If one or more diode fails the ripple becomes excessive. This can cause charging issues or stress other electronic components in the vehicle. The alaternator may still work but it is not working well.

What does excessive ripple mean on an alternator test?

Excessive ripple voltage can cause communication issues with networks and communication DTCs in multiple modules. ... Before computers and networks in vehicles, an alternator that was producing AC voltage or ripple through the electrical system would cause flickering lights and maybe an ignition problem.

What does ripple mean in alternator?

Rabble-Rousing Ripple

Diodes rectify the stator's AC current into DC. Although this happens, a small AC voltage still appears at the alternator's output terminal. When properly displayed on a scope screen, this AC voltage has a rippled appearance; consequently, it's called alternator ripple.