Ok, I have a pretty cheap device I plug in at times, it reads codes etc, I use it with a couple different apps. Torque Lite, and free version of Car Scanner ELM. My son also uses Piston, another app.
It does read codes and resets as needed. And it does seem pretty accurate with one car, an older Miata.

My issue, which I discovered today- I have an older Chevy Silverado. Yes, in the app, I have gone in and specified that exact model, and it will read codes and sensors, and what-not. BUT:
it reads my voltage as 11.8 while not running, and around 13.3 running. This is with any of the different apps, not just one. Those numbers are LOW. And I just recently replaced both my alternator and battery (due to physical symptoms, not because of the app reading).

Took it to Autozone, and THEY checked it. With their scanner, with a voltmeter, and they checked the system.
Everything passed. Battery was 12.8v, running my alternator output was over 14v and charging the battery. When they did the scan and plugged it back into their computer, it matched their numbers, not my OBD2 readings.

Trying to figure out why. I know, it's a cheap dongle, not a $400 tool. But I'd think if there was an issue, it simply wouldn't read, and not give a false reading. And the apps do connect, they do give a lot of info, I can read codes, I have reset them using it, it appears to be functioning properly in that regard. When driving, it does give me correct speed, correct RPM etc. At first I wondered if my car computer might be the issue, or the OBD port... but their scanner connected and gave correct reading. So I don't think it's those, because it would be giving the incorrect reading on their scanner too.

Is there a way to calibrate these things?

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Posted by LEASTBAY

Member since Aug 2007

16443 posts

Posted on 7/16/25 at 10:48 am to Scoob

I always assumed the vehicle computer comes up with the numbers. It just sends it through the port.

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Posted by Scoob

Near Exxon

Member since Jun 2009

23154 posts

Posted on 7/16/25 at 11:34 am to LEASTBAY

quote:
I always assumed the vehicle computer comes up with the numbers. It just sends it through the port.

Yeah, that's the thing. I've used this to read and clear codes in the past, it reads sensors and gives me live data. As I state, it matches my RPM and speed, and presumably temps and other sensors. And I've double-checked, I AM using the correct profile for the truck in the app.

It's just giving me low voltage numbers. First, he checked the alternator, battery and starter with a device that hooks to the battery terminals. That gave the different, "correct" numbers showing battery about a volt higher, and running the voltage over 14. Which btw is matching what my dash voltmeter says, about 14.3 or maybe higher, it's an analog dial.
Noting the difference, he went and got a voltmeter, and again over 14 running.

At that point I wondered if my ECU was failing or off, so he did the OBD scan with their scanner. Again, correct "good" numbers, basically 1 volt higher than what my apps say. I've used 3 different apps, the numbers match on those...
I don't get it. I would think the numbers are, like you said, put out by the ECU in the car. The dongle would either read, -- or it wouldn't. It shouldn't give a false number.
It shouldn't give a different number than their scanner, hooked to the same port.

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