Hello all,

I’ve spent the better part of the past year getting my R53 Mini Cooper S drivable after some electrical and cooling issues. Got it all put back together this weekend and have taken it on a few drives - well worth all the work!

Dumb question though: Does OBD2 voltage reflect battery voltage? My scanner reads around 13.2 for OBD2 but doesn’t provide any battery voltage info.

One of my fixes was replacing the alternator and battery, and I want to make sure that it won’t die on me or leave me stranded somewhere.

Thanks in advance!

 

I'd like to know for 100% too.. I DO KNOW every time I've gotten voltage reading from the r53 obd2 ports they're NEVER accurate and are ALWAYS atleast 1.0v lower than what is read off the battery with voltmeter..I thought fir awhile I had voltage issues , even inpa reads it low when it's NOT LOW. I can read 14v at my battery , power wires ect but my my obd readings I've NEVER seen above 13.5v.
I was aaaaaand say the obd2 port reads the direct battery voltage but I can't say fir sure..
btw my gauge off my obd reads 11-13v.. when i had a failing/weak battery my 0bd port wouldnt even function unless it had full voltage to it.

 

I've always assumed that the voltage reported over OBDII was what the DME was reading. I see between 13.8 and 14 V over OBDII with the engine running.

 

Working at a Tier1 electronics supplier for many years, I would suspect that the reason the reported battery voltage via the OBD port is lower is that there is a diode (for reverse connection protection) somewhere along the path from the battery to the port. The voltage drop across the diode will cause a lower reading at the port than when using a voltmeter at the battery.

To confirm alternator output voltage, I would recommend to measure across the battery terminals with a voltmeter so that you know you are seeing the true reading that is reaching the battery when the engine is running.

 

I get the same reading as deepgrey on my Foxwell NT510 but my VDO gauge will show 14.2 while at idle and running under moderate load.

 

I have an Ultragauge plugged into my OBD II port....usually shows around 13.8v with engine running....I have a little voltmeter plugged into the lighter socket under the heater controls, it shows 14.2v at the same time with engine running

Bryan

 

The lighter socket likely only has a fuse in the path from the battery to the socket, so not a significant voltage drop to be had there (milliohms of resistance, maybe). At the OBD2 port, the protection diode could be in an ECU before the port, or the diagnostic tool itself may have the diode for protection. Makes sense.

 

Update: Picked up a multimeter and read the battery, it’s reading 13V resting and 14-15V running. Seems like all is well and the OBDII reading is a bit off. Good to know not to fully trust the OBDII reading. Thanks for the input!