2001 Honda Civic, with probably bad alternator. With the engine running, I disconnected the output wire, confirmed 12 volts at the end of the disconnected alternator wire (from the manually charged battery), and read only 1.8 volts on the alternator output terminal with the engine at idle. With the engine running faster, alternator output voltage rose to about 5 volts. Before I replace the alternator, is there any chance this could be some sort of alternator regulation issue? If so, how can I check that?

. Use a voltmeter to check battery voltage with the engine off--it should be approximately 12 to 12.35 volts.

. Start engine and check battery voltage again--it should now be approximately 14 to 15 volts. Check the 15 ampere ACG (ALT) (S) Fuse, in the under hood fuse box, and the 80 ampere Power Distribution Fuse, in the under hood fuse box, with a test light or multimeter if the voltage reading is less than the specified charging voltage. If either fuse is blown, replace them. If the fuses are good, replace the voltage regulator and brush holder assembly; otherwise, install a new alternator.

Rebuilding alternators is fun. If you decide to go that route, this link may give you inspiration:

https://www.askmehelpdesk.com/cars-t...tml#post666293