GF07.61-P-3003MIS ME-SFI Alternator Interface Function
GF07.61-P-3003MIS ME-SFI Alternator Interface Function
- as of model year 09
Function requirements for the alternator interface, general points
^ Circuit 87M ON (engine control ON)
^ Engine running
Alternator interface, general points
Through the alternator interface, messages are exchanged over the drive LIN (LIN C1) between the alternator (G2) and the ME-SFI [ME] control unit (N3/10), in order to regulate the alternator control response. For this purpose, the ME-SFI [ME] control unit reads the following sensor and signal:
- Crankshaft Hall sensor (B70), engine speed
- On-board electrical system battery voltage (G1) through "circuit 30"
Alternator interface function sequence
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 engine load, thus lowering the fuel consumption and improving the exhaust gas emissions.
The ME-SFI [ME] control unit controls the following functions:
- 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.
- Protecting the alternator against overheating.
- Generating of a "circuit 61 signal" (alternator in function).
- Reporting detected faults to the instrument cluster (A1) for actuation of the respective warning lamps 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 discontinuity at output "circuit 61" from ME-SFI [ME] control unit.
- Open circuit on alternator interface line (drive LIN) or interface driver fault in the ME-SFI [ME] control unit. For this type of fault, a regulation voltage of 13.45 up to 14.15 V is prescribed.
- Electrical and mechanical faults at alternator:
- controller or diodes defective
- stator interruption or short circuit
- excitation circuit open
- regulation voltage and charging current not reached
- regulation voltage too high
- cracked or loose poly-V belt
Diagnosis
To check the regulation voltage, the on-board electrical system battery must be loaded with a battery tester, as the regulation voltage can be significantly reduced when the on-board electrical system battery is under full or no load.
"Circuit 61 signal"
For alternators with an alternator interface, line "circuit 61" 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).
