Manual Test Of Alternator Function
- Start the engine and allow it to idle for approx. 1 minute.
- Make sure that no extra electrical consumers are connected. Turn off functions that consume a great deal of power, such as the ventilation fan, heated rear window/door mirrors, heated seats, lighting, radio system, etc.
Values for battery temperature and voltage are read and displayed continually during the test. Select values that are available in the list window. Wait approx. 5 seconds between each battery temperature change to allow the alternator to have time to set the right voltage in relation to the set battery temperature. Then read battery temperature and voltage between each temperature selection.
Compare the values from the readout of battery temperature and voltage with the values in the table.
Battery temperature (T) (°C) Voltage (U),
lower limit (V)Voltage (U),
upper limit (V)+60°C, +70°C, +80°C, +90°C 12.80 V 13.60 V +50°C 12.95 V 13.75 V +40°C 13.27 V 14.07 V +30°C 13.58 V 14.38 V +20°C 13.89 V 14.69 V -30°C, -20°C, -10°C, 0°C, +10°C 14.20 V 15.00 V If the voltage values generally lie below the lower limit (low voltage), redo the test at an engine speed of 2500 RPM.
If the voltage is within the tolerances this time, alternator function is OK, but the test indicates that the battery is not fully charged. If voltage still deviates, there is a fault in the charging system.
NOTE: The read-out voltage is read internally from the central electronic module (CEM) and deviates slightly from the actual alternator output voltage due to a drop in voltage in the wiring harness.