Alternator voltage fluctuation
Thread Starter
Racer
Joined: Dec 2025
Posts: 360
Likes: 41
Alternator voltage fluctuation
Been chasing an intermittent voltage issue on my Z06. Alternator voltage drops to like 12.3 when idling (hot) but then generally jumps back into the 13's while driving? checked all connections and a couple tightened up a little...but didn't change anything overall . Alternator seems to test out fine (load test), so what should I look for next?
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,615
Likes: 4,061
From: Cape Coral, Florida
How exactly did you perform this alternator "load test" ??...normally for voltage issues like this we do a voltage drop check of the charging system from the battery to the alternator using a DMM...you must do a little more than "checking the connections"...they must be tested.
Last edited by C5 Diag; Yesterday at 01:24 PM.
Thread Starter
Racer
Joined: Dec 2025
Posts: 360
Likes: 41
How exactly did you perform this alternator "load test" ??...normally for voltage issues like this we do a voltage drop check of the charging system from the battery to the alternator using a DMM...you must do a little more than "checking the connections"...they must be tested.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,615
Likes: 4,061
From: Cape Coral, Florida
You may have to have some "skills" to diagnose this...with heat comes resistance and with resistance comes a voltage drop...voltage drop testing is easy and you should also be checking the alternator voltage AT the alternator...the B+ cable at the alternator goes to the starter solenoid and at the starter solenoid is the battery B+ cable...if the connection is poor there you will have a voltage drop...was that checked ??...you need to get under the car.
Last edited by C5 Diag; Yesterday at 02:21 PM.
Thread Starter
Racer
Joined: Dec 2025
Posts: 360
Likes: 41
You may have to have some "skills" to diagnose this...with heat comes resistance and with resistance comes a voltage drop...voltage drop testing is easy and you should also be checking the alternator voltage AT the alternator...the B+ cable at the alternator goes to the starter solenoid and at the starter solenoid is the battery B+ cable...if the connection is poor there you will have a voltage drop...was that checked ??...you need to get under the car.
https://youtu.be/vciL8qXVe2k?si=p7D033AKNFH7Fb4V
https://youtu.be/vciL8qXVe2k?si=p7D033AKNFH7Fb4V
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