Voltage Drop in Battery

JeffHicks · Post by **JeffHicks** » 27 Feb 2016, 22:24

'04 V70 T5

When I attach my scanner with the key off, the voltage reading is 12.4 - 12.7 volts.
When I turn the key on to the "run" position, the voltage immediately drops to 11.2-11.4 volts.

Is this unusual?
If it is "low voltage" how would the problems manifest themselves?

It doesn't seem to turn the engine over as fast as my '02 XC70 turns over. Could this contribute to some hard starts?

What are your thoughts?

Post by **precopster** » 27 Feb 2016, 23:45

Voltage measured at OBDII port with a scanner is often lower than battery voltage by as much as 0.8V measured with a DVM.

Yes the symptoms do look like the battery is weak after a voltage drop that's so great.

RavagedPheonix · Post by **RavagedPheonix** » 08 Mar 2016, 09:29

How old is the battery? That is a very significant drop in voltage. I would have the battery tested. If the battery tests good, I would assume its a wiring/corrosion issue. If you want to do some proper testing read this.

http://www.northernmobile.com/vdrop_two ... andout.pdf

This is a generic handout I give to my customers on how to test for voltage drops. You will need a basic voltmeter to do the tests. Read the first page so you understand what is going on and what you are testing for. READ THE FOOTNOTES. You will need to disable ignition or your fuel pump so the engine doesn't actually start during the tests. For your issue I would just do steps 1-8. Be aware these tests will drain your battery significantly and you will need to recharge it about halfway through the steps.