ME-SFI alternator interface function

Messages are exchanged between the ME-SFI [ME] control unit (N3/10) and alternator (G2) via the alternator interface which have the following tasks:

 Switching on the alternator after engine start.

 Regulation of the alternator according to performance maps stored in the ME-SFI [ME] control unit. To do this, the control voltage is preset by the ME-SFI [ME] control unit.

 Adapting the control voltage with a delay in the event of frequent load changes at the alternator to stabilize the idling speed.

 Protects the alternator against overheating.

 Generating a "terminal 61 signal" (alternator in function).

 Report detected faults to the instrument cluster (A1) for actuation of the respective warning lamps and display messages.

-----------------------------------------------------------------------------------------

The ME-SFI [ME] control unit actuates the control response of the alternator via the alternator interface, in order, for example, to decrease the charging voltage when idling when on-board electrical system battery is sufficiently charged (G1). The reduced engine loading means that less fuel is consumed and the exhaust gas emissions improved.

"Circuit 61 signal"

For alternators with an alternator interface line
"circuit 61" is not needed. From information which the ME-SFI [ME] control unit receives via the alternator interface, the "circuit 61 signal" is simulated in the ME-SFI [ME] control unit and is emitted via an output stage switching to ground (e.g. for the instrument cluster).

-----------------------------------------------------------------------------------------

The alternator constantly performs self-diagnosis and sends the results when requested to the ME-SFI [ME] control unit. The ME-SFI [ME] control unit compares the results with other signals (e.g. engine speed, battery voltage and time after engine start) and detects the following faults:

 Short circuit or discontinuity at output "terminal 61" from ME-SFI [ME] control unit.

 Line for alternator interface interrupted or interface driver in ME-SFI [ME] control unit defective. For this type of fault, a regulation voltage of 13.45 up to 14.15 V is given.

 Electrical and mechanical faults at alternator:
- controller or diodes defective
- stator interruption or short circuit
- exciter interruption
- regulation voltage and charging current not reached
- regulation voltage too high
- cracked or loose poly-V belt

 Diagnosis

In order to check the regulation voltage the on-board electrical system battery must be loaded using a battery testing device since the regulation voltage can be reduced significantly by a full and under no load on-board electrical system battery.