Quote:
Originally Posted by Buguyed
Do you think the voltage while driving will be much different them when just sitting at idle? What would I be looking for here?
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With the info you posted about your battery's voltage...I'd focus right now on getting multiple readings from your battery at rest & engine not running (with no surface charge) and then while the engine is running and you're driving around.
Do you know if you
are still using the original battery that came with the vehicle? If so, that may really point the finger at the battery being the culprit and it being on it's last dying legs. Even if the battery has been replaced...on average, it could be on it's 2nd battery...and at 9 years old...this wouldn't be out of line either since an automotive battery on general last from anywhere around 4 years to possibly 10 years depending on use & environment.
When you unlock your OBC...you should run TEST 9 before you start the engine or approx 2 hours after shutting down (this dissipates any surface charge)...then run TEST 9 while starting the engine and driving around. OBC TEST 9 shows you the battery's voltage (when engine is not running) and the alternator/charging system (when engine is running). This can give you an idea of where an electrical problem culprit may be.
The numbers you listed for engine not running & engine running are low. If the battery warning light hasn't illuminated (indicating an alternator/charging sytem problem)...then it could be a simple issue of your vehicle's battery giving you signs that it's about to fail.
A battery at
11.89 volts is at 0% state of charge and if still capable of starting the car...it's running on reserve capacity. You say that your battery was at 11.2 volts...and when voltage drops that low, odd electrical gremlins like warning lights illuminating but no symptoms can be found...are a common issue with many BMW models.
Again, unlock you OBC and do multiple TEST 9 samplings of the battery & alternator's voltage output (at rest & driving) and post back your findings. You should see some fluctuations at both rest & running...but for the most part, the battery should read above 12 volts...and the alternator should fluctuate between 12.5-13.8 volts consistently...depending on idle/load conditions.
Below is the procedure for unlocking the OBC (just like the link above) and there's also a brief description of the OBC TESTs. Disregard that it mentions "e38" in the heading...the "unlock" info applies to the e38/e39/e53 with the high instrument cluster...the low instrument cluster used in the e46 & e53 is similar except there's only 1 button on the cluster, so initiating the TESTs is slightly different as well as how they appear in the display since the low cluster doesn't have the larger 20-digit alpha/numeric display: