1998 Plymouth Voyager BCM - Power Loss at Idle

1998 PLYMOUTH VOYAGER
101,000 MILES • 6 CYL • FWD • AUTOMATIC
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WILMINGTECH
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I have a 1998 Plymouth Voyager. It initially had a BCM problem (lights would randomly turn on/off while ignition was off). We took it to the dealer and they had to replace the BCM 5 times. Each time we would get the car back it would have something else quirky with it. (lights would not turn off with iginition off, wipers would not turn off, gauges would not work) We have finally got a BCM that seems to work. There is one minor quirk though and I want to make sure it is the BCM this time. The car seems to run fine while driving but when Idle it seems that it is losing electrical power. The digital readout for the mileage and gear indicator (P-D-N-R) start to dim and the fans for the ac noticbly drop to a lower RPM, the radio will lose power and then come back on. Once the car accellerates and goes back to cruising speed all the problems go away. We have replaced the battery and the Alternator and the dealer is telling us that the BCM is not at fault and there is an electrical problem with the van. Before paying 90/hr for someone to troubleshoot I figured I would ask for some expert advice here at 2carpros. Thanks for any information you can provide.

-Sean
Aug 12, 2010 at 11:09 AM
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MERLIN2021
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Unfortunately, this will be hard to prove, but the BCM problem may now be a PCM(main computer) problem, this controls the charge rate of the alternator. That, or the wiring in the charging system is in need of repair, Could be battery cables need replacing, or at least a clean and tighten of both ends of both cables. Bad battery negative terminal(ground) connection may be the problem. Try this and post any codes that cone up.
Turn the key from off to on three times, on the fourth one leave it in the on position, count the flasshes...22 would flash as 2 blinks, then a short puase, then 2 more blinks...if several codes are stored, the pause is longer between codes, code 55 will be the last code...do this and post all codes found...

Some Chrysler work like this:
You can try a self-diagnostic test. To activate self diagnostic program:

With the ignition switch in the OFF position, depress the TRIP and RESET buttons.
While holding the TRIP and RESET button turn the ignition switch to the ON position.
Continue to hold the TRIP and RESET buttons until the word CODE appears in the odometer windows (about five seconds ) then release the buttons. If a problem exists, the system will display Diagnostic Trouble Codes (DTC's). If no problem exists, the code 999 (End Test) will momentarily appear.
Aug 12, 2010 at 4:15 PM
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WILMINGTECH
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Merlin,

Thanks for your help with this. Greatly appreciated. I was unable to get any flashes with the key off/on. I was able to use the self diagnostic test holding the TRIP and RESET buttons down. The code 999 appeared and then it went through self check 0, self check 1, etc. The battery cables have been replaced, I have a hard time believing that the cabling is bad. On visual inspection it looks in good condition. Would I be able to check the wiring condition by testing the voltage across the Negative on the battery and the ground on the Alternator or the positive on the battery and the positive contact on the alternator?
Another thing I wanted to ask - Could it be possible that the Serpentine belt is loose enough where when the car idles it is losing power from the alternator? Is there any way to check this without having to bring it to the shop?
It seems pretty tight to me but I am not a mechanic.

Again - thanks for any help or insight you can provide.

-Sean
Aug 13, 2010 at 10:48 AM
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MERLIN2021
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Ok this self diagnostic covers only P codes, so it's still possible the B and U codes are stored, and we need a scan tool with that capability, Yes you can voltage drop test the cables by measuring battery voltage, then do the drop tests you described. If the pcm were no good we should have got a P0600 series cod. so it is in either loose connections or grounds... Scan then search!
Aug 14, 2010 at 7:27 AM
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WILMINGTECH
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This is a few months since I last posted and the problem has since been fixed. The issue was that there was an aluminum wire block that was connected to the battery terminal on the positive side (seems it was there since we bought the car). There are two cables connected to the positive terminal. One was connected through the aluminum wire block. Once I removed the wire block and connected the wire directly to the terminal the problem went away. This van has been running great since.

Thanks Merlin for all your help.
Nov 11, 2010 at 12:10 PM
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