Alternator interface function - GF07.10-P-1009OGA
ENGINE 642.8 in MODEL 207 as of 6/1/13, 212, 218 as of model year 2014
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 (N3/9) and the control response of the alternator is controlled. For this purpose, the CDI control unit reads in the following sensor and signal:
- Crankshaft Hall sensor (B70), engine speed
- On-board electrical system battery voltage (G1) via "circuit 30"
Function sequence for alternator interface
The CDI 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 CDI control unit controls the following functions:
- Switching on the alternator after engine start.
- Regulation of the alternator based on characteristics maps stored in the CDI control unit. To do this, the regulation voltage is preset by the CDI control unit.
- Protecting the alternator against overheating.
- Adapting the regulation voltage with a delay in the event of frequent load change at the alternator when idling to stabilize the idling speed.
- Generating a circuit 61 signal (alternator in operation).
- Sending detected faults from the CDI control unit over the chassis CAN 1 (CAN E1) front SAM control unit with fuse and relay module (N10/1). The front SAM control unit with fuse and relay module forwards the fault message over chassis CAN 2 (CAN E2) to the instrument cluster (A1).
The alternator constantly performs a self-diagnosis and sends the results when requested to the CDI 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 at output "circuit 61" of the CDI control unit.
Open circuit on alternator interface line (drive LIN) or interface driver fault in the CDI control unit. (For this fault, a regulation voltage of 13.45 to 14.15 V is specified.)
- 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 CDI control unit through the alternator interface, the "circuit 61 signal" is simulated in the CDI control unit and sent through an output stage connected to ground (e.g. for the instrument cluster).
| Electrical function schematic for alternator interface | Model 207 | PE07.10-P-2709-97EAJ | |
| Electrical function schematic for alternator interface | Model 212 | PE07.10-P-2709-97DAM | |
| Electrical function schematic for alternator interface | Model 218 | PE07.10-P-2709-97XAE | |
| Overview of system components for common rail diesel injection (CDI) | GF07.16-P-9997OG |