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Discussion Starter #1
Many times, when I unlock the door with the key, then turn the key in the ignition, the security alarm goes off. If I get out and "unlock" the door again, though it's already unlocked, the alarm quits.

This is happening more and more; three times in a row today.

Where to start looking? I've had intermittent electrical glitches for years: the rear windshield wiper turning on by itself, door locks unlocking when I'm away from the vehicle, etc.

Is it time for a complete BCM replacement? If so, where to find reconditioned BCMs (they seem to be scarce), and reliable installation instructions?

Maybe relevant: I have a "lift door zone switch error" when scanning body codes, but haven't been able to find what a lift door zone switch is by Google search.

This is a 1996 Grand Caravan LE, 3.8L

Thanks.
 

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Discussion Starter #3
Helpful video, but he doesn't go into much detail.

For example, will the reading on the multimeter read only the AC ripple?
Do you connect the meter across the battery terminals?

Also, is it possible to fix excessive ripple by adding another diode external to the alternator?
If so, what type?

Are there other factors inside the alternator like built-in capacitors that have to be taken into account if you're adding an external diode?
 

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Alternator test and fix ideas

Helpful video, but he doesn't go into much detail.

For example, will the reading on the multimeter read only the AC ripple?
Do you connect the meter across the battery terminals?

Also, is it possible to fix excessive ripple by adding another diode external to the alternator?
If so, what type?

Are there other factors inside the alternator like built-in capacitors that have to be taken into account if you're adding an external diode?

You can buy a dedicated battery/alternator tester which will verify that the problem is your alternator. Your local O'Reilly's or Advance Auto or what have you will probably do the test free. Sears will do it for $20. If that is your problem you can replace the alternator (two bolts and a nut plus moving the belt). For other ideas about diodes and such (which sounds like a great idea!) you may have to do some googling.

By the way, low voltage also can cause problems.
 

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I agree with the advice given so far.

Get the alternator tested. Usually free at the major auto parts stores.

If that's not it....I had the same problem with my 1999 GC about 5 years ago. I drew the line when the alarm would lock my ignition and wouldn't allow me to start the car.

I ended up getting a replacement BCM that did not have the alarm activated in it. Never had any more issues. I installed an aftermarket alarm with remote for security.

As these vehicles get older, the BCM's (which control the alarm and all the stuff you mentioned) slowly go bad....mainly the capacitors.

If you've ever had a leak below the driver side dash, water could get into the BCM and cause some issues.

One last demon I've found that can cause ongoing fuel pump/gauge problems as well as a few other annoying electrical problems was the grounding of the PCM where all the relays are.

If you don't get VERY good grounding you can have all sorts of troubles. I burned up the original and then a brand new fuel pump due to a bad ground and high resistance at the fuel pump relay. Learn about Noalox, dielectric grease and other compounds to start protecting those connections.

Good luck.
 

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Discussion Starter #6
Ok, all this sounds do-able. I'll get the alternator checked.

I'm pretty handy with a soldering iron; have never taken the BCM off but maybe the capacitors can be replaced and dry solder joints re-done, if the BCM can be taken apart?

Will look into dielectric grease and the grounding.

I've had electrical gremlins for years, will be great to get to the bottom of it!

Finally, I've asked this in a separate post but got no replies: the BCM reports an error code of "lift door zone switch defective". Anyone know where the "lift door zone switch" is? Haven't found anything by Googling.
 

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Ok, all this sounds do-able. I'll get the alternator checked.

I'm pretty handy with a soldering iron; have never taken the BCM off but maybe the capacitors can be replaced and dry solder joints re-done, if the BCM can be taken apart?

Will look into dielectric grease and the grounding.

I've had electrical gremlins for years, will be great to get to the bottom of it!

Finally, I've asked this in a separate post but got no replies: the BCM reports an error code of "lift door zone switch defective". Anyone know where the "lift door zone switch" is? Haven't found anything by Googling.
According to my mechanic BCMs never fail; it is always something else.

Now, do you know that the security system is not controlled by your key, only by your fob? In other words, if you use your fob to set the alarm and then unlock the door with the key, it will trip the alarm. The key does not enable or disable the security system. What does disable it is either unlocking it with the fob or turning the ignition on with the key.
 

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Discussion Starter #8
I don't see how the security system could be controlled only by my fob, since my fob hasn't worked for years. I never touch its buttons. And the dash display clearly says "security on" in the yellow lights. And turning the ignition on with the key is what trips the alarm to start sounding, until I get out and unlock - again - the already unlocked door, with the key.
 

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Discussion Starter #10
To rule out AC ripple from the alternator before replacing the BCM and checking grounds, this afternoon I put a multimeter across the batter. 14v DC, about right. But on the lowest AC setting (200V), it reads 30.6. How is that possible? It should be about 0.3v.

I saw a video on youtube showing this procedure where he also gets 30 volts AC, but with no explanation at all. Another, much better video shows a reading of 0.3 or so.

Could be a divide-by-100 error when reading the multimeter, but the instructions to the meter say nothing about reading it a different way for low voltages.

Huh???
 

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Discussion Starter #12
Ok, I think it's time to replace the BCM (I'll first remove it and see if I can get inside and possibly replace the capacitors, but assuming that doesn't work),

is there a way to avoid all the headaches I've read about online re: programming the BCM, the PCM not recognizing the BCM, etc.?

I understand that the model number on the BCM has to be exact. I've heard of places that sell refurbished BCMs pre-programmed according to your VIN number. Can someone recommend one of these places?

Thanks,
 

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Discussion Starter #13
mistypotato,
Two questions:
1) I looked around the PCM and the relay box and don't see an obvious grounding point. Do I need to take the PCM out? Any pictures online of what you're talking about?

2) Before I take it off (or buy a used one), can the BCM be easily gotten into and solder joints redone? Easy to replace capacitors (they're not surface mounted on the circuit board or something)?

Thanks,
 

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With electrical weirdness always check:

* battery
* alternator
* ground

And it doesn't hurt to have it tested at more than one place. I recently took a car to O'Reilly's and they said the alternator was bad. Took it to Advance Auto and they said it was the battery only. Changed the battery and no more issues.
 
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