Testing Battery/Alternator Voltages - Multimeter or OBDII Code Reader???

Hello there,

I was using an Innova 3100 code reader to perform a test of the battery and alternator. The results of each test had a message attached to it saying that the voltage were below what they are supposed to be.

Battery Monitor Test: 11.20V (engine OFF)
Alternator Monitor Test: 12.55V (with all accessories on and running engine above 2000 RPM)

After getting these results, I hauled out my digital multimeter and performed the tests again. I then got the following results:

Battery: 12.4-12.5V (engine OFF)
Alternator: 13.6-14.0V (with all accessories on and running engine above 2000 RPM)

So my question is: which tool should I trust?

Cheers!

 

Did you use both at the same point where you plug into the OBII port.

They are both correct !!

The first is voltage drop going through the wiring and ecm to the port.

Second is most likely direct from battery terminals Correct ??

Myself I would rather use the Multi Meter more points for testing

 

Yes. I used the MM directly on the battery. Your explanation on voltage drop makes sense. Thanks!

 

Multimeter is more accurate. The ECM doesn't need to "know" the precise voltage for any of its normal functions, only for startup protection against a drained battery.

 

Makes sense. Nice to know that my battery and alternator are still good. Thanks!

 

While the multimeter is the best, my Scanguage II gives an exact match to the alternator output.

I'm not aware of any battery monitor testing available via the Scanguage. (someone educate me if there is)

 

With the way this electronic stuff changes I know I can`t keep up .

I mean really self driving cars