why does my Volkswagen Passat B8 (2015-2022) battery light come on while driving?

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative terminal of the battery to avoid electrical shock.
• Ensure the vehicle is parked on a flat surface with the engine off and keys removed.

2. Inspect and Clean Battery Connections

• Sub-steps:
  1. Using a wrench, loosen the bolts on the battery terminals and remove the negative terminal first, followed by the positive terminal.
  2. Clean the terminals and battery posts with a wire brush to remove any corrosion.
  3. Reconnect the terminals, ensuring the positive terminal is connected first, followed by the negative terminal.
• Tools Required: Wrench, wire brush.

3. Test and Replace Battery (if necessary)

• Sub-steps:
  1. Reconnect the battery and test the voltage again with a multimeter.
  2. If the voltage is below 12.4 volts, consider replacing the battery.
  3. To replace, remove the battery hold-down bracket, lift the old battery out, and install the new battery in reverse order.
• Tools Required: Wrench, battery terminal cleaner.
• Parts Required: New battery (if needed).

4. Alternator Inspection and Replacement (if necessary)

• Sub-steps:
  1. Inspect the alternator for any visible damage or loose connections.
  2. Use a multimeter to measure the alternator output while the engine is running; if below 13.5 volts, the alternator may need replacement.
  3. To replace, remove the serpentine belt by releasing the tensioner, disconnect the electrical connector, and remove the mounting bolts to take out the alternator. Install the new alternator and reconnect everything.
• Tools Required: Socket set, serpentine belt tool.
• Parts Required: New alternator (if needed).

5. Check Serpentine Belt

• Sub-steps:
  1. Inspect the serpentine belt for any signs of wear, cracks, or fraying.
  2. If damaged, remove the old belt and install a new one by routing it according to the belt routing diagram.
• Tools Required: Serpentine belt tool or a ratchet.
• Parts Required: New serpentine belt (if needed).