Hello all,

need some help. Car went into soft limp mode and this time it’s not the exhaust flaps. I scanned the car with an Autel Ultra lite and found lots of module with errors. Many error codes are saying lost communication with module and lost communication with electric lock.

the car starts and runs great other than in soft limp and only allowing 354hp max.

any help will be much appreciated.

2019 C63
33k miles
stage 2 tune but removed for testing
battery/alternator checked out (still original battery)

@C63_boo Because you said it's the original battery I would check your battery voltage and connections in the trunk again. I saw that your post says they were "checked"... what does that mean? Did you put a volt meter on it? Did you load test the battery? Are both terminals tight? Was there any corrosion on the terminals? The battery should be at at least 12.6 volts with the car off, and you should be seeing about 14.1 to 14.7 volts with the engine running. While it may still be able to start your car, a low or dying battery will cause all kinds of module errors. After that, post some of the codes you are seeing and maybe that will point someone here toward what the problem is.

Wow, 89 DTCs. You may have some type of BUS issue. What are the majority of the codes reporting as? Have you recently been working on it and maybe left something unplugged? Make sure your battery is actually ok. Clear codes and rescan to see what are the ones that are hard faults.

Been so busy with work. I’ll try to post some codes later but many of them say loss communication or loss communication with lock ignition. Car runs and drives fine, like everything still works from lane and wheel assist to all cameras all. Just stuck in limp mode. I thought it was the exhaust flaps again. So I worked on that to get it unstuck. Nothing else was being worked on.

wonder if there’s a software update that I missed.

Here are a few codes. Pretty much all say almost the same.
Battery was checked by a technician and the scan says both battery and alternator are good.

Just bought a new main battery and coded it in and still having issues. Now the ESP module turned green. Will trouble shoot again tonight or tomorrow.

clear the codes and see what comes back

Ok, finally had time to trouble shoot. Turns out the new battery made all DTC go away except the esp and HUD. However, there is a humming noise coming out of a module located underneath the coolant reservoir. Not sure what that is? See video attached.

here are the last few DTC.

I think that is your intercooler fluid pump... Although yours sounds rough... Mine sounds like a smooth electric motor (high pitch tone like a drone's propeller motor without the fan blade) and it runs for a little bit after the car shuts off... But yours has some kind of buzzing sound to it.

Glad the new battery made the DTC's go away.

I don’t get it. I got all DTC to clear out now. Car been driven for the last few days and all green but still stuck in limp mode. Power allow is 353hp shown on the dash.

Does anyone have any idea? Software update from MB?

I do have an Autel MS Ultra Lite not sure if this tool can do any MB software update.

After many months and no one here can help. I finally figure out the issue.

I have a ZAC intake system and heat shield. The heat shield needed to use two or three sets of screws that has ground lug being attached to the engine. The spacers needs to fit between the heat shield and the screw and the ground lugs. Two of the screws came loose. After retighten and torque down, the loss communication went away and the car runs great again.

Hopefully this can help others who uses these ZAC intake system. Make sure those screws get retightened.

@C63_boo I also have the Zac Intake and those ground screws you speak of are supposed to be relocated to the adjacent hole. They shouldn't be sandwiched between the heat shield and spacers. See photo below from the installation instructions.

nice. I bought mines like 5 years ago and no instructions or very little. Next time when I’m in there, I’ll have to move them over like your photos.

I'm glad that everything is working again now,
however the cause sounds somewhat unusual to me.

You have in the US DAB Radio ?

yes, I believe so.

Forgot to mention that I took the car in as I thought it was software related. MB saw my 200cel downpipe and fouler plugs and quickly said that those were the issues why the car is in soft limo mode. They charged me $300 for nothing as they did not want to look at my car as it was modified.

my Launch x431 pro kept telling me that it has something to do with the front SAM or circuit 15. Spoke with ChatGPT and we nail it down to those lose ground studs. Lots of trouble shoot, looked through fuses, relay, replaced both batteries and all.

Hey im having something similar for reference, i have the zac intakes aswell. My car would shut off randomly under low load and all the lights would pop up and it restarts instantly. Could that have some to do with it. ive bought new aux battery, new battery and pretty much tried anything so any advice could help.

@slowestbenz did you see my picture about the proper grounding when using the Zac Intake?... Make sure the ground wire is moved as seen in the picture so the heat shield bolt isn't the only thing sandwiching it.