2012 Toyota Highlander Auto V6 with 3.5L(2gr-fe), 162k miles. Warning light for charging came on, just replaced battery 300 miles ago. Parts store said alternator checked ok. (Possible intermittent issue). Next morning, voltage on resting battery was 12.7V. With engine running and no electrical accessories, Voltage started at 14+V, then within 1 min dropped to 12.7. With accessories on, dropped to 12.0V. Checked continuity from Engine block to Neg Battery post, passed. Positive Battery post to alternator connecting wire, passed. Neg battery post to casing of Alternator, failed. Comparison with Rav4 with same engine, 2gr-fe, passed continuity from Neg battery post to casing of alternator. Revving engine does NOT brighten high beam lights. Is it clearly a bad alternator or bad connection in losing ground? Are there steps to removing alternator without taking the fan shroud off and draining coolant? I'm not sure where to look for wiring diagram to check if there is an issue with wiring. As it stands now, belt off, 2 bolts out, back bracket bolt out, 1 electrical connector off, positive cable off. It ain't moving.
Belt tension on Highlander was similar to belt tension on Rav4 with same engine. Alternator pulley spins freely.
Is it a bad alternator?
Checked continuity from Engine block to Neg Battery post,
continuity test is not a reliable test. It will pass even if the ground strap is hanging on by a thread, but that's not good enough. You need to measure the voltage drop under high load.
Well you said the ground test failed. I would reground it and go from there. But if that doesn't fix it then yeah? Unless the car's been wrecked and the wiring's been damaged. I'd say it's a bad alternator and they are kind of a pain to replace. But it can be done with normal tools if your patient and do it on a cold engine so you don't burn yourself
I had the same issue happen about 3 months ago with my 2009 Highlander and had the alternator replaced. It works great now!
With accessories on, dropped to 12.0V
one of the accessories might have a short