MSA and power management

The battery status that is calculated in the Advanced Power Management (APM) is a major influencing factor on the MSA. The APM monitors the following measured variables: battery charge state, battery temperature, voltage dip during engine start, power consumption of the switched-on consumer units.

In the event of engine shutdown, excessive power consumption must be avoided. To ensure this, at terminal 15 On and engine OFF the APM disables all large current consumer units or reduces their consumption. The displays remain active.
The following consumer units are affected:

• Heated rear window (demister)
  
• Mirror heating
  
• Seat heating
  
• Heater blower (the IHKA is responsible for adaptation of the heater blower).
  

Shutdown inhibitors

The MSA function is only possible if certain requirements are met. An MSA stop is prevented if environmental influences or vehicle conditions require this.
The following shutdown inhibitors are possible from the perspective of the APM:

• Battery charge state is not plausible.
  This can have the following possible causes:
  
  • The intelligent battery sensor (IBS) has been disconnected from the power supply or negative battery terminal. The battery charge state cannot be determined.
    
  • The IBS has a malfunction (e.g. communication fault with DME/DDE).
    
  • There is a sustained closed-circuit current fault and it prevents an open-circuit voltage measurement to determine the battery charge state.
    Find the cause of the closed-circuit current fault.
    
  • The vehicle is continuously in operation and did not have an adequately long off-load phase for an open-circuit voltage measurement to determine the battery charge state.
    Let the vehicle go to sleep and leave it in the off-load state for at least 1 hour.
    
  • An additional current consumer is directly connected to the battery and leads to a fault in determining the battery charge state by the IBS.
    
• The battery charge state is too low.
  The battery charge state does not correspond to the minimum state of charge required for MSA. The battery must be charged and troubleshooting continues with the test module <Energy diagnosis>.
  
• Battery temperature too high.
  The battery temperature is too high to reliably determine the battery charge state.
  
• Excessive voltage dip during the previous MSA engine start.
  The APM continuously monitors the on-board supply voltage and especially during the engine start. The voltage fell short of a threshold value during the previous MSA engine start.
  The battery temperature is too low or the battery is possibly poorly charged: recharge the battery and continue troubleshooting with the test module <Energy diagnosis>.
  
• Power consumption of the switched-on consumer units is too high.
  The switched-on current consumers require too much current: MSA stops are not permitted so that the battery can be supported by the alternator.
  Switch off large current consumers (e.g. heated rear window, seat heating or heater blower) so that MSA stop are permitted once again.
  

The current and last four shutdown inhibitors that occurred are stored in the data of the power management.
The power management also stores the last nine shutdown inhibitor types: if a shutdown inhibitor occurs a number of times in succession, it is only examined once.

Switch-on requesters

The fully automatic switch-on of the engine by MSA can also occur when the driver performs no action at all. Some vehicle conditions (switch-on requesters) require an immediate MSA engine start without action on the part of the driver.
The following switch-on requesters are possible from the perspective of the APM:

• During the MSA stop, the battery charge state falls short of the state of charge required for the MSA function. The engine is switched on again automatically to improve the charge balance.
  

The current and last four switch-on requesters that occurred are stored in the data of the power management.

Battery

For vehicles with automatic engine start-stop, an AGM battery must be fitted in all cases and it must be registered after battery replacement using the service function <Register battery replacement> so that the MSA function can work perfectly.

In the event of a battery replacement, disconnection of the battery or after programming the engine management system, the reference data for the battery charge state and battery condition can be lost.
They are only available again after an open-circuit voltage measurement of approx. 6 hours (e.g. off-load phase overnight) in which the vehicle may not be wakened. In this training period, the MSA function is not active (shutdown inhibitor = battery charge state not plausible). The customer is to be notified of this when the vehicle is handed over. The MSA function switches back automatically to active as soon as the necessary routines have been completed successfully.