Tech Tips (by ALLDATA): Easy fix for a hot Nissan alternator
Vehicle: 2004 Nissan Altima, L4-2.5L (QR25DE)
Problem: This Altima originally came into the shop because the battery light was ON. The technician diagnosed the problem as a bad alternator and replaced it. When he started the engine to test the charging system, the new alternator quickly became very hot. He replaced the alternator again assuming the first one was defective. The second alternator did the same thing (A hand-held digital temperature sensor read 190°F).
Details: A call to ALLDATA Tech-Assist provided some good insight. The consultant advised the tech that is was possible that one alternator could have been bad but the same overheating problem with two alternators was not likely. He suggested checking the resistance between the alternator housing/case and the negative battery post. If it was high, the tech needed to check the engine ground cables.
The technician found that there was high resistance to ground at the alternator case. A closer inspection revealed a corroded ground cable on the engine block.
Confirmed Repair: The tech cleaned and reinstalled the engine ground cable. After that repair, the resistance to ground at the alternator was acceptable and the alternator no longer ran hot. Cleaning the ground cable resolved the problem. Fixed!