Alternator Control, Basic Function - GF15.40-P-1058A

Engine all (CAR) 

Overview 

This document contains information on:

• General 
• Function requirements 
• Function 

General 

To optimally control the charging voltage of the alternator, the alternator and the combustion engine control unit exchange data via the alternator control function. The alternator control function makes the exchanged data plausible and corrects it depending on the vehicle's operating state. In addition, the alternator control function records mechanical or electrical faults in the alternator.

Function requirements 

• Engine management ON (circuit 87M)
• Engine in operation

Function 

Alternator control function 

The alternator control function requests the optimized charging voltage from the alternator. The optimized charging voltage is calculated from the following information:

• Specified voltage of the alternator management
• Corrections by output management

  In order to calculate the optimized charging voltage for the alternator, the following processes take place:

  Reading out the operating rate of the alternator 

  In order to control the power output of the alternator, the combustion engine control unit assesses the operating rate of the alternator. To this end, it uses the data transmitted by the alternator.

  Calculating the specified voltage of the alternator In order to determine the specified voltage of the alternator, the body/drivetrain central control unit uses the operating rate of the alternator. This involves the alternator control function.

  Optimizing the specified voltage of the alternator 

  In order to record the on-board electrical system voltage, the following information is read in and compared:

• The calculated specified voltage of the alternator
• The actual value of the alternator voltage

In order to compensate for fluctuations in the on-board electrical system voltage in certain vehicle operating states, the output management optimizes the specified voltage at engine start, for example. This results in the optimized charging voltage.

Alternator self-diagnosis 

The alternator performs self-diagnosis continuously. On request, it provides its status as a signal.

The alternator control function detects the following electrical or mechanical faults:

• Line of the alternator control function has an open circuit
• Control or diodes defective
• Interruption or short circuit in the stator
• Excitation interruption
• Charging voltage too low or too high
• Cracked poly-V-belt
• Poly-V belt tension too low or too high

	Function schematics
	Function schematic for alternator interface	ENGINE 260, 282, 608 in MODEL 118, 177, 247   ENGINE 264 in MODEL 167	PE07.10-P-2504-97A
		ENGINE 176, 177 in MODEL 167	PE07.10-P-2504-97B
		ENGINE 139 in MODEL 118, 177, 247	PE07.10-P-2504-97C
		ENGINE 256 in MODEL 238 as of MODEL year 2021   ENGINE 256, 264 in MODEL 213 as of MODEL year 2021   ENGINE 654 in MODEL 118, 167, 177, 247   ENGINE 654 in MODEL 213, 238, 257 as of MODEL year 2021   ENGINE 656 in MODEL 167	PE07.10-P-2504-97D
		ENGINE 279 in MODEL 223	PE07.10-P-2504-97G
		ENGINE 656 in MODEL 223	PE07.10-P-2504-97H
	Control units
	Combustion engine control unit, basic function	ENGINE all (CAR)	GF07.08-P-9890A