My AutoXray scanner seems to show somewhat lower voltage than expected from my Z28. So I figured I'd ask others here who may have one what sort of voltage ranges theirs show while the car is running.

Mine for example will only show a max of about 13.9v after a cold start up, 13.1-13.4 or so driving, and can fall to a scary 11.9 at idle in gear if you stop at night with the lights and a/c on. (looks like potential trouble there, the dash volt meter almost touches the red at that point)

So anyone who can answer for me I'd appreciate it. I just don't want to start hunting a possible charging or wiring issue to find out the scanners just read a little low.

 

My voltage is around 12, practically red lining whenever in idle. Upon startup its a lot higher. I am running a lot of audio equipment though. I'd imagine the scanner to be pretty accurate. Like you said your dash panel is confirming the low voltage. You could get a higher amp alternator if you're really concerned but I think you're alright, but then again im not expert.

 

The scanner is reading system voltage from the PCM. Based on reviewing numerous scans, and simultaneously using my ScanMaster reading the PCM, a laptop reading my MoTeC ECU and watching the dash gauge, there does not seem to be a direct correlation between the voltage the PCM/ECU sees and the volt meter on the dash. Generally, my ScanMaster shows a lower voltage than the dash gauge. Might have something to do with the points at which each device is connected to the system. The dash gauge may go directly to the alternator, while the PCM is fed through a longer path, including fuses.

I would think if you are seeing low volts on the AutoXray, and low volts on the dash gauge, you either have a weak alternator or some heavy loads on the system.

 

The gauge and the scanner should generally show the same voltage. They both receive power through the ignition switch (which IMO seems to be a source of voltage drop after on for a little while).

Put a volt meter across your battery and compare that to what the Autoxray says. I bet it is almost a volt higher. I find it typical to see lower hot voltages on the gauge and scanner than what is seen at the battery.

 

I've done that. They generally seem to be about 1.5 volts apart on my Z. Haven't checked on other cars. Once I verrified my dash gauge was right and the Auto Xray was wrong. I didn't worry about it any more.

 

Before I read the replies on here I did do a quick check with my volt meter at the battery on a cold start. The autoxray read about 13.5, my volt meter 14.4v.

I'll gather some more info in different conditions tonight. As far as loads go, the only non original electrical items on the car are the opti, plugs and wires, MAP sensor, some of the tail light bulbs, one of the fog lamp bulbs, the starter, fuel pump, and a Valentine One radar detector. Everything else is original down to the 3 speaker Bose CD.

The reason I'm looking into this is it runs a little rough at idle. Seemingly more so with higher electrical load. Daytime it's not so bad, but if it's at night with lights on and even running the A/C compressor, it's worse. Give it a little gas and it's happy again. At night at idle the dash lights will flicker a bit.

 

Cold start 900rpm in park, headlights on:
AutoXray: 13.7v
Voltmeter: 14.5v

Warmed to 750rpm in park, headlights on:
AutoXray: 13.3v
Voltmeter: 14.2v

Warm 550 in drive, headlights on, A/C on:
AutoXray: 12.1v
Voltmeter: 13.2v

Warm 650 in park, headlights on, A/C on:
AutoXray: 12.8v
Voltmeter: 13.9v

So the actual battery voltages seem safe. Suggestions as to where to go from here would be appreciated.

 

Sounds like your alternator is on it's way out. My AutoXray always reads the same as the gauge on the dash.