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Chevrolet Tahoe: My chevy Tahoe 2012 5.3L spikes up to 15.8

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My chevy Tahoe 2012 5.3L...
My chevy Tahoe 2012 5.3L spikes up to 15.8 volts. Its runs about 14.9V at the cigarette lighter on the dash (Flute VOM meter). Dealer replaced the Alternator, but no change. Is the voltage regulator in the Alternator or the Body Control Module?
Submitted: 2 years ago.Category: Chevy
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Customer reply replied 2 years ago
Driven a bit longer after the alternator was replaced and the voltage is even higher - showing 14.9 to 15.5v on the ODB II connector and 14.7 to 15.3 on my flute VOM meter in the cigarette lighter. Note: The highest voltage doesn't last long - typically only shows for 2 to 4 seconds before returning to 14.7volts (flute VOM meter).
Also - I have replaced 3 headlights bulbs, and two brake lights over the past 6 weeks..
Any advice is welcome...
Customer reply replied 2 years ago
Note: When the voltage goes high at night - the headlights get noticeably brighter for a few seconds.
Answered in 20 hours by:
7/26/2015
Chevy Mechanic: ASEMaster35yrs, Chevy Technician replied 2 years ago
ASEMaster35yrs
ASEMaster35yrs, Chevy Technician
Category: Chevy
Satisfied Customers: 2,095
Experience: ASE Certified since 1972,Master Auto tech,Heavy Truck Tech ,chev dealer tech
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This problem can be caused by a sulfated battery or a poor connection. First have your battery load tested and checked out. Next check ground connections. There was a TSB out on ground wire connections.
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Chevy Mechanic: ASEMaster35yrs, Chevy Technician replied 2 years ago
If battery tests out good, Check all battery connections and grounds.2012 Chevrolet Tahoe Electrical System Service Bulletin 376527Action Number: 10056237Service Bulletin Number: 376527Report Date: May 01, 2014Component: Electrical SystemSummary: General motors: due to loose ground terminal connections, in some vehicles and trucks experience, accessories malfunctions, dic messages, ipc warning indicators, ses light on.
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Chevy Mechanic: ASEMaster35yrs, Chevy Technician replied 2 years ago
See all recalls & TSB's t https://www.automd.com/tsb/chevrolet_m/tahoe_mm/2012_y/
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Customer reply replied 2 years ago
Battery was replaced about 4 months ago (thinking about this it was about time I started to have the headlights/brake lights burn out...)
Although I've replaced more headlights in the past 6 to 8 weeks...So far, after the alternator was replaced. I have cleaned both battery terminals, removed and cleaned the 175amp fuseable link at + battery terminal , removed and cleaned cleaned ground to engine (front passenger side of engine), removed the fuse assembly (fuse box under hood) and cleaned all contacts (used a pencil eraser to clean), removed each fuse and cleaned all fuse contact (again pencil eraser), removed and cleaned contacts to each of the relays (again a pencil eraser)....Know of any other grounds I should be checking? TSB 376527 isn't very specific as I suspect there might be more than 1 ground wire... (already removed and cleaned the ground to the front passenger side of engine block).Do you know were the voltage regulator is? Is it in the alternator or the body control module?
Chevy Mechanic: ASEMaster35yrs, Chevy Technician replied 2 years ago
The regulator is internal in the alternator.
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Chevy Mechanic: ASEMaster35yrs, Chevy Technician replied 2 years ago
The TSB involves replacing the battery cables. Make sure there is good clean connections on both sides of the bolts the screw into the battery and there is no paint or corrosion where the other ground connections meets the firewall block and/or frame.
It is normal for it to charge between 12.5 to 15.5 volts.
The alternator is controlled by the computers for fuel efficiency and to keep battery maintenance minimal.
This is straight from the description and operation
The BCM will enter Charge Mode whenever one of the following conditions are met.
•The wipers are ON for more than 3 seconds.
•GMLAN (Climate Control Voltage Boost Mode Request) is true, as sensed by the HVAC control head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.
•The estimated battery temperature is less than 0°C (32°F).
•Battery State of Charge is less than 80 percent.
•Vehicle Speed is greater than 145 kph (90 mph)
•Current Sensor Fault Exists
•System Voltage was determined to be below 12.56 volts
•Tow/Haul Mode is enabled
When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9–15.5 volts, depending on the battery state of charge and estimated battery temperature.
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Customer reply replied 2 years ago
Thanks for the information. I'll go back over the grounds again and check the quality of the cables. There was a small amount of corrosion on the engine ground block (front passenger side of engine), but is cleaned right off with a small wire brush, didn't look like any cable corroded away.
Also sounds like 15.5v isn't unusual for this car.
Thanks for the advice,
Chevy Mechanic: ASEMaster35yrs, Chevy Technician replied 2 years ago
The main problem found with the battery cables were at the crimp where the cable end was not making good contact so mostly the negative cable should be replaced. The contacts at where the cables meet the metal should be cleaned and free of paint or corrosion. Having a good connection is very important because the alternator will produce enough voltage to overcome the resistance in the circuit. 15.5 is too high and means there is too much resistance in the circuit. 15 volts is acceptable. Corrosion can occur inside the cable itself and you would have to cut out the insulation to see it so it would be easier to just replace the cable. Spaying a little WD-40 at the ends will reduce the possibility for corrosion.
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