07 Chevy trail-blazer charge light

[nick c]

I've spent the last few weeks reading threads on various forums and either my search skills suck or my problem seems to be just a little different then what I keep reading about.

The wife has a 2007 Trailblazer with the 4.2, 120k and motor/accessories are all stock as far as I know.

When the motor is running, the battery light is on. Not just the dim glow that seems to be associated with a faulty ignition switch but fully illuminated.

The gauge is reading right at 14 volts. When I check voltage at the battery when the motor is running I get 14.2ish with multiple meters (2 flukes, and 1 cheap-o meter I keep in my 4wheeling vehichle).

I took the rig down to my local parts store, and they load tested the battery, and said it checks out as good. They also did the start and charging system test with their machine. And all was good on their end. (I asked if I could do it so I could see the numbers myself but the gal said they aren't allowed to give up possesion of it).

This has been going on for probably over a year, and easily 10K miles. So I am confident the charging system and battery are working because i've never had it not start or act like it's a week battery. Recently my wife has started driving our suburban more, and the Trailblazer sits for 2 weeks or more at a time, and it still starts right up with out any issue.

I never worried about it since it didn't cause any trouble other then the idiot light but we've got it listed so I'd like to get it taken care of. If its not something I figure out here shortly I'll drop it at the shop when I get back from Sonoma.

Any thoughts, pointers or suggestions?

Thanks

 

[crash2]

This system is a complex system compared to what most are used to so the typical diagnostics don't apply.

There is no regulator in the alt, its controlled by a GBCM (that the little unit on the battery cable near the battery). It pulse width modulates the alternator to control charging.

Now here is the kicker and why as techs this **** isn't simple black and white. The GBCM controls the alt but the command to turn the lamp on is sent via the class 2 data line to the IPC. Now there is "NO" way for the normal guy to tell if the GBCM is faulty and sending the wrong command to the IPC, or the IPC is wrong in turning the lamp on.

From a techs prospective I cannot remember if in the data there is the info telling weather the lamp is being commanded by the GBCM or the IPC as its been some time since I have had to deal with that system (pretty robust).

More than likely its a false command Nick since the system is obviously charging--just hard to tell what module is telling it and why at times even the best of us have to take a logical stab at these things.

 

[skinny_pedal]

Pull bulb. Keep on keepin on:redneck:

 

[zukkev]

I'd pull the cluster and check the board connections, as the chev's of this era weren't exactly free from their cluster connection issues :redneck:...It's possible that it simply isn't receiving the signal from the GBCM to indicate it's charging. I believe my Solus Ultra does have a PID for Lamp illum.

 

[nick c]

Thanks guys, good info. That makes a lot of sense as to why I read so much BS on other boards with weekend wrenchers who keep saying to replace every thing under the sun. I hate that type of work.