Denso suggests that when a vehicle is brought in with a charging system complaint to first check alternator performance.
If an alternator test bench is available, follow the procedures found on the bench tester’s instruction manual to conduct an alternator performance test. This test will determine if the alternator’s output is within performance specifications.
If the output is within specifications during the bench test, resolve problems in the remainder of the vehicle’s charging circuit and other electrical circuit that may affect charging circuit performance. Refer to the vehicle manufacturer’s service manual for the proper procedures to follow to identify and correct charging circuit problems.
If the bench test results show the alternator output is out of specification, replace it. Follow the vehicle manufacturer’s recommended procedure for inspecting the remainder of the charging circuit and other electrical circuits that may affect charging circuit performance.
If the alternator you are testing has an internal regulator, and the bench test identified the regulator as defective, it may be possible to replace the internal regulator and return the alternator to service. If the regulator is replaced and the alternator returned to service, follow the vehicle manufacturer’s recommended procedure to inspect the remainder of the charging system and other electrical circuits that may affect charging circuit performance.