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Old 08-14-2009, 10:22 PM   #2
fdryer
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Join Date: Jan 2006
Location: NYC
Posts: 45,087
 

2003 L-Series 3.0L Sedan
Default Re: My battery is dead overnight

Look in the tach or speedometer - is the security light flashing? When you turn the ignition key to the ON/RUN position, does the security light turn OFF or stay ON? It must be OFF to allow the car to start and run otherwise if left ON and starting, the engine will not continue to run; the factory Passlock anti-theft system disables the fuel pump from running to stop the engine from ever running. Pulling the body control fuse somehow enabled the anti-theft system that must be reset first while attempting to find the cause of any short circuiting, if any exists. To reset the anti-theft system simply leave the ignition ON for 11-minutes or until the security light stops flashing. This time-out with the ignition ON and (not starting) allows resetting the anti-theft system. After the flashing stops, turn OFF the ignition and now try starting - with the ignition in the ON/RUN position this time, the security light should go OFF as the other panel lights turn off, leaving only the seat belt, oil, battery, and brake light/indicators ON. NOT seeing the security light at ignition ON will now allow starting and running. You can turn your attention to the original problem; possible battery drain.

Is the battery the original one or a replacement? If original, its likely overdue for replacement and may be the cause of your suspicion of battery draining. The body control module (BCM) runs everything the engine control module (ECM) doesn't. It draws very little current in standby mode when the engine is off. The ECM runs the engine, the bcm runs almost everything else; cruise control, the Passlock anti-theft system, remote key entry, all the lights in the car, and the OBD II system to determine and communicate to an external reader whatever ails the car. The bcm cannot be left disconnected as its part of the vehicle Passlock anti-theft system that communicates with the ecm and transmission control module as part of the anti-theft system to prevent stealing and using any of the three minicomputers. When you disconnected the fuse to the bcm you disconnected electronic communications that the bcm needs to stay in touch with the other computers - disrupting the anti-theft system communications automatically enables it and locks you out from having the engine running. The engine can start but will only run for a few seconds that the fuel pump primed the fuel lines before dying. Exactly as you described.

Either the battery needs a full charge or is in need of replacing. Be sure the battery cables are clean and free of any corrosion too. And be sure the belt tensioner is taut keeping the belt from slipping and allowing the alternator to supply the electrical needs of the car while charging the battery. The battery and alternator can be tested by most auto stores.
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