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2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
KEYLESS-GO Stopped Working Suddenly
For no apparent reason, my KEYLESS-GO (KG) totally stopped working in my 2015 SL400. Neither of my key fobs were able to lock/unlock or start the car with Push Start. When I got into the car, the fobs were not detected. However, the fobs did work in the ignition switch to start the car the old-fashioned way. (I thought I was living in a 3rd World country and was embarassed someone would see me physically inserting and turning a key.)
Scanned for codes using my LAUNCH Creader Elite 2.0 BENZ -- no faults/codes. Broke out and fired up my XENTRY from @BenzNinja -- no faults or codes (per se) but also no KG module was detected. However, there were two CAN Bus related faults in Central Gateway (CGW).
I reached out to Peter (BenzNinja) who suggested I check the fuse. The fuse was arguably good (not blown). (In the R231 cars, the fuse for KEYLESS-GO is #74 which is in the fuse panel behind the passenger seat. It is a 10 Amp fuse.)
I replace the fuse anyway. SURPRISE! Everything worked again. I checked continuity on the removed fuse and it was good.
My conclusion is that because KEYLESS-GO is ALWAYS powered, simply turning the car off and on does nothing to the power going to the KGmodule. But removing and replacing the fuse performed a hard reset of the KG module.
So, if you find yourself in this situation, remove and reinsert the unblown fuse and see if that resets everything.
For no apparent reason, my KEYLESS-GO (KG) totally stopped working in my 2015 SL400. Neither of my key fobs were able to lock/unlock or start the car with Push Start. When I got into the car, the fobs were not detected. However, the fobs did work in the ignition switch to start the car the old-fashioned way. (I thought I was living in a 3rd World country and was embarassed someone would see me physically inserting and turning a key.)
Scanned for codes using my LAUNCH Creader Elite 2.0 BENZ -- no faults/codes. Broke out and fired up my XENTRY from @BenzNinja -- no faults or codes (per se) but also no KG module was detected. However, there were two CAN Bus related faults in Central Gateway (CGW).
I reached out to Peter (BenzNinja) who suggested I check the fuse. The fuse was arguably good (not blown). (In the R231 cars, the fuse for KEYLESS-GO is #74 which is in the fuse panel behind the passenger seat. It is a 10 Amp fuse.)
I replace the fuse anyway. SURPRISE! Everything worked again. I checked continuity on the removed fuse and it was good.
My conclusion is that because KEYLESS-GO is ALWAYS powered, simply turning the car off and on does nothing to the power going to the KGmodule. But removing and replacing the fuse performed a hard reset of the KG module.
So, if you find yourself in this situation, remove and reinsert the unblown fuse and see if that resets everything.
My wife had a similar Keyless Go issue on her 2014 E550. In her case, the fuse was blown. The Keyless go circuit also powered the trunk "kick to open" feature, which had a pinched wire from when the previous owner replaced the rear bumper cover. I agree with JettaRed, it is poverty inducing when you need to remove the button and insert the key on a keyless go car!
KeylessGo was one of the very first things I got to tackle myself on new car while covered by factory warranty.
The keyless was too flakey, doors would unlock and still sound alarm...
Later on I found out what JR explained about the always powered modules: these sleepless modules are responsible for battery drain while parked.
These cars are carefully crafted to fail reliably. Starting up with low battery voltage tanks every networked module into gremlin territory.
Long story short... don't just reboot chassis, resolder keyless loose pins.
Then your keyless operation will work nearly well (EIS, DCU) - Everything dealing with door lock security is built to be barely stable. That keeps CAN-B awake too long during key poling = DRAIN! (sponsored by Varta)
Engine also benefit from reboot but unrelated to KG
short term: reboot to sanitize chaos
Long term: Solder CAN-B collection of solderless : EIS, KG, DCU
Last edited by CaliBenzDriver; Apr 30, 2025 at 12:04 AM.
KeylessGo was one of the very first things I got to tackle myself on new car while covered by factory warranty.
The keyless was too flakey, doors would unlock and still sound alarm...
Later on I found out what JR explained about the always powered modules: these sleepless modules are responsible for battery drain while parked.
These cars are carefully crafted to fail reliably. Starting up with low battery voltage tanks every networked module into gremlin territory.
Long story short... don't just reboot chassis, resolder keyless loose pins.
Then your keyless operation will work nearly well (EIS, DCU) - Everything dealing with door lock security is built to be barely stable. That keeps CAN-B awake too long during key poling = DRAIN! (sponsored by Varta)
Engine also benefit from reboot but unrelated to KG
short term: reboot to sanitize chaos
Long term: Solder CAN-B collection of solderless : EIS, KG, DCU
Well like our tablet, re-boot is good.
Even my Nvidia Shield this one : https://www.nvidia.com/en-us/shield/
Must be re-booted sometimes when it goes dummy and I can remove power totally.
I unplugged my battery so often every year, sometimes for minutes, sometime days, sometime weeks = good reboot heheheheh
Thus less glitch.
Well like our tablet, re-boot is good.
Even my Nvidia Shield this one : https://www.nvidia.com/en-us/shield/
Must be re-booted sometimes when it goes dummy and I can remove power totally.
I unplugged my battery so often every year, sometimes for minutes, sometime days, sometime weeks = good reboot heheheheh
Thus less glitch.
Especially linux systems like Android, does that run Android?
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Here's the issue. Many of these controllers are "buried" under a bunch of stuff. Here is the KG controller for the R231 SL. I will look to see how hard it is to get to it. I know already it means taking the trunk apart. I will also check the WIS for instructions.
Here's the issue. Many of these controllers are "buried" under a bunch of stuff. Here is the KG controller for the R231 SL. I will look to see how hard it is to get to it. I know already it means taking the trunk apart. I will also check the WIS for instructions.
JR, we'll help you fix this under 30mn.
This is a 10mn job + 5mn soldering + 10mn documenting pictures .
In W212 KG lives up above R-SAM
Passenger trunk side
Well. This is interesting. I was just about to create an alternator/voltage thread (which I likely still need to) but was searching keyless issues as just today I received a friendly "key not detected" message while doing hwy speeds for maybe 10 seconds. It went away & no symptoms other than the message itself were present.
Once home, I did a scan with my iCarsoft MB V2 & had those same CAN faults also in my Central Gateway (which have been historic & intermittently shown up recently), along with an "Internal Electrical Fault" in my SG-FOND Rear Control Module, even though that was recently replaced and had a Xentry/Star session with my Benz indy who I turn to for that which I don't have tools for, like alignments or Star. Although my issue may be far more nuanced, at least I can now pray that my keyless go module is intermittently sucking the life out of my battery & removal and/or replacement of the fuse is in order.
Jetta, any chance you've ever noticed a significant voltage drop just from unlocking and opening your doors? These voltage issues make your soldering method quite tempting. If all else fails, at least the car can just get the torch!!
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