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      10-01-2015, 05:24 PM   #5
401FlaGATOR
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Drives: E90 325i ZSP, F30 320i ZSP
Join Date: Oct 2006
Location: Pembroke Pines, FL

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I had a similar problem with my E90, suspected the battery but it ended up being the starter..It could also be another issue like fuel pump. The best way to diagnose is to eliminate the possibilities starting with the battery, you can check your battery with a low cost volt meter to see what the volts are when the car is off. A battery that has been sitting all night will still show 12.x in the morning..12.25 to 12.5 at 75 degrees F is a good indicator in most circumstances. Measure at the battery terminals..I have found discrepancies from the OBD due to voltage drop I think. You can take another reading with the car on..Voltage would be around 13.5, 13.75 V, or higher..

In a minority of cases the two checks above can look ok but the battery can still not have enough high current capacity to start the motor, you would need a load tester to check that which is more expensive. However in my experience the checks with the voltmeter are about 95% definitive.

Usually when your battery cannot turn on the car it will not be able to start it on subsequent attempts. This is just physics, if it doesn't contain enough energy to do it the first time it will have even less on the subsequent attempts. If it routinely starts on the subsequent attempt there is less probability that the battery is bad and more probability that you have a problem elsewhere.

You could forego the voltmeter initially and just use OBD scanner or secret menu to get a quick idea of your battery voltage. A voltage of 11.9 or lower is a red flag that your battery or alternator is defective.