Generator & Regulator Switch (Single Function Regulator)

1. Check for correct connections on fully charged battery, generator and starter motor. Check for good ground connection between engine and body. Check for properly tightened drive belt.
2. Connect DIS tester. Go to MEASUREMENT, CHECKING ALTERNATOR.
3. If charge indicator lamp is permanently lit, remove voltage regulator and check carbon brushes. If Bosch voltage regulator, see VOLTAGE REGULATOR (BOSCH)  under REMOVAL & INSTALLATION. If Valeo voltage regulator, see VOLTAGE REGULATOR (VALEO)  under REMOVAL & INSTALLATION. Minimum length of carbon brushes "A" is .20" (5 mm). See Fig 1 . Replace, if necessary.
4. If charge indicator lamp goes out while engine is running, check control voltage. Constant voltage regulation should be 14.3 volts. Regulator switch must be replaced if control voltage is not achieved. If Bosch voltage regulator, see VOLTAGE REGULATOR (BOSCH)  under REMOVAL & INSTALLATION. If Valeo voltage regulator, see VOLTAGE REGULATOR (VALEO)  under REMOVAL & INSTALLATION.

Fig 1: Identifying Brush Length

Courtesy of BMW OF NORTH AMERICA, INC.