The suction jet pump serves the purpose of generating the vacuum necessary for the brake booster. When no power is applied, the suction jet pump valve is open and has a brake pressure boosting effect. Depending on the engine temperature and selector lever position, power is applied to the valve of the suction jet pump when the vacuum is at sufficient levels even without the suction jet pump.
The suction jet pump valve is installed on the M52 with the MS42 only in the E46 up to 4/98 and on the M43 with BMS46 only in vehicles with automatic transmission. The suction jet pump is constantly effective in all other models.