Switch-off inhibitors, switch-on requesters and deactivators

Different conditions may affect the automatic engine start-stop function:

• Switch-off inhibitor: Engine is not stopped by the automatic engine start-stop
• Switch-on requester: Stopped engine is started by the automatic engine start-stop
• Deactivator: Automatic Start/Stop function is deactivated.

The individual statuses of the automatic engine start-stop function can be read out with the service function MSA system check  .

Switch-off inhibitors 

Under certain conditions the automatic engine start-stop function must be suppressed:

• Vehicle is rolling (only vehicles with manual transmission)
• Vacuum for the brake power assistance too low (only vehicles with manual gearbox)
• Brake pedal not operated firmly enough, the vehicle is therefore not detected as being sufficiently stopped (only vehicles with automatic transmission)
• Vehicle is stopped on inclines/downhill gradients > 12 %
• Applied steering angle > 6°
• Steering wheel movement not completed (otherwise insufficient steering servo)
• Vehicle with manual transmission was not driven with speed > 5 km/h after last engine shutdown
• Vehicle with automatic transmission was not driven with speed > 9 km/h after last engine shutdown
• Engine not running at idle speed (accelerator pedal is operated)
• Reversing
• Engine operating temperature too low
• Carbon canister is being flushed
• Inadequate fuel grade
• Active transmission adaptation (only vehicles with automatic transmission)
• Hydraulic impulse storage not yet loaded (only vehicles with automatic transmission)
• Stop-and-go traffic
• State of charge of the battery too low
• Ambient temperature below +3 °C
• Ambient temperature above +30 °C (with heating and air conditioning system switched on)
• Rain-light-solar-condensation sensor identifies condensation on the windscreen
• Heating and air conditioning system switched on, however passenger compartment not correspondingly heated up or cooled down
• Braking occurred with Antilock Brake System.

Switch-on prompts 

It may also be necessary to start the engine when:

• Vehicle is not stopped sufficiently by released brake pedal (only vehicles with automatic transmission)
• Steering wheel is moved
• Engine not running at idle speed (accelerator pedal is operated)
• Transmission changes from P to D. Previously, the driver had to change from position D to position P to take his foot from the brake pedal while the engine was automatically stopped (only vehicles with automatic transmission).
• Transmission changes from D to N or R (only vehicles with automatic transmission)
• Vacuum for the brake power assistance too low (only vehicles with manual gearbox)
• State of charge of the battery too low
• Ambient temperature above +30 °C (with heating and air conditioning system switched on)
• Rain-light-solar-condensation sensor identifies condensation on the windscreen
• Evaporator temperature too low to guarantee sufficient climate control
• Special case: driver's seat belt is still fastened and driver's door is opened (for instance when using a dummy in regions without mandatory seat belt usage).

Deactivators 

When a precondition for deactivation is present the automatic engine start-stop is deactivated.

The scenarios below are produced dependent upon when a precondition for deactivation has occurred for the automatic engine start-stop:

• Engine still runs and is no longer automatically stopped
• Engine was automatically stopped and starts again automatically
• Engine was automatically stopped and started, no longer automatic (the Check Control message "Automatic engine start-stop function OFF" is shown and the automatic engine start-stop function button must be operated for the engine start).

The following deactivators may occur:

• Driver absence detected
• Engine start did not take place after starting
• Engine compartment lid unlocked
• Fault relevant to automatic engine start-stop on engine, transmission or components involved in automatic engine start-stop was detected
• Bus communication malfunction
• Automatic engine start-stop function has been deactivated by the automatic engine start-stop function button
• Automatic engine start-stop was deactivated by diagnosis system
• Vehicle is in transport mode
• Engine was stopped.

An example of deactivation with subsequent switch-on request:

1. At automatic engine shutdown, the automatic engine start-stop function is deactivated by the automatic engine start-stop function button
2. The engine starts automatically
3. There is no further automatic engine shutdown as the automatic engine start-stop remains deactivated.
   NOTE: Read out history memory
   The service function MSA system check  can be used to read out the history of the automatic engine start-stop function.