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Mike S.
Mike S., ASE Certified Technician
Category: Cadillac
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Experience:  ASE certified
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1998 Cadillac Deville: the alternator..battery cables..disconnected

Customer Question

I have a 1998 Cadillac Deville. The battery keeps dying. I have replaced the alternator, battery, battery cables, battery posts, and disconnected the aftermarket stereo. It still dies... I checked all of the fuses, even the ones in the trunk... still dies after about 12 hours. so, i checked out this post:

Re: 1998 Deville, weird electrical problem
You are on the right track with the BCM(PZM), on the Deville if a Aftermarket radio is installed without installing the original in the trunk it causes all kinds of weird things to happen. The problem is it is very random and will drive you nuts trying to correct. Your model Deville has a deep sleep mode which is controlled by the bcm, it also has a battery saver mode as well, both of these could be combining to produce this loss of memory etc. If you do a search there is a link that is entitled for those who own a 97-99 Deville in the audio section, it covers what is happening to you and how to fix it. My BCM did the exact same thing on my Deville as yours is doing.
just came back to say what he said, figured it out, here is some more info
all u ahve to do is run the two databus (i believe purple) wires to the trunk and find power and groundings in the trunk or 4 wires if u want chime. two databus and two speaker wires to the trunk... here is a posting i copied.

OK, after sifting through this thread I started getting angry at all the mis information. I went through this all durring the summer. I replaced the stock unit and all the speakers. The "sleep mode" you are expirenceing is because the stock unit has to remain wired in the car or the car is going to go into lockdown mode. You dont need any fancey harness, just the standard harnesses, and a spool of wire. The stock stereo is going to have to be relocated to the trunk. I put mine next to the wheel well. You will have to run power, ground and the databus wires to it, and a speaker if you want chimes. the data bus wires are pins F6 and E6 on the harness. Ground the unit on the body and run the power wire from the 12gauge wire coming from the radio fuse in the fusebox located in the trunk. As for the aftermarket unit. The stock wireing is not a constant 12v and there is no accessory wire. for the 12v I ran a wire to the fuse box in the trunk to one of the thicker 10gauge wires. You will need to test this with a multimeter to make sure its alwasy 12v, even when the car is off. The accesory wire i ran into the power window circuit (blue 12 gauge wire). This is optimal because its close and it retains power after the car is off untill the door is opend or 10min. This is just a quick overview. If you have any question or would like me to go more in depth, PLEASE PM ME, I will be very happy to help you. (Note: I spent a good 12 hours on this my first time, Its not to difficult, but time consuming)

after reading this post, I reinstalled the factory stereo. same issue. please help...
Submitted: 5 years ago.
Category: Cadillac
Expert:  Mike S. replied 5 years ago.

It sounds to me as though something is draining the battery over time. It's a short and it's like something being on when it is supposed to be off.

Test for a drain on the battery by a using a 12-volt test light or voltmeter. Take a full reading across the battery posts to get total battery voltage. Write that down. Then disconnect the negative battery terminal and hook the 12-volt test or voltmeter with the positive test lead on the disconnected negative battery cable and negative test lead on negative battery post. Turn everything off, close the doors and if you have a hood light remove the bulb.
With the negative battery terminal disconnected and a test light or voltmeter between the cable and post see if you have a drain showing on your test light or voltmeter. A light on the 12-volt test light or voltage reading on the voltmeter indicates that something is draining the battery. If so start by unhooking the small wires at the alternator and see if the test light goes out or dimmer or if the voltmeter drops in voltage, hopefully to zero. If the 12-volt test light goes out or the voltmeter now reads zero or less than 0.2 volts then you have found the short. If the voltage is not zero on voltmeter or test light does not go out, the short is somewhere else. If the voltmeter just drops some or the 12-volt test light just dims a little you still have a you have a drain there but still a drain somewhere else so start pulling the fuses 1 at a time and when you do find out when you pull a fuse and the drain gets lower then put the fuse back in hook up the battery and make sure everything on that circuit works. Let me know which fuse you pulled and I’ll upload the wiring diagram so you can check everything on that circuit and make sure that it works. If something doesn’t work on the circuit that is causing the drain then it may be short-circuited with another circuit of shorted to ground. That may help find where the short is if something don't work. So with your 12-volt test light or voltmeter test the wiring to whatever doesn’t work to find out where it has voltage and all of a sudden looses voltage and then repair that spot. If any drop some or allot write it down which fuse it was and if using a voltmeter write down how much volts it dropped. Remember if you have to keep the door open to pull the fuses just push in on the door switch after every time you pull a fuse and go to look at the meter. When all fuses are pulled and the alternator wires are off you should have no drain and written down everything that was causing a drain. If you still have a drain with every fuse pulled and the alternator wires off, then it must be something that is unfused such as anything that may be fed from the light switch.
Last if you have all the fuses out and still have a drain disconnect the big wire at the alternator. If the drain now goes away you have a bad diode in alternator.

When you find out which fuse it is and what circuit or circuits are causing the drain, let me know and I'll upload the wiring diagram.

Customer: replied 5 years ago.
I tried all of that except for the last part about the bad diode because its a new alternator and the old one turned out to be good as well. There was not any flutuation when i checked each fuse. the only flutuation i got was when a disconnect the big power wire from the fuse panels...the one under the air filter box. any other ideas? what is this sleepmode controlled by the bcm?
Expert:  Mike S. replied 5 years ago.

When you hooked up the 12 volt test light or voltmeter did it show a drain? If so was you using a voltmeter or test light? When you pulled fuses did you leave them out untill you had them all pulled? Did you pull all the fuses out of all the fuse boxes,blocks?

Expert:  Mike S. replied 5 years ago.

There are 3 fuse blocks.


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Customer: replied 5 years ago.
Volt meter did not show a drain.... I pulled each fuse out one at a time... I put the fuse back in if it did not drop. I used one that has 00.00 reading.
Customer: replied 5 years ago.
Please respond to the last statement... I hit the wrong button;)
Expert:  Mike S. replied 5 years ago.

Sorry, I was napping.

If the voltmeter wasn't showing a drain, there was no use in pulling all the fuses. Are you sure you hooked up the voltmeter correctly? The negative test lead toward the negative battery terminal. What scale did you have the voltmeter on?