2006 X5 M54 battery voltage discrepancy secret menu vs real measurement...

[cn90]

Car is 2006 X5 M54 with 133K miles, runs fine.

I just checked the battery voltage with engine OFF after a 1h trip.
Measurement roughly 30 min after the trip...

- Key in position I: "secret menu test 19, then function 9" says battery voltage = 12.1V, which is impossible bc this is after 1h trip.

- Opened the hood and measured using 2 separate voltmeters battery voltage = 12.6V, which is fully charged.

Has anyone here noticed this discrepancy before?

I trust my voltmeter more than the OBC of the E53...

[RocketyMan]

Originally Posted by cn90

Car is 2006 X5 M54 with 133K miles, runs fine.

I just checked the battery voltage with engine OFF after a 1h trip.
Measurement roughly 30 min after the trip...

- Key in position I: "secret menu test 19, then function 9" says battery voltage = 12.1V, which is impossible bc this is after 1h trip.

- Opened the hood and measured using 2 separate voltmeters battery voltage = 12.6V, which is fully charged.

Has anyone here noticed this discrepancy before?

I trust my voltmeter more than the OBC of the E53...

That's okay. The 12.1 is what the module sees. This is voltage drop--which is perfectly normal given the amount of wires before the module senses this.

[cn90]

Hmmm,

Thanks for the reply, does it drop that much 0.5V between the battery and the module(s)?

[Clavurion]

Originally Posted by cn90

Thanks for the reply, does it drop that much 0.5V between the battery and the module(s)?

I would still consider that normal. Usually the difference has been about 0,3 V on my E53 and E39.

[RocketyMan]

Originally Posted by cn90

Hmmm,

Thanks for the reply, does it drop that much 0.5V between the battery and the module(s)?

Oh yes--totally. Take a look at your battery in the back. The accessories go to a MJB with a mega fuse and then the smaller fuses. Then from that they splice off into which way. You have to consider the wire length as a whole in addition to each connection point. So the voltage-drop of 0.5 volts...sure. that's fine. It's above 12 volts that the module is sensing from it's own wiring. This is okay--and even more so when you confirmed at the battery you were getting your 12.6volts.

Most vehicle powernet designs take this into account--especially for the charging system. This is why ideally the voltage sense circuit is dedicated from the alternator directly to the battery post. That way the alternator can compensate for any losses in the lines to the battery for proper charging purposes.

[oldskewel]

Yes, I'd expect around 0.3. Would not be surprised at 0.5.

And if you use one of those cig lighter voltage gauge things, it will be similarly low, matching the cluster reading, below the measurement at the battery (which will equal the measurement at the engine bay jump port).

[andrewwynn]

Only God and the BMW engineer that programmed it knows where the voltage is sampled. It's a relatively thing. The absolute value isn't as important as what it is this week vs last year.

[wpoll]

0.5v drop matches what I see on mine too...

[bmw540san]

Yes, my experience as well and it seems to be normal.
OBC and my AutoEnginuity scan tool show 0.5V and sometime even whole 1V less than my trusty Fluke digital Voltemeter.
Like others said, it depends at point of measurements and on some other factors.
But my 97 528 with low OBC always shows correct, around 12.6 and 14.1 when engine running, go figure.