Automatic transmission vacuum control system in Mercedes-Benz 124
Components
* Vacuum modulator
* Vacuum wire
* Vacuum sensors on the throttle body and intake manifold
* Automatic transmission control valves
Operating principle
The automatic transmission vacuum control system uses engine vacuum to regulate pressure in the automatic transmission. The vacuum is transmitted to the vacuum modulator, which regulates the amount of vacuum transmitted to the automatic transmission control valves.
Sensors
The system uses two vacuum sensors:
* Throttle Position Sensor: Measures the throttle position and produces a vacuum signal proportional to the throttle position.
* Intake manifold pressure sensor: measures intake manifold pressure and produces a vacuum signal proportional to engine load.
Vacuum modulator
The vacuum modulator is the main component of the system. It regulates the amount of vacuum transmitted to the automatic transmission control valves. The modulator uses vacuum signals from sensors to determine when to shift gears.
Automatic transmission control valves
The automatic transmission control valves receive vacuum pressure from the vacuum modulator. They control the flow of transmission fluid into the automatic transmission, determining the timing of gear shifts.
Malfunctions
Problems with the automatic transmission vacuum control system can lead to shifting problems, vacuum leaks, or other automatic transmission problems.
Basic faults
* Vacuum wire leak
*Faulty throttle position sensor
* Faulty intake manifold pressure sensor
* Faulty vacuum modulator
* Faulty automatic transmission control valves
Diagnostics
Diagnostics of the automatic transmission vacuum control system requires the use of a pressure gauge and a vacuum sensor. Vacuum signals from the sensors and modulator are checked to ensure they meet specifications.
Repair
Repair of the automatic transmission vacuum control system usually includes the replacement of faulty components. These could be vacuum wires, sensors, a vacuum modulator or automatic transmission control valves.
It is important to have a qualified mechanic properly diagnose and repair the automatic transmission vacuum control system to ensure proper operation of the automatic transmission.