A full-fledged electrical malfunction plagues your BMW when the alternator starts failing or goes bad. Even though your car may start, it will go off very soon. The headlights may become extremely dim. In serious cases of a bad alternator, the battery may get discharged and 'stone dead.'. An external battery tester (Midtronics EXP-1000) must be used to determine if the battery needs to be replaced. Energy Diagnosis will not prompt for a battery replacement unless the battery is “aged.” When energy diagnosis identifies the battery as “aged,” it means the amount of energy discharge over the course of the life of the battery scratch that, alternator was bad, just not bad enough to throw a code. Only charging at 12.7-12.8, should've been 13.5-14.0. Nearly killed the battery (was down around 12.0v when alt. was bad and measured from batt terminals,) maybe my experience chasing gremlins will help someone else. edit for clarity If yes- the alternator or voltage regulator is bad. The regulator I believe comes with a new alternator or can be replaced separately. If no- your reading shows a good 14+v at the alternator but 11.8v at the battery then you have a bad connection between the alternator output and the battery. BMW E90 328i Sedan / Repair Manuals and Technical Data / 61 General vehicle electrical system / 61 20 Battery / Closed-circuit current measurement Sporadically or continuously, an increased closed-circuit current can occur in the parked vehicle. If only fault codes 29F1/29F2 are stored in DME, refer to SI B12 16 06 (November 2006). SITUATION II. Customer may complain of: Excessive cranking time before engine starts (5-6 seconds) on cold start, or after hot soak, In most cases GT1/DIS diagnosis shows fault code 29DC, and/or 2FBF. It is an autophix 7910. I scanned my car after installing the new battery, water pump, and thermostat and pulled up a few codes. The ones that I pulled were : 1. 378F BSD, message (electric coolant pump): Missing 2. 3446 BSD, message (oil-condition sensor): Missing 3. 38A4 Intelligent battery sensor (IBS): communication fault The answer to your question is yes. Hard starting and rough idle are the hallmark symptoms of a bad eccentric shaft sensor. Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle. kB0U.