1990 Cadillac Battery Goes Dead Overnight and Won’t Start

1990 Cadillac Fleetwood. The car won’t start due to dead battery after about 12 hours. I have had the battery and alternator tested, and they tested OK. There must be a power draw somewhere. Do you have any ideas? The battery and alternator tested OK.

Mechanic JK:
By what you are describing, it sounds like you may have something that is called a ‘parasitic draw’. This is a current and voltage draw on the battery with everything turned off. That is assuming nothing has been left on by accident, like a dome light, or something plugged into the cigar lighter outlet. Be sure to check these basic things before going any further. Also disconnect any non-factory electrical items you may have, like an alarm, remote starter, radio or amplifier.

The way to diagnose this problem is to have a mechanic hook up volt/ohm meter to the negative battery cable. With everything off, check for a draw on the battery by putting the meter on the Amp scale and have one meter terminal on the battery, the other on the cable. If there is a draw, you will see it on the meter. A rule of thumb is that 50 Milliamps is the limit. This can be read as .050 on some meters. If your Cadillac has more than this, start removing fuse one at a time until the draw goes away, or to at least acceptable levels.

Any number of computers or modules in the car can cause your battery drain problem. Most draws will drain a battery overnight, some more severe will take only a few hours. Some common areas on this vehicle to check would be the glove box light staying on, visor or vanity mirror lights stuck on, a power door lock or window switch contacts sticking, trunk light staying on or an internal draw in the radio ETC. These are some things that you can check if you like before taking it to a technician.

1993 Cadillac

My dad has a 1993 Cadillac, cranks great and runs great when cold start, after 7-8 minutes when car warms, just quits, no stuttering or sputtering, just dies til cool again, already replaced control module and ignition coil, bout to lose my mind, cant keep paying shop to put things on with no luck or keep paying to have checked, just an old man on ss, have any ideas?

Usually a problem like that is hard to diagnose, but most times it does have to do with either the ignition module or crank sensor. Those are the two things most affected by the heat of the engine, which usually takes 5-10 minutes to make it die out. If you can I’d recommend getting it scanned for any trouble codes, and possibly using the scanner to watch the live data stream as you drive it to see what sensor is falling off and causing it to die out. Could be almost anything really.