blockage

Howdy Gents and Ladies... I need some help with some ideas as to what this problem is.

105k miles 2018 GLC 4-matic. When driving from Phoenix up to Vegas, I had the cruise on at 82.
We start going up one of the many hills on that drive, and she started losing power, never downshifted, and then popped out of cruise.

For the remainder of the 4 hour drive, every time we had a hill to climb, I had to manually downshift to get any kind of power.
But even when downshifting, where I'd have 3-4k rpm, I wouldn't get the power to the wheels. I was dropping from 80mph to 65 mph. It seemed to stabilize in 5th gear.

No noise from engine or transmission, and no indicators on the dash. I don't have my scan tool, so I haven't checked for any codes that have been thrown.

My first thought is that the transmission is slipping and not getting power where it needs to go. Note that I have NOT had the transmission fluid/filter ever replaced...it was on my to-do list once the weather cooled down :/
Does this description sound like a transmission issue? I'd love to hear any thoughts of ways to troubleshoot before I bring it to a shop.

We are on a road trip up to Montana, but I have a few days in Vegas...so I may be able to get it into a shop. Or I may just rent a car to do the trip... waiting to hear what thought y'all might have.

Thanks for any assistance!
---John

Plutoe

sounds like is dangerous----you need a scan regardless of the lack of no check engine light

Iceclimber7

Agree with getting it scanned/looked at but I might also look at the fuel filter - also were you heavily loaded and was it really hot out ? If you were going into limp mode I'd expect some warning lights for sure.

mikapen

Fuel filter is worth checking.
An easier check is to remove the gas cap and see if there's a big suction released. Poor venting gas caps can cause loss of power.

blockage

Thanks for the replies so far...
From a bit of research elsewhere, others have mentioned that an issue with the turbo could also result in a loss of power when climbing a hill.
I'll definitely be getting it scanned to see if there any codes that didn't cause the check engine light to show.

Going to be renting a car in the meantime to do the rest of the trip and then get things taken care of on return...

Other thoughts are appreciated! I'll reply results when I have some. Thank you!

sn202020

You might want to check if the wastegate actuator is the reason for the weak power.

i had felt the strange weak engine power for a while before i actually saw the P0299 turbocharger underboost code.

https://mbworld.org/forums/glc-class...ml#post8991461




if you have a vacuum or a syringe with some tube, you can check vacuum is leaking or not. And see the rod is moving 13mm or more by vacuum.