HELP! GLC63s fan staying on
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Junior Member
Joined: Dec 2019
Posts: 42
Likes: 4
W205 C63s Coupe
HELP! GLC63s fan staying on
Ive been having an issue with my fan. As soon as the car turns on, the fan stays on at full power. It stays on at full power until the car reaches normal operating temperatures but the issue is the car never is able to reach normal operating temps because the fan just keeps the engine completely cooled down. Ive swapped out the fan, tried swapping the fan module, have had the wiring checked and now im out of ideas. I switched the car over to the stock tune to see if even that would help but it didn't the fan would still stay on the entire time. Does anyone have any ideas or suggestions on what to do next?
Junior Member
Joined: Sep 2022
Posts: 46
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AMG GLC 63S
Crazy this happened to you because my 2019 just spent 2 days being ripped apart at Mercedes Ottawa Downtown, for the EXACT SAME THING! Thank Jesus for warranty. I'm going to take a pic of the work order and put it here so you can cross reference. Ended up being a bad section of wire behind the firewall. Took 18 hours for them to find it.
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Joined: Aug 2020
Posts: 23
Likes: 13
2019 M2 Comp / 2013 Q5 / 2020 GLC63
I'll try and find my repair/work order and post, but I had something similar about 2-3k miles in on my 2020 GLC63.
Long story short, but similar to @Swissinn 's adventure - it took the dealer quite a long time to find the issue. ~17 hours if I recall.
Failure on mine was that one of the auxiliary intercooler pumps failed to a short on the communications bus side. The ECM couldn't talk to anything on that bus and went full speed on the fans to try and prevent what it thought could be a meltdown.
The dealer eventually found the issue. but because they couldn't use any diagnosis tools to readback the problem, there was a fair amount of disconnect/reconnect of devices on the bus to find the shorted one.
I tried not to read w/comprehension or memory engagement on how much had to come apart to get to everything because I'd be listening/looking for every nitpick sound or detail that wasn't the same as before the trip to dealer. I know the fender liners, front bumper cover and possibly left fender came off at a minimum.
In fairness, ~25k miles later and they did a pretty good job of getting it all back together. I've never seen any signs it had been ripped apart.
Long story short, but similar to @Swissinn 's adventure - it took the dealer quite a long time to find the issue. ~17 hours if I recall.
Failure on mine was that one of the auxiliary intercooler pumps failed to a short on the communications bus side. The ECM couldn't talk to anything on that bus and went full speed on the fans to try and prevent what it thought could be a meltdown.
The dealer eventually found the issue. but because they couldn't use any diagnosis tools to readback the problem, there was a fair amount of disconnect/reconnect of devices on the bus to find the shorted one.
I tried not to read w/comprehension or memory engagement on how much had to come apart to get to everything because I'd be listening/looking for every nitpick sound or detail that wasn't the same as before the trip to dealer. I know the fender liners, front bumper cover and possibly left fender came off at a minimum.
In fairness, ~25k miles later and they did a pretty good job of getting it all back together. I've never seen any signs it had been ripped apart.
Junior Member
Joined: Sep 2022
Posts: 46
Likes: 12
AMG GLC 63S
I'll try and find my repair/work order and post, but I had something similar about 2-3k miles in on my 2020 GLC63.
Long story short, but similar to @Swissinn 's adventure - it took the dealer quite a long time to find the issue. ~17 hours if I recall.
Failure on mine was that one of the auxiliary intercooler pumps failed to a short on the communications bus side. The ECM couldn't talk to anything on that bus and went full speed on the fans to try and prevent what it thought could be a meltdown.
The dealer eventually found the issue. but because they couldn't use any diagnosis tools to readback the problem, there was a fair amount of disconnect/reconnect of devices on the bus to find the shorted one.
I tried not to read w/comprehension or memory engagement on how much had to come apart to get to everything because I'd be listening/looking for every nitpick sound or detail that wasn't the same as before the trip to dealer. I know the fender liners, front bumper cover and possibly left fender came off at a minimum.
In fairness, ~25k miles later and they did a pretty good job of getting it all back together. I've never seen any signs it had been ripped apart.
Long story short, but similar to @Swissinn 's adventure - it took the dealer quite a long time to find the issue. ~17 hours if I recall.
Failure on mine was that one of the auxiliary intercooler pumps failed to a short on the communications bus side. The ECM couldn't talk to anything on that bus and went full speed on the fans to try and prevent what it thought could be a meltdown.
The dealer eventually found the issue. but because they couldn't use any diagnosis tools to readback the problem, there was a fair amount of disconnect/reconnect of devices on the bus to find the shorted one.
I tried not to read w/comprehension or memory engagement on how much had to come apart to get to everything because I'd be listening/looking for every nitpick sound or detail that wasn't the same as before the trip to dealer. I know the fender liners, front bumper cover and possibly left fender came off at a minimum.
In fairness, ~25k miles later and they did a pretty good job of getting it all back together. I've never seen any signs it had been ripped apart.
Thread Starter
Junior Member
Joined: Dec 2019
Posts: 42
Likes: 4
W205 C63s Coupe
Responding back to this post for anyone else also having a similar issue. Ended up taking it to the dealer after having 3 different mechanics look at it. Ended up being a split wire under the drivers carpet. Crazy to think something inside was causing it but if you have a trusted dealer, have them diagnose and repair it for you.
