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Alternator Interface Function - GF07.10-P-1009KJ
ENGINE 281.910 in MODEL 453.0/3/4
Function requirements for the alternator interface, general points
- Circuit 87 (Engine management ON)
- Engine runs
Alternator interface, general points
Messages are exchanged between the driver-side SAM control unit (N1011) and the alternator (G2) via the drive LIN (LIN C1) and communicates via the interior CAN (CAN B) with the ME-SFI [ME] control unit (N3/10) and therefore controls the control response of the alternator. To do this there is delayed adaptation of the charging voltage for a larger change in load of the alternator. The current operating rate of the alternator is transmitted by the driver-side SAM control unit to the ME-SFI [ME] control unit. The ME-SFI [ME] control unit reads in the following signals:
- Crankshaft position sensor (L5), engine speed
- On-board electrical system battery (G1), on-board electrical system voltage over "circuit 30"
- Alternator, status via driver-side SAM control unit and interior CAN
Function sequence for alternator interface
The control response of the alternator is communicated between the ME-SFI [ME] control unit and the driver-side SAM control unit.
the ME-SFI [ME] control unit and the driver-side SAM control unit control the following functions:
- Adapting the charging voltage with a delay in the event of frequent load changes at the alternator in idle to stabilize the idling speed.
- Protecting the alternator against overheating.
- Recognized errors via the interior CAN to the IC control unit (IC) (A1), for actuation of the respective indicator lamps and display messages.
- The ME-SFI [ME] control unit calculates the specified value of the charging voltage for optimal running of the alternator.
- The driver-side SAM control unit transmits the charge level of the on-board electrical system battery and the output of the switched on electrical consumer to the ME-SFI [ME] control unit.
Idle regulation
- If the charge level of the on-board electrical system battery is high, (about 100%) the ME-SFI [ME] control unit does not increase the idle speed.
- If the charge level of the on-board electrical system battery is at a low level, the on-board electrical system battery is charged by an increased idle speed control. Adaptation takes place by means of idle speed control.
Regulation under engine load
- If the charge level of the on-board electrical system battery is at a high level then the on-board electrical system battery is permanently under no load.
- If the charge level of the on-board electrical system battery is at a center level, the driver-side SAM control unit requests loading of the on-board electrical system battery.
- If the charge level of the on-board electrical system battery is at a low level, the alternator is actuated by the driver-side SAM control unit.
Regulation reduces the engine loading, whereby less fuel is consumed and the exhaust emissions are reduced.
The alternator performs continuous self-diagnosis and sends the results via the drive LIN, driver-side SAM control unit and interior CAN to the ME-SFI [ME] control unit. The control unit compares the results with other signals (for example, engine rpm, on-board electrical system battery voltage, time since engine start) and thus detects any alternator faults.
The following faults are identified:
- Open circuit line for the bit synchronous drive-LIN interface or defect in interface driver of the driver-side SAM control unit
- Electrical and mechanical fault at the alternator:
- Control or diodes defective
- Stator interruption or short circuit
- Excitation interruption
- The charging voltage and charging current are not reached
- Charging voltage too high
- A cracked or loose poly-V belt
Diagnosis
A battery tester must be used to place a load on the on-board electrical system battery in order to check the charging voltage, since the charging voltage can be significantly reduced when the on-board electrical system battery is fully charged and under no load.
| Electrical function schematic for alternator interface | PE07.10-P-2709-97BBA | ||
| Overview of system components motor electronics (ME-SFI) fuel injection and ignition system | GF07.61-P-9997KJ |
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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.
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