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2020 GLC300 4Matic. US model. ~78,889 miles. Purchased new from a Mercedes dealer. Sole owner.
Hey everyone — quick question.
My check engine light just came on out of nowhere. The car was running perfectly fine before this, and I just had routine maintenance done by my independent mechanic. Edit: a new MB battery was replaced. not sure if that matters.
Now the car won’t accelerate properly. It moves, but feels sluggish and kind of jerky, almost like the transmission is hunting or shifting back and forth. I’ve restarted it a couple of times with no change.
I also tried tightening the gas cap and switching between Sport, Eco, and Comfort modes, but nothing made a difference.
Any ideas what this could be?
(and also, do you think the mechanic could’ve messed around with the computer to cause this so I can come back and spend more money I hate to think that, but anything today is possible)
Last edited by 2020GLC4Matic; May 10, 2026 at 01:56 PM.
2020 GLC300 4Matic. US model. ~78,889 miles. Purchased new from a Mercedes dealer. Sole owner.
Hey everyone — quick question.
My check engine light just came on out of nowhere. The car was running perfectly fine before this, and I just had routine maintenance done by my independent mechanic.
Now the car won’t accelerate properly. It moves, but feels sluggish and kind of jerky, almost like the transmission is hunting or shifting back and forth. I’ve restarted it a couple of times with no change. You should bring the car right back to the mechanic since clearly they messed up something.
I also tried tightening the gas cap and switching between Sport, Eco, and Comfort modes, but nothing made a difference.
Any ideas what this could be?
(and also, do you think the mechanic could’ve messed around with the computer to cause this so I can come back and spend more money I hate to think that, but anything today is possible) https://cimg6.ibsrv.net/gimg/www.mbw...bd90174d0.jpeg
At least it is not flashing? If not flashing, you will need a scanner to see what it is it about since CEL can mean so many things. Especially that you are experiencing all those symptoms might not be a good idea to continue driving. Flashing means to not drive at all.
Last edited by W205C43PFL; May 10, 2026 at 01:30 PM.
At least it is not flashing? If not flashing, you will need a scanner to see what it is it about since CEL can mean so many things. Especially that you are experiencing all those symptoms might not be a good idea to continue driving. Flashing means to not drive at all.
thanks for the important aspect. I did bring the car back home and switched out to another. I’ll take it to the mechanic tomorrow. Thanks!
My independent mechanic ‘fuel rail pressure sensor’ that was the code, but he sent me back to Mercedes dealership. because he says there is an extended warranty and it has to do with fuel system and he says they’ll probably cover it so that’s where I’m at, but can anybody share more information on fuel rail, pressure sensor? I’m not a mechanic at all.
My independent mechanic ‘fuel rail pressure sensor’ that was the code, but he sent me back to Mercedes dealership. because he says there is an extended warranty and it has to do with fuel system and he says they’ll probably cover it so that’s where I’m at, but can anybody share more information on fuel rail, pressure sensor? I’m not a mechanic at all.
I find it rather interesting this happened right after your mechanic did work on the vehicle, are they just trying to evade responsibility?
Dealer repair/resolution: 78902 100 CONNECT BATTERY CHARGER , PERFORMED SDS TEST --CODE---> P019185 The rail pressure sensor has a malfunction. There is a signal above the permissible limit value , PERFORMED SOFTWARE UPDATE FOR M.E CONTROL UNIT AS PER FAULT CODE.
Is this something I could have done, a software update screws up my whole weekend and Monday morning. Good grief! And it was $326, which for me, is not that bad but it’s MB failure, not
mine.... !
Last edited by 2020GLC4Matic; May 11, 2026 at 09:19 PM.
Dealer repair/resolution: 78902 100 CONNECT BATTERY CHARGER , PERFORMED SDS TEST --CODE---> P019185 The rail pressure sensor has a malfunction. There is a signal above the permissible limit value , PERFORMED SOFTWARE UPDATE FOR M.E CONTROL UNIT AS PER FAULT CODE.
Is this something I could have done, a software update screws up my whole weekend and Monday morning. Good grief! And it was $326, which for me, is not that bad but it’s MB failure, not
mine.... !
OP, I am glad it was super easy fix. To answer your question, this type of software update requires using XENTRY which only those who have it, for example in this case a dealership will be able to perform. Glad it is resolved now.
Thanks @chrisbrown and @W205C43PFL . And what are your thoughts about paying for it, the more I think about it I say "no." I am calling the service manager and I think I have a right to question the charge. A manufacturer-required software update is often not something the owner should be paying for. The update falls under:
Recall (safety or emissions-related) which is 100% free by law.
Service campaign / goodwill update from the manufacturer. Q: is this a known issue and what details can I share back with the dealer?
Thanks @chrisbrown and @W205C43PFL . And what are your thoughts about paying for it, the more I think about it I say "no." I am calling the service manager and I think I have a right to question the charge. A manufacturer-required software update is often not something the owner should be paying for. The update falls under:
Recall (safety or emissions-related) which is 100% free by law.
Service campaign / goodwill update from the manufacturer. Q: is this a known issue and what details can I share back with the dealer?
Warranty-covered issue (extended warranty),
Any other thoughts on this?
Yes, you should ask why you were charged.
It sounds unusual to me, but did you ask for additional diagnostics while you were there?
You need to find out the reason for the charge, then you can decide to dispute it if you wish to do so.
Yes, you should ask why you were charged.
It sounds unusual to me, but did you ask for additional diagnostics while you were there?
You need to find out the reason for the charge, then you can decide to dispute it if you wish to do so.
Agree especially if OP have warranty, warranty should cover the diagnostic charge as well.
Thanks @chrisbrown and @W205C43PFL . And what are your thoughts about paying for it, the more I think about it I say "no." I am calling the service manager and I think I have a right to question the charge. A manufacturer-required software update is often not something the owner should be paying for. The update falls under:
Recall (safety or emissions-related) which is 100% free by law.
Service campaign / goodwill update from the manufacturer. Q: is this a known issue and what details can I share back with the dealer?
Warranty-covered issue (extended warranty),
Any other thoughts on this?
Replied above : ) hope they give you a proper work order.
Update: Issue Repaired by Dealer — But I'm Being Charged for a Software Update
The 2020 GLC300 was repaired by the dealer, and according to the invoice, the root cause was addressed under what appears to be a Mercedes service bulletin/campaign.
Customer complaint:
Check Engine Light illuminated
Vehicle would not accelerate properly
Engine stumbled/shuddered when stopped
Dealer repair notes:
A CLIENT STATES: CHECK ENGINE WARNING LIGHT ON AT DASH, WILL NOT ACCELERATE, WHEN AT A STOP VEHICLE STUMBLES
CAUSE: 541011 PERFORM QUICK TEST 350182 W (N/C)
476970 FUEL SYSTEM CONTROL UNIT REPLACE (AFTER CHECK) 350182 W (N/C)
547989 DISCONNECT/CONNECT GROUND LINEOF BATTERY FOR 12 V ON-BOARD ELECTRICAL SYSTEM (DURING REPAIR OPERATIONS) 350182 W (N/C)
1 000-545-01-41-64 EXCHANGE DIAGNOSTIC DEVICE
Further down the invoice:
G** SOFTWARE UPDATE NEED IT FOR CONTROL UNIT
55MBZ SOFTWARE UPDATE 350182 C
G** SOFTWARE UPDATE NEED IT FOR CONTROL UNIT
55MBZ SOFTWARE UPDATE 350182 C
Two separate software update entries were listed, and I was charged $325 for the software update.
The Service Manager told me Mercedes charges separately for software updates. My response was that this seems ridiculous if a software issue can cause the vehicle to go into limp mode, illuminate the check engine light, and require repair. Why should customers pay to correct a software problem that originated with Mercedes?
Has anyone successfully challenged a charge like this with Mercedes-Benz USA or the dealership? If so, what was your approach and what was the outcome?
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