Automatic Engine Start-Stop (Automatic Engine Start-Stop)
Engine Start Engine Start-Stop
The new function of automatic engine start-stop (MSA) is a fundamental component of the measures package to reduce CO2 emissions. The reduction in fuel consumption is achieved by automatic shutdown of the engine when the vehicle is at a standstill. The new start also takes place automatically as soon as the corresponding conditions required for switch-on are met.
The MSA will be deployed in the BMW 1 Series, 3 Series and MINI model series in conjunction with the manual transmission and four-cylinder engine.
NOTE: Bear in mind the designation used by marketing.
The marketing designation is automatic engine start-stop function.
MSA function, principle
The MSA ensures automated shutdown of the engine while the vehicle is being driven if the vehicle comes to a standstill and a number of essential vehicle conditions are met to enable this shutdown.
Examples (matrix, see "System functions"):
- Vehicle stationary
- No gear is engaged
- Clutch not pressed
- Engine temperature not too low
- Ambient temperature greater than 3 °C
- Brake vacuum sufficient
- Battery charge status adequately high
- Driver's seat belt fastened
- No backing up has taken place
Just as automatic as this shutdown is the automatic restart of the engine as soon as the clutch is pressed again or there are other requirements.
Sample scenario: switching off the engine at a standstill at a red traffic light or in stop-and-go traffic.
IMPORTANT:
The automatic switch on of the engine on vehicles with MSA can also take place when the driver takes no action. Customer annoyance and customer complaints are not based on a malfunction! Situations in which the engine starts fully automatically without any action on the part of the driver are, for example:
- A/C-request signal: e.g. windscreen fogged over.
- Insufficient brake partial vacuum: insufficient brake partial vacuum can lead to safety risks during braking manoeuvres. To prevent this, the engine is started.
- Stalling of the engine.
- Battery almost fully discharged: flat batteries can lead to a complete breakdown of the vehicle. To prevent this, the engine is started.
- Vehicle at a standstill on an incline starts to roll: when the vehicle is switched off, many systems are inactive. Rolling vehicles without the supporting effect of the vehicle systems are a safety risk. To prevent this, the engine is started.
Brief description of components
The MSA function is located in the engine electronics (DME or DDE). Various information from the bus systems is used for the MSA. New components are also necessary. The following components for the MSA are described:
- Zero gear sensor (new)
- Brake partial vacuum sensor (new)
- MSA button (new)
- DC/DC converter (new)
- AGM battery (new)
- Clutch Switch
- Bonnet contact switch
- Seat belt buckle contact (driver)
- Alternator
- Starter motor
Zero gear sensor
The zero gear sensor is mounted on top of the transmission case. The zero gear sensor detects the idle position of the gearstick.
Brake vacuum sensor
In order to ensure adequate brake power assistance in every situation, the brake booster is equipped with a partial vacuum sensor.
The brake partial vacuum sensor is located beside the brake booster and is connected via a separate cable.
IMPORTANT: With a brake partial vacuum that is too low, the MSA also starts without activity on the part of the driver. Insufficient brake partial vacuum can lead to safety risks during braking manoeuvres, e.g. when rolling on an incline. To prevent this, the engine is started.
MSA button
The MSA button (MSA OFF) on the centre console switch cluster can be used to deactivate the MSA function. With each terminal change "Terminal 15 On" or repeated pressing of the MSA button, the MSA is reactivated.
DC/DC converter
Due to the considerably more frequent occurrence of starting operations, the electrical load that occurs often leads to voltage dips in the vehicle network. In order to stabilize the power supply for certain voltage-sensitive electrical components, a DC/DC converter is used in conjunction with the MSA.
The DC/DC converter supplies the two relays "terminal 30g_DC/DC" and "terminal 30g-f_DC/DC" with a voltage that also remains constant during the starting operation.
The DC/DC converter is fitted in the E-box in the engine compartment.
Via the test leads for input voltage and terminal 50, the electronics decide whether the power is supplied to the output via the bypass or the DC/DC converter.
In the bypass mode, the on-board supply voltage is not fed across the DC/DC converter, rather is transferred directly to the outputs. In the booster phase, the vehicle voltage is adapted.
AGM battery
In all cases, the MSA comes with the intelligent alternator control. The much more frequent charge and discharge cycles mean that the load on the battery is very high. The cycle resistance of AGM batteries means that they achieve similar results with regard to service life despite the high load.
IMPORTANT: Ensure an AGM battery is fitted.
In all cases, an AGM battery must be installed and registered in the vehicle for the MSA to work perfectly.
Clutch Switch
The present clutch switch is used as an input variable for the MSA to detect clutch operation.
Bonnet contact switch
The bonnet contact switch is included as an influencing factor in the calculation of the MSA. If the engine bonnet opened, the engine must not be started or stopped by the MSA for safety reasons.
IMPORTANT:
- In the event of a defective bonnet contact switch, the MSA function is suppressed.
- If the bonnet contact switch is pulled upwards, the information "Switch closed" is displayed. The MSA is active and an automatic engine start can take place.
Belt buckle switch (driver)
Via the belt buckle switch, the MSA can detect that the driver has fastened his or her seat belt. If the driver has not fastened his or her seat belt, the MSA reacts as follows:
- With the engine running, a shutdown inhibitor is set.
- With MSA stop, the MSA is disabled. A new start is possible using the START-STOP button.
Alternator
The battery discharge during the engine shutdown by the MSA means that a more powerful alternator is installed.
Starter motor
In conjunction with the MSA, the starter motor must do a great deal more work. The starter motor is therefore configured for a significantly higher number (approx. 8 times) of start cycles. The components of the starter motor have been adapted to the higher requirements.
System functions
The following system functions for the MSA are described:
- System circuit diagram
- Operating strategy: Enable or shutdown of the MSA
- Display concept: Display in conjunction with the MSA
- Power management
System circuit diagram
Operating strategy: Enable or shutdown of the MSA
After every engine start, the function is automatically active and on stand-by. The MSA button (center console switching center) can be used to deactivate the function manually until the next terminal change. Pressing the button is confirmed by an LED lighting up.
During the diagnosis sessions, the MSA is temporarily disabled for safety reasons (this means until the next terminal change). This prevents the possibility of an automatic engine start during work in the engine compartment.
The status of a temporary shutdown can be read in the control-module functions at all times using "Detection shutdown MSA". Furthermore, the status of the non-detection of a vehicle with MSA can be read out in the control-module functions by means of "Check installation of MSA" as well as "Status coding MSA".
IMPORTANT: Pay attention to personal safety.
For reasons of personal safety, it must always be conscientiously determined that the engine start-stop function has been disabled before work in the engine compartment.
Shutdown request:
NOTE: Definition of comfort stop.
Low filling during comfort stop prevents the engine from "shaking". The comfort stop function empties the intake air collector (engine runs for 1 second longer).
Shutdown inhibitor:
Switch-on request (simultaneously locks the preparation for comfort stop on the N43):
Condition E8x, E9x, R55, R56
Clutch pressed more than 10 % X
Vehicle starting to roll X
Brake partial vacuum inadequate. X
Switch-on request from power management X
Switch-on request from A/C-request signal X
Switch-on inhibitor:
Condition E8x, E9x, R55, R56
No idling or clutch pedal X
not in end position
Engine just stopped X
(safety function to ensure
safe engine runout. Otherwise,
it can happen that the starter
motor engages in the engine
while it is still running out).
All conditions as well as general status information can be read out using the service function "system check MSA".
Reading out a history of the last stored shutdown inhibitors is possible by means of the service function "read AV memory". This enables a check of past customer complaints.
Display concept: Display in conjunction with the MSA
If the MSA has shut down the engine, a display appears in the instrument cluster.
The following symbol is shown in the LC display between the dials:
There are also 2 Check Control messages available for the MSA.
A Check Control message appears if a system fault (with or without necessary component replacement) is active or the MSA is disabled.
Corresponding reading options are available through the service functions "system check MSA" as well as "read AV memory".
Other service functions serve as additional plausibility checks and checks of the function characteristics (exception: learn / write zero gear sensor).
Power management
The battery status that is calculated in the Advanced Power Management (APM) is a major influencing factor on the MSA.
The aim is to enable a reliable start of the combustion engine after a defined parking period from the perspective of the vehicle energy system.
The APM monitors the following data:
- Battery charge condition
- Battery temperature
- Voltage dip on engine start
- Power requirement of switched-on consumer units
The result of the calculation can be a shutdown inhibitor or a switch-on request of the MSA.
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 consumer units or reduces their consumption. The displays remain active.
The following consumer units are affected:
- Rear-window defroster (demister)
- Mirror heating
- Seat heating
- Heater fan
IMPORTANT: Automatic starting is possible.
If the battery charge state drops after an MSA engine shutdown to below a certain limit, the MSA starts the engine even without any action on the part of the driver.
Note for Service department:
General information
The MSA only works when certain requirements are met (see Operating conditions). In the event of a customer complaint, these requirements must always be checked.
Automatic shut-down at terminal 15 as of 03/2007 in vehicles with automatic engine start-stop function (MSA - optional extra 1CC).
Opening or closing the driver's door (engine OFF) automatically switches off terminal 15 via the signal from the door contact.
By subsequently pressing the START-STOP button, terminal 15 can be switched on again permanently.
Run this operation before programming or diagnosing a vehicle.
Replacement of the zero gear sensor
Replacement of the zero gear sensor may only be carried out according to the instructions in the service function "learn/write zero gear sensor". Without correct installation of the sensor, the functionality is inactive or faulty.
Be sure to comply with safety measures for work on vehicles with MSA.
Always ensure that the MSA has been switched off in order to prevent an automatic engine start during work in the engine compartment.
Faults for the MSA
Stored faults for the MSA deactivate the automatic engine start-stop.
MSA and power management
The MSA is strongly networked with the power management. In the event of battery replacement, disconnection of the battery or after programming the engine management system, the reference data regarding the battery charge state and battery condition can be lost.
They are only available again after a closed-circuit current measurement of approx. 6 hours (e.g. closed-circuit current measurement overnight without connected charger) in which the vehicle may not be wakened. In this time, the MSA is inactive.
The customer must be notified of this when the vehicle is handed over. The MSA switches back automatically to active as soon as the necessary routine have been completed successfully.
Diagnosis instructions
The following test modules exist to check the components:
- Zero gear sensor
- brake partial vacuum sensor
- Clutch Switch
- MSA button (networked with centre console switch cluster)
- Door contact MSA (networked with FRM)
- DC/DC converter (networked with JBE)
- Power management MSA (information on the vehicle energy system and the last shutdown inhibitors or switch-on requesters from power management)
The service function "read AV memory" can be used to read out a history of the last stored shutdown inhibitors.