mikeqs

Not sure what's going on with my car. After some hard-ish driving (Around 1hr-1hr15min), the car starts to lose power and it seems to have trouble shifting and accelerating. It struggles to get over 80mph. It also won't downshift past 6th or 7th gear if I am going over 60mph. Acceleration is slow, as in dangerously slow. It takes a long time to get up to highway speeds.

I did get caught in a little bit of rain today, but I would be surprised if that damaged anything. The problem seemed to resolve itself after I parked it for a few hours. But the problem started happening again on my ride home. Any ideas? Is this something that I can fix on my own? Will it resolve itself overnight maybe? I really don't want to have to bring it in to the dealership. The last time something happened to my other car, it took a month to get a service appointment.

BLAM

Sorry to hear your trouble. Sounds like the vehicle has been abused, redlining and donuts.

superswiss

First thing to do in cases like this is to hook up an OBDII scanner and see if there are any error codes logged and then take it from there. It's anyone's guess as to what's wrong w/o some diagnostics. Also, define hard-ish driving. In addition what's the engine oil and transmission temperature when this happens? These cars have plenty of performance information displays to view health data. A good indication of whether you are in some kind of limp mode is to bring up the HP/torque performance display. If the scale for horsepower and torque is reduced to something way below than its rated power/torque then it's in limp mode and protecting itself. I know you said it won't downshift on its own, but have you used the manual mode? Does it let you downshift to a lower gear?

mikeqs

@superswiss thanks for the useful response


would this work?

FOXWELL NT510Elite fit for Mercedes Benz Diagnostic Tool,2023 Newest Full System fit for Mercedes Scanner Bidirectional Scan Tool,OBD2 Scanner Car Code Reader ABS Bleed SAS Oil Light Reset CKP Relearn https://a.co/d/dUgxN6O

superswiss

That probably works, but there are phone apps that use a dongle and are cheaper. Plus it's easy to keep in your car in case you need to scan on the go. For example Carly is a good app.

https://www.mycarly.com/

mikeqs

thanks, i think i’m going to go with the bluedriver which seems to have high reviews on both amazon and the appstore!

mikeqs

@superswiss to answer your question about how hard i’ve been driving. i was “cruising” between 96-103 for a bit on a long stretch of highway without many other cars around

engine, oil, transmission temp didn’t seem out of ordinary, but did not take notes.

superswiss

Oh, a Sunday afternoon drive . Yeah that's not really hard driving for an AMG, so must be some kind of a malfunction. You probably will have to take it in and get it sorted. These are complex machines plus first model year troubles.

mikeqs

plugged the obd tool in this morning, no error codes. will take it out for a spin if it doesn’t rain. otherwise will have to wait until tomorrow

klingsor

From my experience with so many vague engine issues in MB vehicles, if there are no current & stored codes the dealership will almost certainly hold the car for a couple days and return it to you without fixing anything. They'll tell you get back to us when it happens again.

My advice to you don't go to the dealership unless you're armed with photos of cluster messages and diagnostic codes you obtained from your ODB scanner. So have the OBD scanner in the car at all times, and when the problem shows its ugly head hook it up and pull the codes immediately. Then and only then take it to the dealer. Also keep in mind that if you get a CEL (check engine light), if it is flashing you need to stop the car as soon as possible at the nearest safe spot and take it immediately to the dealership. Don't drive it. If it's a constant CEL, you can drive the car to the dealership but don't push it too hard as the engine is not well and pushing it may cause the issue to develop into a major failure.

One time I was driving at around 30mph and the car felt sluggish. A couple seconds later a flashing CEL came on. I stopped on the shoulder and turned off the car. A couple minutes later, turned it back on and the CEL was gone and the car drove and shifted normally. Took it to the dealership and they scanned it for codes, and you guessed it: there was nothing stored. A few weeks later, the problem came back. I took it to an indy who found out one of the coils was failing. I changed all the coils & spark plugs and the problem never returned.

So in your case, the problem is likely to come back again. Just have the reader handy. If you don't get a flashing CEL, keep the car running and scan it for codes. Once you get the codes and photos of any messages on the cluster, take it to the dealer so they know where to look and they feel less compelled to dismiss the issue. Also remember that turning the engine off then on will in many cases resolve the issue temporarily until it comes back again which almost certainly will.