Alternator interface function - GF07.10-P-1009MI
ENGINE 272.9 (except 272.982) in MODEL 204.0/2 as of model year 2009
ENGINE 272.9 (except 272.983) in MODEL 212
ENGINE 272.9 (except 272.984) in MODEL 207
ENGINE 272.9 in MODEL 204.9
ENGINE 273.9 in MODEL 207, 212
Function requirements for the alternator interface, general points
- Circuit 87M ON (engine timing ON)
- Engine running
Alternator interface, general points
Using the alternator interface, messages are exchanged via the drive train LIN (LIN C1) between the alternator (G2) and the CDI control unit (N3/10) and the control response of the alternator is controlled. The ME-SFI [ME] control unit reads in the following sensor and signals for this purpose:
- crankshaft Hall sensor (B70), engine speed
- on-board electrical system battery voltage (G1) via "circuit 30"
- alternator, status and circuit 61 via the drive train LIN
Function sequence for alternator interface
The ME-SFI [ME] control unit controls the alternator control response, for example, in order to reduce the regulation voltage (charging voltage) when the engine is at idle and the on-board electrical system battery is sufficiently charged
This reduces the engine load, thus also reducing fuel consumption and improving exhaust emissions.
The ME-SFI [ME] control unit controls the following functions:
- switching on the alternator after engine start.
- regulation of the alternator according to characteristics maps stored in the ME-SFI [ME] control unit. To do this, the regulation voltage is preset by the ME-SFI [ME] control unit.
- adapting the regulation voltage with a delay in the event of frequent load change at the alternator when idling to stabilize the idling speed.
- protecting the alternator against overheating.
- generating a circuit 61 signal (alternator in operation).
- recognized faults via the chassis CAN (CAN E) to the instrument cluster (A1) for actuation of the respective warning lamp and display messages.
The alternator performs continuous self-diagnosis and sends the results when requested 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:
- short circuit or open circuit on output "circuit 61" of the ME-SFI [ME] control unit
- line for alternator interface (drive train LIN) is interrupted or interface driver in ME-SFI [ME] control unit defective (A regulation voltage of 13.45 to 14.15 V is prescribed for this fault).
- electrical and mechanical fault at the alternator:
- control or diodes defective
- stator interruption or short circuit
- excitation interruption
- regulation voltage and charging current not achieved
- regulation voltage too high
- a cracked or loose poly-V belt
Diagnosis
To check the regulation voltage, a battery tester must be used to place a load on the on-board electrical system battery, as the regulation voltage can be significantly reduced when the on-board electrical system battery is fully charged and under no load.
Circuit 61 signal
For alternators with an alternator interface the "circuit 61" line is not needed. Using the information received by the ME-SFI [ME] control unit through the alternator interface, the "circuit 61 signal" is simulated in the ME-SFI [ME] control unit and sent through an output stage connected to ground (e.g. for the instrument cluster).
| Electrical function schematic for alternator interface | MODEL 204 | PE07.10-P-2709-97FAB | |
| MODEL 207 | PE07.10-P-2709-97EAB | ||
| MODEL 212 | PE07.10-P-2709-97DAB | ||
| Overview of system components motor electronics (ME-SFI) fuel injection and ignition system | GF07.61-P-9997MI |