Brand new 2020 GLC check engine light
Thread Starter
Newbie
Joined: Jul 2020
Posts: 3
Likes: 0
2020 GLC-300
Brand new 2020 GLC check engine light
Hello all,
I was thrilled to pick up my new fully loaded black/black 2020 GLC-300 last week and have simply loved every minute so far.... Until this morning when the check engine light came on and it began emitting a high pitch whine at all RPM’s, including idle. Yes, the gas cap is on correctly. A total of 150 miles on it so far, so I’m in a little bit of disbelief I’m already having a major issue. I didn’t find anything in the forums about this so hoping it’s a one-off problem and I didn’t just buy a sharp looking lemon.
any ideas what the problem could be? We dropped it off at a dealer tonight (actually not the same one we purchased it from because they refused to call us back). Just getting the car was an ordeal as it was delayed from the VPC, hoping that isn’t a harbinger of things to come.
-blankreality
I was thrilled to pick up my new fully loaded black/black 2020 GLC-300 last week and have simply loved every minute so far.... Until this morning when the check engine light came on and it began emitting a high pitch whine at all RPM’s, including idle. Yes, the gas cap is on correctly. A total of 150 miles on it so far, so I’m in a little bit of disbelief I’m already having a major issue. I didn’t find anything in the forums about this so hoping it’s a one-off problem and I didn’t just buy a sharp looking lemon.
any ideas what the problem could be? We dropped it off at a dealer tonight (actually not the same one we purchased it from because they refused to call us back). Just getting the car was an ordeal as it was delayed from the VPC, hoping that isn’t a harbinger of things to come.
-blankreality
Super Member
Joined: Apr 2020
Posts: 682
Likes: 90
19 GLC300 4M (lunar blue/black/black ash aluminum),17 GLE350 4M (selenite grey/ espresso/eucalyptus)
Hello all,
I was thrilled to pick up my new fully loaded black/black 2020 GLC-300 last week and have simply loved every minute so far.... Until this morning when the check engine light came on and it began emitting a high pitch whine at all RPM’s, including idle. Yes, the gas cap is on correctly. A total of 150 miles on it so far, so I’m in a little bit of disbelief I’m already having a major issue. I didn’t find anything in the forums about this so hoping it’s a one-off problem and I didn’t just buy a sharp looking lemon.
any ideas what the problem could be? We dropped it off at a dealer tonight (actually not the same one we purchased it from because they refused to call us back). Just getting the car was an ordeal as it was delayed from the VPC, hoping that isn’t a harbinger of things to come.
-blankreality
I was thrilled to pick up my new fully loaded black/black 2020 GLC-300 last week and have simply loved every minute so far.... Until this morning when the check engine light came on and it began emitting a high pitch whine at all RPM’s, including idle. Yes, the gas cap is on correctly. A total of 150 miles on it so far, so I’m in a little bit of disbelief I’m already having a major issue. I didn’t find anything in the forums about this so hoping it’s a one-off problem and I didn’t just buy a sharp looking lemon.
any ideas what the problem could be? We dropped it off at a dealer tonight (actually not the same one we purchased it from because they refused to call us back). Just getting the car was an ordeal as it was delayed from the VPC, hoping that isn’t a harbinger of things to come.
-blankreality
1: turbo failure. Not common, this problem might have something to do with the sound.
2: computer system malfunction. Self explanatory
3: you bought a 🍋. Now get rid of it as fast as possible.
Super Member
Joined: Apr 2020
Posts: 682
Likes: 90
19 GLC300 4M (lunar blue/black/black ash aluminum),17 GLE350 4M (selenite grey/ espresso/eucalyptus)
I can help you diagnose turbo failure. You will need someone to be there
step 1 - start car, send other person to back of the car.
step 2 - place one foot on brake and hold
step 3 - place other foot on gas
step 4 - rev
step 5 - slowly release gas, when revs drop fully, turn off engine.
step 6 - ask other person if there was a load of exhaust smoke or any discoloration in the smoke.
step 7 - if answer is yes, your car may have turbo failure.
step 1 - start car, send other person to back of the car.
step 2 - place one foot on brake and hold
step 3 - place other foot on gas
step 4 - rev
step 5 - slowly release gas, when revs drop fully, turn off engine.
step 6 - ask other person if there was a load of exhaust smoke or any discoloration in the smoke.
step 7 - if answer is yes, your car may have turbo failure.
Last edited by ParjAS; Jul 14, 2020 at 01:56 PM. Reason: Format
Super Member
Joined: Apr 2020
Posts: 682
Likes: 90
19 GLC300 4M (lunar blue/black/black ash aluminum),17 GLE350 4M (selenite grey/ espresso/eucalyptus)
I can help you diagnose turbo failure. You will need someone to be there
step 1 - start car, send other person to back of the car.
step 2 - place one foot on brake and hold
step 3 - place other foot on gas
step 4 - rev
step 5 - slowly release gas, when revs drop fully, turn off engine.
step 6 - ask other person if there was a load of exhaust smoke or any discoloration in the smoke.
step 7 - if answer is yes, your car may have turbo failure.
step 1 - start car, send other person to back of the car.
step 2 - place one foot on brake and hold
step 3 - place other foot on gas
step 4 - rev
step 5 - slowly release gas, when revs drop fully, turn off engine.
step 6 - ask other person if there was a load of exhaust smoke or any discoloration in the smoke.
step 7 - if answer is yes, your car may have turbo failure.
Super Member
Joined: Apr 2020
Posts: 682
Likes: 90
19 GLC300 4M (lunar blue/black/black ash aluminum),17 GLE350 4M (selenite grey/ espresso/eucalyptus)
You might want to look at this: https://mbworld.org/forums/c450-c43-...ine-light.html. They had similar problem! 
Super Member
Joined: Apr 2020
Posts: 682
Likes: 90
19 GLC300 4M (lunar blue/black/black ash aluminum),17 GLE350 4M (selenite grey/ espresso/eucalyptus)
I wouldn't be worried. I know it is scary for your cel to come on but hey, you still have warranty to fix any crap lurking under the engine. Personally, I would have it repaired as soon as possible. Just have your fingers crossed that warranty has it covered.
Trending Topics
MBWorld Fanatic!
Joined: Nov 2012
Posts: 6,130
Likes: 1,117
A gaggle of MB's
Well, please don't let these troglodytes who obviously have zero experience and even less common sense.
If you refilled your tank - odd's are it is a loose gas cap - if you haven't refueled - then odd's are it is simply another minor thing.
When I say "odd's are" - I mean over 9-out-of-10
If you refilled your tank - odd's are it is a loose gas cap - if you haven't refueled - then odd's are it is simply another minor thing.
When I say "odd's are" - I mean over 9-out-of-10
MB World Stories
The Best of Mercedes & AMG
6 Mercedes Models That Did NOT Age Well (But Are Somehow Still Cool)
Verdad Gallardo
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
MBWorld Fanatic!
Joined: Oct 2018
Posts: 3,360
Likes: 1,529
From: Washington DC
No more MB:(
You have 150 miles on it, it's essentially brand new, take it to the dealer. Are you really going to self diagnose and fix it? Not a big deal. Probably a sensor or software.
Super Member
Joined: Apr 2020
Posts: 682
Likes: 90
19 GLC300 4M (lunar blue/black/black ash aluminum),17 GLE350 4M (selenite grey/ espresso/eucalyptus)
Well, please don't let these troglodytes who obviously have zero experience and even less common sense.
If you refilled your tank - odd's are it is a loose gas cap - if you haven't refueled - then odd's are it is simply another minor thing.
When I say "odd's are" - I mean over 9-out-of-10
If you refilled your tank - odd's are it is a loose gas cap - if you haven't refueled - then odd's are it is simply another minor thing.
When I say "odd's are" - I mean over 9-out-of-10
Super Member
Joined: Apr 2020
Posts: 682
Likes: 90
19 GLC300 4M (lunar blue/black/black ash aluminum),17 GLE350 4M (selenite grey/ espresso/eucalyptus)
I don't think that a gas cap could cause high pitched whine... That being said, it could just be something in the c43 forums link I had posted earlier.
Super Member
Joined: Apr 2020
Posts: 682
Likes: 90
19 GLC300 4M (lunar blue/black/black ash aluminum),17 GLE350 4M (selenite grey/ espresso/eucalyptus)
My thoughts exactly. I would take it to the dealer anyway. It is harder to self diagnose. Also, the more and more tech you add, the more things go bad. One final thought, is your a.c. compressor good? That might be where the whine came from.
Super Member
Joined: Dec 2016
Posts: 641
Likes: 226
From: Charlotte, NC
2024 E450 AT Wagon, 2024 EQS450+ / Had: 2021 E350, 2019 E300, 2021 + 20 GLE350, 2019 E450 Wagon(s)
So - the check engine light was on at delivery when I picked up my 2017 E300 with 17 miles on it. I took the car anyway so the dealer could book the sale for the month and they picked it up a few days later to fix it. They had it a week, it came back perfect and I never had another issue with it - so, take it back, they will fix it and you will go back to enjoying your new GLC.
Super Member
Joined: Apr 2020
Posts: 682
Likes: 90
19 GLC300 4M (lunar blue/black/black ash aluminum),17 GLE350 4M (selenite grey/ espresso/eucalyptus)
So is this a common problem with MB I-4 and I-6/V6 petrol/gas models (200, 220, 250, 300, 350, 400, 450, AMG 35, AMG 43, AMG 45, AMG 53)?
Thread Starter
Newbie
Joined: Jul 2020
Posts: 3
Likes: 0
2020 GLC-300
Update:
So I took the car back to the dealer and they diagnosed a bad purge valve. Sounds like a reasonable small thing to fix, all under warranty. Took them about 5 days to obtain and replace the part and they kept it for an extra day "for additional testing" which I assume was the 20 extra miles they put on it. Got the car back on Friday and drove it around 20 miles this weekend. Check engine light comes on *AGAIN* today...no abnormal sounds from what I can tell this time. Beyond livid and now looking up my state lemon laws. Makes me wonder if it is something else in the EVAP system down stream of the valve that could be causing it to fail? When I take it back to the dealer again I'm going to ask them for the specific codes that are showing up to hopefully get some more insight into the problem. The saga continues....
So I took the car back to the dealer and they diagnosed a bad purge valve. Sounds like a reasonable small thing to fix, all under warranty. Took them about 5 days to obtain and replace the part and they kept it for an extra day "for additional testing" which I assume was the 20 extra miles they put on it. Got the car back on Friday and drove it around 20 miles this weekend. Check engine light comes on *AGAIN* today...no abnormal sounds from what I can tell this time. Beyond livid and now looking up my state lemon laws. Makes me wonder if it is something else in the EVAP system down stream of the valve that could be causing it to fail? When I take it back to the dealer again I'm going to ask them for the specific codes that are showing up to hopefully get some more insight into the problem. The saga continues....
MBWorld Fanatic!
Joined: Oct 2018
Posts: 3,360
Likes: 1,529
From: Washington DC
No more MB:(
Update:
So I took the car back to the dealer and they diagnosed a bad purge valve. Sounds like a reasonable small thing to fix, all under warranty. Took them about 5 days to obtain and replace the part and they kept it for an extra day "for additional testing" which I assume was the 20 extra miles they put on it. Got the car back on Friday and drove it around 20 miles this weekend. Check engine light comes on *AGAIN* today...no abnormal sounds from what I can tell this time. Beyond livid and now looking up my state lemon laws. Makes me wonder if it is something else in the EVAP system down stream of the valve that could be causing it to fail? When I take it back to the dealer again I'm going to ask them for the specific codes that are showing up to hopefully get some more insight into the problem. The saga continues....
So I took the car back to the dealer and they diagnosed a bad purge valve. Sounds like a reasonable small thing to fix, all under warranty. Took them about 5 days to obtain and replace the part and they kept it for an extra day "for additional testing" which I assume was the 20 extra miles they put on it. Got the car back on Friday and drove it around 20 miles this weekend. Check engine light comes on *AGAIN* today...no abnormal sounds from what I can tell this time. Beyond livid and now looking up my state lemon laws. Makes me wonder if it is something else in the EVAP system down stream of the valve that could be causing it to fail? When I take it back to the dealer again I'm going to ask them for the specific codes that are showing up to hopefully get some more insight into the problem. The saga continues....
Thread Starter
Newbie
Joined: Jul 2020
Posts: 3
Likes: 0
2020 GLC-300
Update #2
Update!
We returned to the dealership and the second error code was P045600, a small leak in the EVAP system. The tech stated the valve replaced last time checked out fine. After speaking to the service manager he said this is a known issue with the GLC due to a redesigned carbon canister in the system which seems to have a design flaw. He said there may be a technical bulletin about this issue (I was unable to find this online but who knows). He obtained a new carbon canister which apparently has an updated design and replaced it. 30 miles of test driving later we got the car back. So far so good in the 5 days we've been driving it since we got it back. He also took the somewhat unusual extra step of advising me to get back in contact with the sales rep who sold us the car if there are any additional issues.
Fingers crossed this is last of the problems for the next 100k miles!
Thanks for the input!
We returned to the dealership and the second error code was P045600, a small leak in the EVAP system. The tech stated the valve replaced last time checked out fine. After speaking to the service manager he said this is a known issue with the GLC due to a redesigned carbon canister in the system which seems to have a design flaw. He said there may be a technical bulletin about this issue (I was unable to find this online but who knows). He obtained a new carbon canister which apparently has an updated design and replaced it. 30 miles of test driving later we got the car back. So far so good in the 5 days we've been driving it since we got it back. He also took the somewhat unusual extra step of advising me to get back in contact with the sales rep who sold us the car if there are any additional issues.
Fingers crossed this is last of the problems for the next 100k miles!
Thanks for the input!
Super Member
Joined: Apr 2020
Posts: 682
Likes: 90
19 GLC300 4M (lunar blue/black/black ash aluminum),17 GLE350 4M (selenite grey/ espresso/eucalyptus)
Update!
We returned to the dealership and the second error code was P045600, a small leak in the EVAP system. The tech stated the valve replaced last time checked out fine. After speaking to the service manager he said this is a known issue with the GLC due to a redesigned carbon canister in the system which seems to have a design flaw. He said there may be a technical bulletin about this issue (I was unable to find this online but who knows). He obtained a new carbon canister which apparently has an updated design and replaced it. 30 miles of test driving later we got the car back. So far so good in the 5 days we've been driving it since we got it back. He also took the somewhat unusual extra step of advising me to get back in contact with the sales rep who sold us the car if there are any additional issues.
Fingers crossed this is last of the problems for the next 100k miles!
Thanks for the input!
We returned to the dealership and the second error code was P045600, a small leak in the EVAP system. The tech stated the valve replaced last time checked out fine. After speaking to the service manager he said this is a known issue with the GLC due to a redesigned carbon canister in the system which seems to have a design flaw. He said there may be a technical bulletin about this issue (I was unable to find this online but who knows). He obtained a new carbon canister which apparently has an updated design and replaced it. 30 miles of test driving later we got the car back. So far so good in the 5 days we've been driving it since we got it back. He also took the somewhat unusual extra step of advising me to get back in contact with the sales rep who sold us the car if there are any additional issues.
Fingers crossed this is last of the problems for the next 100k miles!
Thanks for the input!
