Are the ambient conditions the same?
FI cars will loose a lot of power in the summer months due to the IATs getting high and timing being pulled
You best bet is to log the car with a generic OBD2 scanner and see what the boost and IATs values are rather than depending on the butt dyno.

I don't think iat on these cars is available from any of the app scanners.
I've tried....

I had this issue myself with it feeling weak. My car was at the dealer for 16 days (sirius radio was cutting out so they replaced the wiring harness, they replaced the rear bumper because it was installed over a clip that was pushing it out, they replaced rear pads and rotors because of horrible squealing at all speeds).

When I finally got the car back stuff must've been reset because my garage door opener was no longer working. My car does feel much better off the line and throttle response compared to before. Not sure all of what they did but I think it has helped some.

I will be posting my work order here. This basically fixed it. This is caused by low battery in the car and it basically goes into a limp mode. So you have to reset all the systems in the car separately and then it goes away. Have seen several people with the same problem. I think this a very simple fix for all of you guys.

same thing happened to me, I was sitting in my garage trying to figure out the command, for an hour & watch a movie for another hour. Then when I got on the highway giver it 20% throttle comfort mode, it doesn't push me back into my seat like before. The first few days when I pick her up, 20-30% throttle in comfort mode on the highway @65mph would push me back into the seat. Feels like its much weaker. I brought her in and told my service advisor about it and he said a drain battery shouldn't have anything to do with power loss. So idk what to do know

Seems like a Star C4 system will be a good investment for DIY. You can access all the modules etc to see if any soft codes are stored and clear them.

I have had this exact same thing happen to me and the ONLY way to fix it is to have either MB or a certified MB mechanic reset all the computer systems. It CANNOT be done by disconnecting the battery or resetting something through the ODBII.
It was the most frustrating experience I have had with any car. But luckily I have a great local MB mechanic so I do not have to deal with the dealership. This issue really sucks but is an easy fix when dealing with a competent mechanic.

My suggestion is to speak to someone else at your dealership, try another dealership or try to find an authorized MB mechanic that works on the new AMG's. If you are in Los Angeles message me and I will give you a number to call

Unfortunately i'm all the way in Cincinnati Ohio. I'll try to show my service advisor this & ask him to do a reset on all the system. Finger cross, hopefully this will work for me and everyone else having the same problem

Has anyone try change out the batteries?

Ok here is the verdict at least for me. After months of dealing with this and trying different things I finally went to a local merc mechanic thanks to Mazyo! When they hooked it up to the system ( I presume Xentry ) they found miscommunication between the ECU/ME causing lowered performance. At that time I asked them why didn't the dealer tell me this when I took it in and they just shrugged and said it is possible they didn't want to do anything with it or didn't really look.

So to shorten the story, after they "reprogrammed" the ECU/ME, all my power is back. He said he has seen many 63s with this same issue due to low voltage tripping the "limp" mode and said once that fault code is registered, it has to be removed/reprogrammed to have it reset.

At the time ( earlier in this thread ) I thought to myself low voltage couldn't be an issue with my car but then it hit me. I have two Cellink B batteries that powers my dashcams and it charges when the car is ON. So I am guessing a couple of times when I went to get carwash, they must of left the ACC ON and that will trigger the charge and thus drained part of my battery enough to trigger a low voltage fault.

So my recommendation to you if you have this similar issue is take it to several mechanics if one says nothing is wrong ( like they did to me at the dealer ). My second recommendation is if you have many accessories like hardwired radars and dashcams even if they're only ACC HOT, invest in a deep cycle battery. I would recommend the Optima Yellow Top but they don't make ones that fit our cars last time I checked so perhaps the Duralast Platinum AGM battery would be the next best one which does fit our cars.

In closing mystery solved! At least for me.

amg8 do know the lowest voltage it goes down to before it triggers the limp mode

Unfortunately I don't however I am not sure how useful that information would be because the battery does not stay at that level once it gets charged back up so when you go to test it, it will show in normal operating range.

Since knowing about this and the solution, I am keen to find out how we could do this ourselves. I am not about to purchase any Xentry C3/C4 but was looking into Autel Maxisys Pro which has ECU/ECM programming capability. But too scare to jack things up unless someone which has experience can confirm it works.

I brought mine to the dealer asking if they can reboot everything & they hook up the batteries and said its all fine. I tried kick down in sport + at 65mph and torque and hp on engine data screen never show 500hp/500tq.. Ughh this is such a head ache. I'm also getting an ecu tune from renntech soon, hoping that can fix all the problems. I'm going to purchase xentry c4 and do it myself if I can't find a dealer to fix this problem. Will update everyone if I can reboot everything myself with xentry

I took mine to Mercedes today. The code PO61A62 shows up. This is what it says: The torque control of the control unit has a malfunction. The signal comparison is faulty. They tried clearing the code, but every time they started the car, it would come back. So they say I need to purchase a new ECU, due to modification to the control unit, because I had It tuned. So anyone thinking of getting a tune/ flash, might want to get this checked first.

Wow. How much is this costing you? I have P061A come up as well, but not everytime they start the car. Did they even try flashing you back to stock? That might solve this problem.

I will ask them if they tried that. If they did not I will ask them to, thanks. Ecu cost is $2500 cdn installed.

And did the dealership already void your warranty? Please do let us know what happens here. This is priceless information. Might really help a lot of people.

Seconded, don't leave us hanging!

To show you guys what this fault code PO61A62 does, here's a picture of my dyno graph.... And, to answer the question about warranty.... if anything can be attributed to the ECU, or any other modifications, your warranty will be void. I have had all my other cars tuned and modified in one shape or another without any issues. This is my first AMG, what I have learned so far, is that they do not like modifications to their cars. Which to me, is an oxymoron, because AMG started off in 1967 modifying Mercedes engines and cars.

I took mine out for a drive last night. In comfort mode if I floor half way it'll show 516tq on the screen & when I floor it past kickdown the power stay consistent & doesnt drop to 380. Sport + & race mode drop hp and tq to 386 at around 5k rpm. Took her to the dealer show them this forum. They said they'll hook it up for software update or reboot. Omg this is such a headache... for a 500hp car it doesn't feel like it. My cousin stock audi s4 feels stronger. Can anyone message me their service advisor number 🙏🏻 I'm going to send mine over if my dealer can't fix the problem as there's only few dealers in my area.

I agree, whole heartedly. I had 5 , 6 and 700 hp cars. From day one this car did not feel like a 500 hp car. That's why I went the tune route. which is a double edge sword,

I have recently used my car only week-ends. Last week-end I had a 1000km trip, and the next week-end I decided to connect the battery to CTEK MXS 5.0 text@charge device.
I tested the battery, and got "4", which according to CTEK-manual indicates "weak battery".

I was surprised - I thought that 1000km trip few days earlier would have sufficed to fully charge the battery.
I tested the alternator with CTEK, and it gave result "normal".

I do not have any extra power-consuming devices in the car.

According to MB documents, the car's logic is to keep the battery at around 80-85% charged. Any more than this, and it doesn't have reserve to reclaim the energy generated in coasting and recovery situations. It uses that 'free' energy to power stuff rather than using the alternator, reducing drag on the engine and therefore fuel consumption.

So I had mine checked by a local MB mechanic because I also felt the car feels slow compared to when I got it. There were a few codes related to radar sensors and electronic diff malfunction which he cleared.

I guess that means there isn’t anything wrong with the car and the next logical step is to tune.

Hey guys!

Read about this issue and had a customer come in the other day for a baseline dyno. Check out the video below to see how that went... 276hp on dynojet says it all.