Vacuum Supply, Function - GF42.22-P-1004LFH

Model 222.004/057/104/157/163/173 

Function requirements for vacuum supply in general 

• Electronic Stability Program control unit (N30/4) activated through wake-up function
• Circuit 15 ON

Vacuum supply, general 

The vacuum supply for the BAS brake booster (A7/7) is supported by the vacuum pump (M56).

Vacuum supply function sequence 

The vacuum supply ensures that there is always sufficient vacuum in the BAS brake booster (A7/7). When the combustion engine is running, this vacuum is generated by a mechanical vacuum pump which is driven by the engine.

When the combustion engine is off, in hybrid mode, the required vacuum is produced by the vacuum pump. The vacuum pump is actuated by the Electronic Stability Program control unit via the vacuum pump relay (K40/8kQ) and the brake vacuum pump relay (K40/8kI). When the ignition is switched on, the Electronic Stability Program control unit actuates the vacuum pump relay. The brake vacuum pump relay is only actuated when the vacuum in the BAS brake booster drops in hybrid driving mode. The vacuum in the BAS brake booster is registered by the brake vacuum sensor (B64/1) (up to model year 2018) or by the dual vacuum sensor (B150/2) (as of model year 2018). The Electronic Stability Program control unit reads in the signals directly and evaluates them.

Both vacuum pumps may operate for a brief transitional period of 1s. This is the case when the combustion engine is started while the vacuum pump is running.

In a stationary vehicle, the vacuum pump is not actuated. However, the vacuum pump is actuated if the vehicle is rolling with the ignition switched on. When there is a malfunction in the vacuum pump, when the combustion engine is off and the vacuum is dropping, the Electronic Stability Program control unit requests a forced engine start.

The brake vacuum pump relay is designed as a solid-state relay to achieve a faster response time and higher switching frequency. The difference compared with the vacuum pump relay is that mechanical parts are no longer used. A feedback line at the relay output is used by the Electronic Stability Program control unit to monitor the function of the brake vacuum pump relay.