The P0757 code in your 2019 Mercedes-Benz C-Class indicates that shift solenoid B is stuck in the on position. This is the opposite of P0756—the solenoid is continuously activated when it should be able to turn off. Your C-Class uses a 9G-TRONIC 9-speed automatic where this causes gear selection conflicts.
Shift Solenoid B Stuck On Effects
When solenoid B is stuck on, the hydraulic circuit it controls remains engaged continuously. This can cause the transmission to stay in certain gears, skip others, or have conflicts between gear applications. The specific effect depends on which gears require solenoid B off.
Common Causes
A mechanically stuck solenoid that won't return to off. Valve stuck in the applied position due to debris or wear. Electrical short keeping the solenoid energized. Valve body issues trapping the solenoid valve. Spring failure inside the solenoid preventing return.
Symptoms in Your C-Class
The transmission may have difficulty with certain gear changes. Harsh shifts in gears that conflict with the stuck-on solenoid. The transmission may skip gears or start in the wrong gear. Possible gear ratio codes as the TCM detects conflicts. Check engine light with P0757 stored.
Mercedes Diagnostic Process
Using Mercedes-Benz XENTRY, monitor shift solenoid B state versus commanded state. Check for gear conflicts when solenoid B should be off. Test solenoid valve movement—it should move freely when de-energized. Inspect valve body for stuck valves. Check 9G-TRONIC fluid level and condition.