On my 2005 Yukon the alternator no longer drops off for that fuel saving mode.The amp gauge shows a constant charging of to the largest line between 14 and 19 sometimes going beyond that mark.Did not do this in the past,the amps always dropped back to 13 something.Any ideas. Has 115,000 on it.
Amp gauge
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You have an amp gauge in the cluster? It's probably a voltage gauge. 
Trey Hardy
8” fabtech icon coilovers uniballs 24x14on35/15.50
If you don’t trust the one on the dash you can get a volt meter that mounts in the dash or one of your charging ports to read the voltage.
I have a aftermarket amp in my Tahoe and on the bass knob there is a voltage meter that I watch but in your case the cig lighter one would be fine
nonickatall
Full Access Member
Its not an amp gauge its a volt gauge.
If you gauge shows more that 14-15V you have a defective gauge, what is not very likely, because a defectice gauge would rather show to less V than to much.
More likely is you alternator's charge controller is probably defective. This is usually integrated into the alternator and can be submerged individually.
But I've read somewhere in this forum that our cars have the charging control integrated into some control unit.
In any case, you have to fix this problem immediately, because if the voltage is too high, it can destroy other electrical systems, e.g. controler in your car.
If you wreck your ecm by that, its gona be a expensive repair...
If you gauge shows more that 14-15V you have a defective gauge, what is not very likely, because a defectice gauge would rather show to less V than to much.
More likely is you alternator's charge controller is probably defective. This is usually integrated into the alternator and can be submerged individually.
But I've read somewhere in this forum that our cars have the charging control integrated into some control unit.
In any case, you have to fix this problem immediately, because if the voltage is too high, it can destroy other electrical systems, e.g. controler in your car.
If you wreck your ecm by that, its gona be a expensive repair...
swathdiver
Full Access Member
This is usually a sign that your battery is failing to maintain a charge and the alternator and computer are doing everything they can to keep you from getting stranded.
How old is your battery? Has the truck been sitting and or making lots of short runs lately?
nonickatall
Full Access Member
Are you sure? Normalwise the charge controller delivers the voltage/ampere which is needed to charge, apprx. 14,8 Volt, but never more than 16V. The ampere goes up when the battery is low, but the Voltage remains stable, as far as there are enough revolutions for the generator.
I had this happen on my 14 Sierra. I noticed the gauge was reading 15-16 volts. Upon testing my alternator the gauge was right. We caught it before it killed my battery or anything else. Most parts stores test batteries and alternators for free.
