FlyingBear

2019 AMG GT C Roadster, 2,600 miles, thankfully still under warranty.

I was driving on the freeway at 60-65mph (seriously, it's very busy today) for about 25 minutes. The check engine yellow symbol lit up but with no other messages or obvious issues. As the road is being worked on, there are no shoulders, so I continued, to the next exit a few miles ahead. After a couple of minutes, I saw that the turbo boost gauge was pinned to Max, even with very light throttle. I got off the freeway and shut the car down and locked it for ten minutes to see if it would reset.

On restart, the check engine symbol was still on, but throttle response and the turbo boost gauge were normal, so I headed home, just 10 minutes way. Two minutes from home, the turbo boost gauge maxed out again at very light throttle opening. My OBD II reader reports code P1523, which may include the Throttle Actuation Control, but seems to point at multiple potential issues. A faulty TAC could be correlated with the max boost indication. The car is being flat bedded to my dealer this afternoon, but I'm wondering is anyone else has experienced this issue. I've only owned the car for a month, but its codes haven't been reset since new, so this is a new issue for it.

CaliBenzDriver

I hope your local dealership is able to pin point the cause of this problem.

You can really help them by narrowing down when this bug shows up:

• cold/hot engine
• fast/slow driving road
• short trip/long trip

Hopefully your issue will get worked on by an Ace tech sooner than later.

Good thing you already know about the shut-off+ lock reset.
Another personal favorite is "whole car Reboot" by disconnecting batteries. This effectively resets the SAM's.
🤞

FlyingBear

My dealer is very good, and called me when the car was dropped off by the tow truck. We discussed the conditions under which the problem arose. I have little doubt that they’ll fix the issue. Good to know that a battery disconnect reboot is an option; that can cause mayhem on some cars, e.g, McLaren, Porsche.

CaliBenzDriver

Awesome to know your local dealer is exceptional. Pls let us know what they managed to figure out.

Many other folks will be interested to learn.
Thank you,
🤞

FlyingBear

Will do. I’ll post when I have a resolution.

FlyingBear

I talked with my SA just now. Mercedes corporate have made this a PTSS case, ie Germany is suggesting diagnosis and repair steps. They’ve seen this on other cars: sometimes it’s turbo exhaust clamp issues, but not always. Nice to know that they and the dealer are on the case.

CaliBenzDriver

Your dealer really means business! They're trying to get this worked on with best outcome possible.

FlyingBear

I got my car back this evening. My dealership sent me a video taken by the tech working on the car, and he explained what he had done and what the problem could be. A Mercedes TSB led my dealer to clear the P1523 code, which, apparently, usually fixes the problem. It is caused by a transient glitch in one of the check valves on the turbo plumbing, sometimes from a carbon buildup. My dealer tech found no carbon. If the problem reoccurs, the next step is to replace one or more check valves.

I drove the car home in 25 miles of heavy evening traffic. All seemed well, until, not far from home: after a stop, I gave it some gas and the car accelerated normally to about 45mph. However, right after that, I noticed that the turbo boost gauge was maxing out on light throttle. I'm new to the car, so I don't know if it's normal for the ECM to keep the turbos spun up after some heavy(ish) acceleration. As I slowed down for my driveway, the turbo gauge rose to about 80% of max on each downshift. If this is normal behavior, all is good. But, if not, then it's back to the dealer I go.

CaliBenzDriver

It started really well with your dealer being seriously commited to "The Best or Nothing".
The way your issue is already escalated to a German support engineer is very promising.

See if the problem resets itself for a while with a simple Ignition cycle (On/Off/On)
-Or if it continues until the car gets reset by the dealership.

If you have your own code scanner... indulge into scans for a glance at what's going on...
Intermittent glitches are never easy to pin point.
🤞

FlyingBear

Thank you for your help and advice. My OBD scanner shows a pending P1523 code, without the check engine symbol lit. All codes were cleared by my dealer before releasing the car to me. I guess that means that the glitch is still there but hasn’t happened enough to trigger an alert. An hour in heavy traffic on am 87 degree day got the underhood environment good and hot, for sure.

CaliBenzDriver

You're entirely right: the code is pending until the ECU goes through couple more tests and driving cycles.
Already the righting is on the wall, you know it, we know it but don't necessarily let the dealer know that or they'll start pointing fingers at you instead of fixing your automobile.

The root cause of P1523 was not immediately clear to the brilliant support engineers. In the end they will work out this factory defect given some time.

FlyingBear

The next step, per Germany, is to test and replace faulty check valves. Ideally, I can identify a situation that produces the weird boost gauge readings versus having to drive for an hour in the hope that it turns up. This evening it happened after a moderately brisk launch from a stop with a fully warmed engine. I’ll try that again tomorrow.

CaliBenzDriver

By the time they're done replacing the valves and the code keeps popping... they'll get to the pressure sensor circuits that drive the ECU that control these valves. After that it'll be software updates...

Helping them to reproduce the conditions will shorten the race to a solution.

FlyingBear

I drove the car to my dealer today and, of course, it performed perfectly. It performed perfectly when I went for a drive with the service manager, too.

However, after hooking the car up to the Xentry system, it verified the P1523 stored code, with an explanation that an evap system flap was stuck open. The dealer is ordering parts for various check valves to replace them.

I have nothing but positive things to say about the dealer. While I bought my E63S from them, the AMG GT C was a private purchase. The service manager spent an hour with me, at a shop that's crammed to capacity with other customers. He's committed to fix the issue, come what may, and I appreciate that. I've had similar positive interactions with other dealerships in the same (Hendrick) group and no negative interactions with multiple cars over the past 11 years.

FlyingBear

In case anyone is interested in the outcome: I got my car back today and there was no sign of the prior issues on my 25 mile drive home.

The P152300 stored code was diagnosed as a "check valve of evap system at partial load is jammed". The cure was to replace both purge lines. To be fair, they can't be 100% sure that this was the fix and will take the car back in again if the issue reoccurs.

Mercedes of Durham is now neck-and-neck with Porsche Southpoint next door to them for best service I've received. They're owned by the same guy and it shows in their service culture.

CaliBenzDriver

Thank you for updating your forum thread.

It's all good news... the EVAP problem is getting better and the excellent dealer seems committed to top grade service.

The underlaying emission system normally has an extended warranty coverage up to 10Yrs I believe. It works to recycle unburned green house fumes from gasoline.