In the VAST majority of cases, the only things that go wrong on alternators are the brushes wearing out (resulting in a weak magnetic field, this can be easily checked by placing a screwdriver against the alternator case) or the internal regulator/rectifier or diodes going bad. Unlike the 10-SI or 12-SI units, repair of the CS-series alternators by the layman is not nearly as simple as it used to be.

The diodes almost always short out or begin to “leak”, this is why many folks first notice battery drains, and in the morning the vehicle does not start. Avalanche diodes “collapse” and allow field current to continue to flow, thereby continuing the alternator’s output, instead of shutting down (losing forward bias) and starting up (overcoming forward bias thresholds) which creates surges and spikes. These diodes eventually leak and allow a path to ground, which eventually will drain the battery.