Torque Pro App vs Multi-meter for Volts

[mtbtim]

I just got an affordable multimeter from Amazon ($17) so I can have another tool to check my battery, charging system and whatever. Here's a link if you interested in the one I bought.
https://www.amazon.com/gp/product/B01DUH9VT0/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

This morning, I checked my battery after it's been sitting for 6 days. The volts were 12.5. I started the engine and used the multimeter and checked the charging system function at the battery posts. It showed it was charging at 14.3 volts. I checked what the Torque Pro app was showing at the same time, and it showed 13.3 volts. I finally used my OBD II reader and it showed 13.87 volts. I rechecked the battery voltage after shutting off the engine and the charging system boosted it up to 12.95 volts.

With todays testing and the values I got from O'Reilly's test machine, I'm thoroughly convinced the volts value the Torque Pro app is giving is not all that accurate. But, since I know it runs a little low, it can still be a useful tool to let me know something might be up with my charging system while I'm driving down the road.

 

[jeremyc74]

This morning, I checked my battery after it's been sitting for 6 days. The volts were 12.5. I started the engine and used the multimeter and checked the charging system function at the battery posts. It showed it was charging at 14.3 volts. I checked what the Torque Pro app was showing at the same time, and it showed 13.3 volts. I finally used my OBD II reader and it showed 13.87 volts. I rechecked the battery voltage after shutting off the engine and the charging system boosted it up to 12.95 volts.

.

It's odd that the Torque Pro app reads differently than the OBDII reader. With that being the case they must be doing something in the adaptor to measure voltage instead of pulling it out of the ECU, or they're pulling it out of the ECU and not interpreting it properly.

I'm starting to suspect that the voltage reading in the ECU is dumbed down like the reading on the temperature gauge, where it basically doesn't move until the temperature is outside of the normal operating range.

There's no good reason for the ECU to be seeing lower voltage than you're reading at the battery. Everyone keeps talking about voltage drop, but the drop would be a couple of hundredths of a volt at most on those runs. This makes me think that the ECU voltage reading that the OBDII (or Scan Gauge) is pulling was probably intended to drive a gauge in the instrument cluster that they decided not to put in, rather than being the actual voltage reading.

 

[TheDurk]

It's odd that the Torque Pro app reads differently than the OBDII reader. With that being the case they must be doing something in the adaptor to measure voltage instead of pulling it out of the ECU, or they're pulling it out of the ECU and not interpreting it properly.

I'm starting to suspect that the voltage reading in the ECU is dumbed down like the reading on the temperature gauge, where it basically doesn't move until the temperature is outside of the normal operating range.

There's no good reason for the ECU to be seeing lower voltage than you're reading at the battery. Everyone keeps talking about voltage drop, but the drop would be a couple of hundredths of a volt at most on those runs. This makes me think that the ECU voltage reading that the OBDII (or Scan Gauge) is pulling was probably intended to drive a gauge in the instrument cluster that they decided not to put in, rather than being the actual voltage reading.

I did a little research on the Torque forum and learned some things I did not know. Apparently the adapters do read the actual voltage at the OBDII socket, unlike other readings which are all digital. Torque will report this as well as the digital voltage reported by the ECM on different PIDs. The latter is labelled as 'Control Module' voltage. I can't check this myself as my battery is currently out while I do some work on the truck.

I have no idea which the ScanGuage units are reporting or whether they can do both. Likewise OBDII readers.

So this may account for some of the discrepancies. I still doubt the accuracy of the A-D/voltmeter function of the adapters even more than I doubt those of the ECM.

 

[mtbtim]

I did a little research on the Torque forum and learned some things I did not know. Apparently the adapters do read the actual voltage at the OBDII socket, unlike other readings which are all digital. Torque will report this as well as the digital voltage reported by the ECM on different PIDs. The latter is labelled as 'Control Module' voltage. I can't check this myself as my battery is currently out while I do some work on the truck.

I have no idea which the ScanGuage units are reporting or whether they can do both. Likewise OBDII readers.

So this may account for some of the discrepancies. I still doubt the accuracy of the A-D/voltmeter function of the adapters even more than I doubt those of the ECM.

The voltage sensor I'm using is labeled "Voltage (OBD Adapter)". There is another voltage sensor but it's not highlighted in green, so if I select it, I don't get any reading from it. When creating a new display with the Torque Pro app and I get to the point where I'm selecting what sensor I want, it says at the top "Add Sensor (Green = acti..." which I'm assuming means ones highlighted in green are active or activated.