Hi, First Post so bear with me Please.

I have a 2000 Pontiac Montana. 146k, 3.4 V6, with its few problems here and there, but rather trustworthy. However. 5 Days ago, While driving, everything jumped, (rpms noticeably, gauges, and overhead display ect.) and the 'SECURITY' light came on in the message center. From that point on, the engine would not maintain rpm, (would sway 1-200), the transmission would shift rougher, and the speakers would emit a clicking-static noise. Now, I am an Aircraft Mechanic, So I was able to troubleshoot it down to this.
-Idle rough, not maintaining rpm, trouble shifting
-Speakers emit clicking, regardless if radio is on/off Volume level
-only in drive
-Speaker noise worse when rpm'* are raised.
-Security light went out after restart, and stayed off
-No Codes or Engine lights
-Pulling Bat Cable to reset did nothing

This was the same day everything jumped. However again, it drove completely fine the next day, but has since started again, and has been getting worse.

Today, it is to the point where the speaker noise is much more prominent, in all gears. Rpm'* and Transmission still vary, almost like its trying to decide if it wants to shift or not. Overhead display is constantly resetting. Rough Starting, (if at all) and idle. and 4 times today everything resets, gauges flat line, all lights come on, everything resets, almost like you pulled the bat-cable. The security light also came back on temporarily in the mist of all this, only to go back out once restarted.

I have checked all fluids, the battery cable, battery, Alternator seems ok, and a few other things. This is obviously a serious electrical problem. A few shops I stopped at today suggested a bad ground somewhere, however I have little automotive electrical exp and I'm kinda scratching my head.

So, Any ideas on what may be causing this? BCU or ECU Maybe? The Owners Manual says when the security light comes on, it means the PASS KEY III module is malfunctioning, however I am unsure where that is to check it.

It seems to continue to start, (I have to give it some gas to go) and stay'* running for the moment, however as stated, it seems to be getting worse. (if I can just get to work the next 2 days then I'll have some time to work on it, no other car)
I can chase wires if I need to, but I have no clue where to start. I hoping I can get a few other suggestions here before it costs me 1-3oo$ at a shop just to tell me what it is....
I"ll be checking fuses now as well....



My Forward Thanks to any replies and or suggestions!

Check the alternator and battery to make sure the car is running, and charging, at 13 to 14 volts. Other than that it does sound like a bad ground, although the sudden onset is puzzling. The Bonnevilles have ground busses near the driver'* seat, but I don't know where it is located for the Montana. You also need to check all gounds throughout the vehicle. Perhaps someone with a Montana can provide that information. Danthurs has one and I am sure there are others.

SOLVED!


The lead from the battery cable to the fuse box on the passenger side of the engine bay had been chafing on the accessory belt pulley. There was two places it was chaffed. One spot was about half way through, but was corded, leading me to believe this had happened prior. Two, about 2" down on the wire, was another spot, about 1/4 the way through, and was fresh.
Weather this cable had been placed there by me when I changed 3 of the plugs/wires, or by the mechanic when I took it in to have the other three done, is beyond me. However, after setting it back in place, it seems to just be in that tricky spot there, telling me this could happen to anyone if not checked after some work has been done.

I've done a quick fix to the wire, and taped it up, and it now runs and drives fine. A quick trip to the store for some wire and such, and I'll be good as new.


Thank You!