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Discussion Starter · #1 ·
Has anyone added a voltmeter to their Terrain or Nox? I added one to mine and it shows 14.5 to 15 volts right after start up, then drops to about 12.8 after driving a while. Is that normal? I would have thought it would stay around the 14 volt area. If any one of you techs has any insight, please let me know.
 

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rickbb63 said:
Has anyone added a voltmeter to their Terrain or Nox? I added one to mine and it shows 14.5 to 15 volts right after start up, then drops to about 12.8 after driving a while. Is that normal? I would have thought it would stay around the 14 volt area. If any one of you techs has any insight, please let me know.
Most car's alternators run the electrical system at about 14 volts, and then when the car is shut off, the fully charged battery should read about 12.8 volts. Unless your alternator is not working, it should not be running a 12.8 while the car is running, unless you have a big electrical load i.e. heated seats, rear defogger, heated mirrors. However, I doubt if your alternator is not working, because you would probably have a dead battery by now.
 

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Discussion Starter · #3 ·
There was no load on the system at the time. My guess is that the alternator reduces the output when it senses the battery is at full charge. If I shut off the car and re-start it, the voltmeter shows 14.5 again.
 

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rickbb63 said:
There was no load on the system at the time. My guess is that the alternator reduces the output when it senses the battery is at full charge. If I shut off the car and re-start it, the voltmeter shows 14.5 again.
That makes sense - it would be a smarter way to run the system. I think they stopped putting voltmeters and ampmeters in cars becuase they were getting too many people complaining about "problems" that weren't really a problem. Also why they have the temp guage with such a dead-band at its normal operation level.
 

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I added a voltmeter to the factory DIC. I see over 15 volts regularly although i don't recall seeing below 13 although if you were at idle in ECO mode I guess I could see it.
 

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This wouldn't happen to be a voltmeter that plugs into the cigarette lighter, would it?
 

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Discussion Starter · #7 ·
This one is wired into the fuse panel. I installed it near the front accessory plug. It seems to "jump" from 15 volts to 12.5. Looks like the alternator switches to a lower output. If I shut it off and restart it, it goes right back to 15.
 

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rickbb63 said:
This one is wired into the fuse panel. I installed it near the front accessory plug. It seems to "jump" from 15 volts to 12.5. Looks like the alternator switches to a lower output. If I shut it off and restart it, it goes right back to 15.
I would throw a multimeter on the battery and check the voltage there. It is possible an accessory is drawing current and causing the circuit you have the voltmeter wired to drop.
 

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Discussion Starter · #9 ·
Thank you, that covers it. I'll keep an eye on all those circumstances. Makes sense though, trying to save fuel.
 

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I have recently been watching the voltage reading on my 07 Torrent and see the same thing. The problem is I sometimes get a no start!! The voltage reads 12.2 - 12.5 when I key on. If it starts, the voltage jumps to 13.9 - 14.3 volts. Sounds good except sometimes it starts dropping soon after that back down to about 12.8 volts or less in the next 3 minutes. Often it will stay there until I stop and (hopefully) restart. Then it cycles all over again. Sometimes it will ramp back up to 13.8 volts and then back down, sometimes it stays at 13.8 V throughout the cycle. I have had the battery replaced and battery connections re-tightened by my dealer as "fixes". I still get no starts occasionally and I find that the battery needs recharging when I hook it up to my charger. I had the alternator and battery checked at Advance Auto and they said they are good except for low state of charge on the battery. I would certainly like to understand if there is some other circuit controlling the alternator output that could be the problem. Can any GM engineers explain how the charging circuit works and is controlled??
 

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I was going to quote the service manual, but turns out - the description of the operation of the charging system runs 5 pages. So I'll summarize instead. The computer controls the voltage to regulate the charge of the battery based on a pile of parameters with the objective being (among other things) long battery life. There are 6 modes of operation for the charging system. Mode is set by the BCM which tells the generator what voltage it wants via the ECM. "Charge mode" is entered if any of the following are true: Wipers on; HVAC/defog on; battery temp 0 C (32 F) or lower; battery state of charge less than 80%; speed greater than 145km/h; Sensor fault; or system voltage is less than 12.56 V. Generator output will be between 13.9-15.5 V depending on state and temp. In Fuel Economy mode, output will be between 12.5 - 13.1 V. Start Up Mode the BCM asks for 14.5 V for 30 seconds before selecting other mode. Voltage Reduction Mode is set when the temp is 0 C (32 F) or higher; battery current between +1 and -7A and generator duty cycle less than 99%; in this mode voltage is 12.9 V.

I'd offer to scan the pages but my scanner recently died.
 

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CuHead said:
I was going to quote the service manual, but turns out - the description of the operation of the charging system runs 5 pages. So I'll summarize instead. The computer controls the voltage to regulate the charge of the battery based on a pile of parameters with the objective being (among other things) long battery life. There are 6 modes of operation for the charging system. Mode is set by the BCM which tells the generator what voltage it wants via the ECM. "Charge mode" is entered if any of the following are true: Wipers on; HVAC/defog on; battery temp 0 C (32 F) or lower; battery state of charge less than 80%; speed greater than 145km/h; Sensor fault; or system voltage is less than 12.56 V. Generator output will be between 13.9-15.5 V depending on state and temp. In Fuel Economy mode, output will be between 12.5 - 13.1 V. Start Up Mode the BCM asks for 14.5 V for 30 seconds before selecting other mode. Voltage Reduction Mode is set when the temp is 0 C (32 F) or higher; battery current between +1 and -7A and generator duty cycle less than 99%; in this mode voltage is 12.9 V.

I'd offer to scan the pages but my scanner recently died.
Wow - not like the "good-old" days when everything was simple ! Sounds like they optimized the aternator to extend battery life.
 

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Wow again. Great information!! So it seems that the voltage readings I am getting may be "normal". But if my battery is not reading as charged by the guys at Advance Auto, what could be the issue?? How does the BCM sense the state of charge?? Does the ECM also make decisions or just pass the signal through? Where is the best place to get a service manual??
 

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Try Helms.com
 

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Try helminc.com. The price $200 for the 3 volume set. I gets you
8 to 9 inches of manuals with a LOT of good stuff. It will keep you
occupied for quite a while.

I am ordering the Terrain set in about 2 weeks
 

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Whoa. $200.00???? Anyplace to view the section I need?? I would just like to know how to check the various modes of alternator operation.
 

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The shop manual is expensive for 5 pages. However, it does make for good reading.
I have gotten one for each car that I have purchased. I just like to know how every
thing works and is tied together, this is especially true with today's computerized
cars.
 

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Iliketerrain said:
The shop manual is expensive for 5 pages. However, it does make for good reading.
I have gotten one for each car that I have purchased. I just like to know how every
thing works and is tied together, this is especially true with today's computerized
cars.
They've raised the price, I see... I paid $150 for the 4-volume set shortly after I bought the vehicle. I looked at it this way, $30G for the machine, $150 for the manual isn't much. It has indeed helped me develop a better understanding of how the machine works (vs. my old-school knowledge from my previous vehicles).

I must say however that it is bigger than the flight manual for a dc-9 :eek:

LOT, I'll see if I can take decent readable images with my camera phone, but FYI I'm talking the 2011 Terrain/Nox manual, so the 07 Torrent may be different.
 

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CuHead said:
I must say however that it is bigger than the flight manual for a dc-9 :eek:
I'm sure the service manual for the DC-9 wouldn't fit in the cargo area of the Terrain/Nox. :thumb:
 
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