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what do it mean.when you do a charging system test,and the result, say a excessive rippleing.

A sophisticated charging system check will include checks for bad diodes. When the diodes fail or start to fail you will commonly see excessive ripple voltage in the circuit. Some other problems are rectifier spikes and noise. Ripple voltage can cause problems with the vehicle’s ECM or PCM due to the unsteady or undulating voltage (rippling) from the alternator. In other words, your alternator is failing.

Missleman is correct. There is too much alternating current voltage on the direct current bus. Besides a failing alternator, a high resistance connection to the battery or a battery close to the end of its life can cause this high ripple. A load test of the alternator would clear or condemn the alternator.

Alternators produce 3 phase alternating current. A “Diode trio” converts this A/C to DC. When one of the diodes gets weak or fails, some of that A/C current shows up on the output terminal as “ripple” . Computers do not like A/C ripple. In some cars, the dashboard lights up like a berserk pinball machine…The AM band on your radio will be very noisy with the A/C whine from the defective alternator…