Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Brief description of components
- IBS: Intelligent battery sensor
The IBS is a mechatronic, intelligent battery sensor with its own microcontroller.
The IBS continuously monitors the battery's:
- terminal voltage
- charge current
- discharge current
- Acid temperature
- MPM: Micro-power module
As from 09/2005, MPM function is integrated into the body-gateway module (KGM)
When the vehicle is at rest, the MPM switches individual consumers off, if:
- off-load current is high when the charge state is critical
- undervoltage occurs
- too many "wake-up" circuits are activated in the K-CAN
- the vehicle fails to go into sleep mode
the micro-power module is connected to the K-CAN.
- Rear power distributor with terminal 30g relay
The rear power distributor is installed on the right-hand side of the luggage compartment. The rear power distributor is connected to the positive terminal of the battery, the front power distributor and the external-start support point. The micro-power module (MPM) is supplied with power from the rear power distributor.
- Terminal 30g relay
The terminal 30g relay is actuated by the Car Access System (CAS) and prevents increased off-load current by switching off individual consumers.
- Power distributor, front
The front power distributor is connected to the rear power distributor. The CAS, the starter motor and the KGM are connected to the front power distributor. The body gateway module (KGM) is supplied with power from the front power distributor.
- Battery cables in outer floor area
The battery cable must be monitored on vehicles where the battery cable is installed on the underbody parallel to the fuel line. Depending on the type of vehicle, the battery cable is made from copper or aluminum and insulated with plastic. The insulation is mantled with low-impedance metal braiding. The metal braiding is the monitoring wire. The battery cable is then covered with a second insulation layer made from plastic. This is the external insulation layer.
A connection line is provided at both ends of the monitoring line.
- up to 09/2005:
The battery cables are monitored by the passive safety system ASE (advanced safety electronics) via satellites in the B-pillars. The end of the monitoring wire leads to the left-hand B-pillar satellite. The other end of the monitoring wire leads to the right-hand B-pillar satellite.
- from 09/2005:
The ASE is superseded by the ACSM ("Advanced Crash Safety Module", usually referred to as the "crash safety module").
The battery cable is monitored by the crash safety module. Both ends of the monitoring wire are connected to the crash safety module.
- Battery
The battery is installed on the right-hand side of the luggage compartment. The battery condition is continuously monitored by the IBS.
- Starting-aid terminal
The starting-aid terminal in the engine compartment is extension of the positive terminal of the battery to an easily accessible point.
- Ignition starter switch / START/STOP button
The ignition starter switch is superseded by the START/STOP button and the insert compartment for the remote control.
- CAS: Car access system
The CAS includes the following functions:
- Terminal control
- Electronic vehicle immobilizer (EWS)
- Evaluation of radio signals from remote control
The CAS is directly connected to ignition starter switch or insert compartment by wires. The DME / DDE and the starter motor are connected to the CAS. The CAS is part of the K-CAN bus network.
- DME or DDE: Digital engine electronics or digital diesel electronics
The DME/DDE is the engine control unit. The DME/DDE contains the electronic immobilizer (EWS). The DME/DDE is also used as a secondary (backup) data store. The DME/DDE is connected to the powertrain CAN (PT-CAN) data bus to allow it to communicate with other control units in the vehicle.
- Starter relay
The starter relay switches the battery voltage to the starter motor, when
- up to 09/2005:
The ignition starter switch is in switch position 2,
- from 09/2005:
The appropriate terminal is activated with the START/STOP button
- The CAS receives the correct information and transmits this to the DME / DDE via the K-CAN
- The electronic immobilizer (EWS) actuates the starter relay
- up to 09/2005:
- Starter motor
- up to 09/2005:
Battery voltage is fed to the starter motor via the starter relay to start the engine when the ignition starter switch is turned to position 2.
- from 09/2005
The START/STOP button can be used to switch the terminals in sequence (0, R, 15, R, 0).
- up to 09/2005:
- Alternator
When the engine is running, the alternator generates a variable charge voltage for battery charging. The power management system influences the variable charge voltage, depending on temperature and current, by causing the DME or DDE to increase the engine speed.
- Earth point on lightweight aluminum front end
The earth point on the lightweight aluminum front end (GRAV) is the place where steel body has its earth connection.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.