Voltage shows zero, no charge, but battery is good???😩

1997 xj. Driving to work the gauge dropped to zero (which is weird, normally with no charge it still shows source voltage). Limped it to work, shut down, restarted, gauge came back up and alt started charging.

What would cause gauge to drop to zero and kill the alternator?? Not trusting that it won’t do it again...

First question would be whether it's a charging problem or a gauge problem. All the other accessories and gauges working? I've seen a bad ignition switch or corroded fuses cause this too.

I would say charging issue, as lights went dim and I turned all accessories off to save my battery.

Weird thing is it charged next key cycle.

What I don’t understand is why the gauge showed zero even though battery was still holding 12.4V??

If the dashboard shows 9 volts typically there is an alternator issues, usually worn out brushes. If the dashboard gauge show 19 volts typically there is a connection or wiring issue.

If the brushes are worn, then can get stuck and the alternator will not charge. A bump in the road, removing the alternator for a Load Test, or stopping/restarting the engine is often enough to get the brushes unstuck and the alternator will charge normally.

Suspect / inspect the alternator brushes.

Thanks for the reply and advice. I would u e thought that IF you had an alternator failure the gauge would still show what the battery has in reserve (whether that’s 12v or less depending on how far you drive with no alt output).

Dickie, generally speaking I'd agree with you, the gauge should still read battery voltage, not 0. Problem is, on your 97, the gauge is driven via a CAN message from the ECM, not via some independent measurement of the battery voltage.

The ECM controls the dashboard display, and when it senses charging system faults it alters the dashboard display to advise the driver. Use your $6-15 volts/ohms multi-meter to check the alternator output and the battery charge resting voltage.

Let use know what the alternator brush inspection finds.