2007 Montana SV 6

[sonyblue]

Hello to all!
I have an 2007 Pontiac Montana SV6 that wont start in the cold days. Here in Calgary we have a very cold weather this year with temperature going easily under -25 C. My car even plugged all night won't start at all in the morning.
This is the second battery on the vehicle, an aftermarket Motomaster way more powerful than the factory one.
If I connect the battery charger it will take no longer than 10 min to be able to start the vehicle.
Last spring the car was in a GM dealership for the same problem and they could not find anything wrong with the charging system and they sent me a letter stating that my alternator is "intelligent" and will adjust the charge accordingly with the load.
During summer at the return from my 1 week vacation I had the surprise to see my car was completely dead so I decide to change the battery... Now when the cold weather started the same thing is happening. All dash board instruments are going crazy, when you turn the key to start the engine, the horn is starting and all the gauges and dashboard lights are going nuts. You can hear relays and parasitic noise from the radio and the car won't start.
As I said 10-15 min on the charger and after on "boost assist" are enough to start the beast. I did all the parasitic tests with my multimeter and couldn't find anything.
I really need some advice before I will send the car back to dealership to find out how "intelligent" is my alternator and how shitty is my ECM.
Can somebody tell me if this is a generic problem with Pontiac Vans made after 2005, cause before I had a 2001 Montana that never did this.
Thanks

 

[Steelcity]

What is your charging voltage at the terminals when the van is running ? Also when the van is off ?

 

[sonyblue]

I went with the car today at a Certigard location and they did complete drain, charge and parasitic drain tests. They couldn't find anything unusual just couple of codes but they told me were not regarding charge or start up.
I told them again the story about the gauges and the fact that when is cold and I'm turning the key, instead of turning on the engine my horn start...and they told me that ....they/I found the problem....the second car's computer is the problem...or Body Control Module (BDM). They sent me to a GM dealer, because they can not rewrite the computer.
At the dealer they didn't want to hear about my story...but when I showed them the paper from Certigard situation changed and now I have an appointment for next week to check/replace my Body Control Module

 

[ianmcdca]

You absolutely sure this wouldn`t be covered by a warranty if you pressed a little harder???

It could be a BCM thing. the 'Body Control Module' controls things like locks, power windows, alarm, anti theft stuff. I`ve also had an ignition switch go bad where wierd lights and things were happening. This wasn`t a 'Passlock' issue either. BUT FIRST:

Don`t assume because it`s a newer vehicle that rust or corrosion can`t affect things.

Is it holding a charge just not wanting to turn over? Or draining power?

The only other thing I can think of is either a poor ground or poor connection from the Auxiliary battery post (Red post) to the starter. Even a newer vehicle can have a poor ground or power connection. On one of my Chevs, I had to run a separate wire from the Aux. post to the starter. The alternator feeds the battery through the starter on some models. Also, sometimes the bolt on that aux. post gets corroded or becomes loose. I cant explain how, but on another of my vehicles it used to come loose and I had to tighten it weekly. Tried a lock washer and a double nut! Still came loose. Also, tighten the bolt on the starter as well as the smaller wire from the starter solenoid. Unfortunately few repair shops can reprogram a GM BCM. But, I`d make some more calls first to other repair shops and ask them if they can 'program a new BCM' on your van.

I`ve had 3 vehicles all chevs not start in the same way you`re describing until I put cables on and gave them a boost. Battery tested good in each case. That`s when I tightened the bolts. They are all fine now. Just didn`t have the dash light up

Either way, see if you can get an aftermarket BCM. They do sell them. Just not sure if they do for your year. Then, take that new BCM to the dealer and have them install and reprogram it. You might save a few dollars.

By the way...alternators have been 'Intelligent' for years now....mechanics, not so much.
Let me know.

Ian

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[peices0res]

How much did you end up paying at the dealership? The security light is on on my wife's 03 Montana and now the starter and injectors have been shut off. It did this last week, but I was able to leave the key in the on position for a while and got it to start. The ONLY electrical that still worked was the headlights and wipers. None of the guages would work, the ABS was saying it was off, the radio would not work, the electrical doors were not working, basically nothing was working. I took it a couple of places and none of the diagnostic hookups would even read the PCM. Not even while it was runing. I'm going to tow it in to the dealership tomorrow and am just curious how much I'm going to be looking at.