- Check the tension and condition of the drive belt (see chapter Car maintenance). Replace a worn or worn belt.
- Make sure the mounting and adjusting bolts are tight.
- Inspect the cable and connectors of the generator and voltage regulator. They should be in good condition and tight.
- Check fuses.
- Start the engine and check for abnormal noises in the generator (chattering and squeaking indicate bearing wear, however, they may be due to belt slippage - see point a above).
- Check the density of the battery electrolyte. If it is low, charge the battery (does not apply to maintenance-free batteries).
- Make sure the battery is fully charged (one bad battery cell can cause excessive charging current).
- Disconnect battery wires (first negative, then positive). Inspect the battery terminals and wire lugs for corrosion. Clean them thoroughly if necessary (see chapter Car maintenance).
If your vehicle's radio is equipped with an anti-theft system, make sure you know the correct activation code before disconnecting the battery. Before disconnecting the wire, refer to Section Anti-theft audio system and instrument panel language.
If a message in a different language appears on the instrument panel display after connecting the battery, refer to Section Anti-theft audio system and instrument panel language.
2. When the ignition is off, connect a 12 V indicator lamp between the negative terminal of the battery and the tip of the disconnected negative wire. If the indicator lamp does not light up, connect the wire and follow the instructions of paragraph 4. If the indicator lamp lights up, there is a short circuit in the electrical system of the car (a leak). The short must be cleared before checking the charging system.
Permanent consumers should be disconnected before testing (such as clock or radio settings memory).
3. Disconnect the generator cable. If the control lamp does not go out, the generator is faulty. If the lamp continues to burn, remove the fuses one by one until the lamp goes out (it points to a component with a closure).
4. Check the battery voltage with a voltmeter with the engine off. It should be around 12V.
5. Start the engine and check the battery voltage again. It should now be around 14 to 15 volts.
6. Turn on the headlights. The voltage should drop and then rise again if the charging system is working.
7. If the voltage is higher than required by the charging system, replace the voltage regulator (refer to Section Replacing the voltage regulator). If the voltage is lower than required, then the diode (s) alternator, starter, or rotor may be faulty, or the voltage regulator may not be working properly.
8. If there is no short circuit that caused the battery to leak, and the battery is constantly discharging, then either the battery itself is faulty. Or the alternator belt is loose (see chapter Car maintenance), worn, lost contact or dirty alternator brushes (see Section Checking and replacing the generator brushes), voltage regulator not working properly (see Section Replacing the voltage regulator) or diodes, the stator winding or the rotor winding has failed.
9. Repair or replacement of diodes, stator windings or rotor windings is beyond the capabilities of a home workshop. Either replace the entire alternator or send it to an auto electrician who can repair it.
On models before 1986, if the charge/ignition lamp burns out, the battery stops charging. After 1987, a resistor was connected in parallel with the control lamp so that current would bypass the lamp if the circuit was broken (burned out control lamp).