Newer trucks have a current sensing module on the negative battery cable or right at the battery post. It determines the current needed to charge the battery in conjunction with the BCM/PCM. They can go bad as they are a Hall effect device.

 

Is it a Big DIY Job to change the current sensing module on a 2002-2006 Chev Avalanche? (Any short cuts?)

 

Yes, after much poking around I determined that the sense wire S terminal connection (its a three wire plug) on the rear of my alternator was somehow experiencing a voltage drop and hence not getting an accurate reading. Sense wire thought battery was being charged at 14.5ish when in reality it was at least a full volt higher. I traced the voltage drop all the way back to the engine fuse box. Alternator is kicking out between 15.2 and 15.8 volts depending on rpm but the voltage reading along the sense wire is a full volt lower...14.2 - 14.5. Quick fix....I unplugged the fuse feeding voltage to sense wire...sense wire now receives zero volts. Alternator reacts by pushing out 14.4ish. I am assuming when no voltage reading is received, the alternator defaults to that number. Now, the next question is about how to go about fixing this....The wire resistance issue is somewhere between the fuse and the battery....in other words either buried in the harness or im not sure where else. I need to crawl under and check voltage at starter as I think wires junction from there to feed the fuse box. Either way, I guess im going to have to run a new wire. Any issue with running a fused wire directly to alternator sense input?...Id just remove current wire from fuse box and run another wire altogether....or just leave fuse unplugged. No harm in that right?

 

I'm wondering if you have a faulty ground somewhere since the BCM cotrols the charge rate from the neg cable current sense wire device. It tells the alt what charge rate. All of this is referenced to ground.

 

hmmm...I will check voltage drops this afternoon. If the alternator case to battery negative post and alternator b post to battery positive post all come back less than .2 volts though that would eliminate that possibility, right? I attached wiring diagram Im working with. Ive traced back to fuse 48 on alt2 image. That fuse has a voltage drop over 1 volt relative to battery post voltage. I should also mention that the 2006 silverado I acquired was only its guts. It was hacked into a van project I am working on but everything is stock GM parts and wiring far as I can tell....

 

So, I did some more voltage drop tests....I have a voltage drop of 1.1 volt when the engine is running on these fuses...the pink wire feeding them also has a 1.1 volt drop. I'm trying to chase this down to the wire giving me issues....not too skilled at reading these diagrams...looks like a bunch of wires feed into the pink wire feeding these two banks of fuses. Where do I need to dig next? I'm not sure how power is flowing here or where to chase this voltage drop from this point...

 

Ok looking at your diagram (hope its the correct one for your truck) then if you measure from the battery ground post to these fuses and you have a drop of 1+ volt then the problem points toward the battery cables and fuse box. All power for these fuses comes thru that fuse box on a stud connection from the battery.
Looking at Alt1 pic I see there is a fusible link from the battery + to the fuse box stud. That pic shows 3 wires connected together at the starter motor stud thru that fusible link to a splice that goes to the Alt stud and that splice point continues on to the fuse box stud to supply the main power to the fuse box. I would open that fuse box to see why the voltage drop. Check all these points for tightness and good crimps. GM had defective cable crimps at times on these trucks.

 

They also had fuse panels that corroded, you may have corrosion under the panel.

 

Well, I figured it out...it's 70 percent crappy design and 30 percent corrosion. Why would engineers connect the sense wire which gives alternator info needed for output so far from battery. It's literally downstream from battery of about 15 feet of cable and routed through ignition switch. No wonder the sense wire is getting a huge voltage drop and overcharging to compensate. So now the question is how to fix it....should I just connect sense wire with its own wire to battery with inline fuse?

 

Where is the corrosion? Since it runs thru the ignition switch then perhaps that is where your voltage drop is. Any new wiring needs to follow the same path. That means thru the ign switch so that sense voltage it is off when the ign is off. I would fix the problem where it is.

 

About half of the voltage drop (.4 volts) is across the switch...easy enough to replace. The other is down the wire that runs from the switch through the firewall to the fuse which then feeds the sense wire. Not quite sure how to dig into this harness...do both ends just disconnect at firewall? Seems like no fun and a lot of trouble. I should also say that two other circuits off this fuse are not important to me...namely AC...which I deleted...and ABS which I'd like to delete. (I'm an automotive minimalist...can't stand extra **** that costs money and breaks.) I guess I could always use a relay to turn off voltage to alternator if I ran wire directly to sense terminal on alternator...or purchase new ignition switch and instead of running wire to engine fuse box...just put inline fuse to sense wire.

 

Not a big project. If I recall correctly, you have to disconnect the cable at the body connection because it can’t slip over the battery end.

 

I'm hoping it doesn't come to that, but I sure appreciate your input if I have to. I just replaced the third "used" alternator from PicknPull and it seems to be holding steady at about 14v for the last couple of days. 3 different alternators; no wonder I can't win a lottery. Thanks Cowboytrukr.

 

Guess what! My Avalanche overcharging problem came back AGAIN. Well...I read up on the GM automatic voltage module in greater detail and I suspected even more that "I" was the real cause of the problem. Last winter, because I wasn't going to use the truck much, I installed a screw on/off disconnect device on the negative battery cable. So, today, I removed that device, restored the original connection, and the truck is charging right on the MONEY. I suspect that I, by installing this disconnect device on the negative side, that I unknowingly, added some resistance to the battery circuit which lowered the voltage enough to fool the "sarvc module", and to cause the PCM to increase the alternator voltage unnecessarily. Geez.. do I ever feel sheepish about this! Thanks for your attention Cowboytrukr.

 

Listen, Brutha. We’ve all been the brunt of our own mistakes and object lessons. Glad you figured it out.