Transmission disabled by CHASSIC RELAY HELP
Thread Starter
Newbie
Joined: Apr 2025
Posts: 3
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From: North Carolina
2008 C300 Sport
Transmission disabled by CHASSIC RELAY HELP
I drive a 2008 Mercedes C-300 Sport, w204: I accelerated from a green light, then immediately felt and heard loud noises coming from the drive train, transmission area, and torque conventor area. I towed the car home and jacked it up, all four wheels. I started the car and moved through the gear shift. The rear wheels turned very slow, regardless of the engine RPM. I also noticed that the wheel never rotated in the reverse position when the gear shift was placed in reverse. With my limited MB knowledge, I decided to purchase and install a used transmission, as my unit currently had 215 K miles on it with no routine maintenance. The used transmission was installed; I changed the filter and followed the manufacturer's refill process like a seasoned MB technician. During my final testing on the replacement unit, I realized that my replacement transmission was acting exactly like the original. (No gear engagement, slow wheel rotation, or reverse rotation. I started looking for an electrical issue and discovered that when I removed fuse number (33), a 10 amp fuse that sends power to the transmission TCM, the transmission then operated as usual (full gear engagement, in forward and reverse. The vehicle will drive. But the dash monitor displays the following message 
BRAKE, EBR, ABS, ESP inoperative).
It appears that Relay R, the CHASSIC Relay, is energized, sending power to the TCM, which is disabling the transmission operations.
In my scenario, what device or event would trigger the Chassic Relay to activate, cause the transmission to lock out with no operations
BRAKE, EBR, ABS, ESP inoperative).It appears that Relay R, the CHASSIC Relay, is energized, sending power to the TCM, which is disabling the transmission operations.
In my scenario, what device or event would trigger the Chassic Relay to activate, cause the transmission to lock out with no operations
MBWorld Fanatic!
Joined: Aug 2023
Posts: 3,703
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From: MA Coast
W204 2010 C300 4matic Sport M272
Not sure.
Heres the online manual for 2008 C300 if you want to look thru it. The Transmission and Drivetrain section has all the information about the car. https://charm.li/Mercedes%20Benz/200...d%20Diagnosis/
Heres the online manual for 2008 C300 if you want to look thru it. The Transmission and Drivetrain section has all the information about the car. https://charm.li/Mercedes%20Benz/200...d%20Diagnosis/
