what it should be anyway. Just like the bs 9000 mile motor oil and no differential oil change ! It’s all manufacturer bull s to make people think vehicles are cheaper these days . Change it !

 

Thank you, will do! Was already planning on doing this since it's overdue, and yeah, no interval for differential fluid is a big LOL.

Will follow up when that's been completed, or, if I can find the codes before then, if any.

 

@Mmr1 After troubleshooting a little more today, we found the root cause to be an LED trailer hitch cover with a 7 pin to 4 pin conversion. When removing the trailer hitch the transmissions operation in D has returned to normal.

Is there some advanced calculation that's done when there's a 'hitch' connected that would want the transmission to shift from 2nd to 1st over and over? Even if not compatible it's very odd that the hitch being powered would cause this sort of symptom.

Mostly putting this out there for anyone else out there that experiences this very weird quirk.

Thanks again!

 

A cover that’s lighted ! Nice , adding anything to Canbus is known to cause gremlins . A trailer hitch, so it towed, and fluid is original doesn’t sound healthy , good you found the issue !

 

The trailer hitch advice is very useful.
As for the why, it’s pure speculation, but even when in ECO, the transmission will shift to 1st gear if the accelerator goes rapidly to WOT at speeds below about 11 MPH. May be the hitch in the CANBUS circuit interfered with that logic.

 

Could it be based on "presumed" additional load? Depending on trailer size, and material from which it's built, even an empty trailer could add a nice bit of additional load/weight to accelerate and pull around. Plus another, at least, two tires adding some extra rolling resistance. Maybe the sensing of a trailer being connected (purely based on the "new" electrical connection) modifies shifting in ECO mode to include 1st gear even without rapid accelerator movement to WOT.

 

But isn’t the hitch aftermarket Chinese Light Cover on it? I’ve heard of cheap led upgrades doing crazy things with Canbus , Canbus glitches are normal with non Canbus stuff

 

I think the O.P. is referring to something like this:https://www.opt-7.com/products/7-way...e-tailgate-led




I noticed this caution NOTE for one of their similar products:




Only mentions lamp-out sensor but who knows...

 

If it's a factory towing setup (the wiring, not necessarily the hitch itself) then it senses a trailer based on whatever is plugged into the back. Based on that the ECM modifies shifting, among other things, to better handle the load. Throw in a 7-4 wire converter and some LEDs and all bets are off.

 

Exactly what I was thinking but did you find that info. in B&W somewhere?

 

No, it's just SOP these days. Often it's mentioned in the owner's manual.