2001 Sierra Amp Problem

kc24clark · March 2, 2009

On my 2001 Sierra, when I really rev the engine like passing a car, my amp gauge drops down to around 7 amps and if at night, the lights go dim until I back off back to normal acceleration. I had the alternator checked, it is putting out plenty of amps, I replaced the belt tensioner assembly and the belt appears in good shape. At first I thought it was a short of some sort, but just not sure now. Anyone else had this problem????

bill190 · March 2, 2009

When testing the alternator, did they rev it up to the same speed as it is going when you are reving your engine?

VR021302 · March 2, 2009

Sounds like the regulator is bad, but the bench test is not always a guarantee either.

kc24clark · March 3, 2009

Sounds like the regulator is bad, but the bench test is not always a guarantee either.

No they just did a bench test at the local auto parts store, they didn't rev it up any. If the regulator is going bad, where is it located on the vehicle and is this easily replaceable by me?? What would be your next step?? Thanks!!

bill190 · March 4, 2009

Going by the amperage gauge, which should show the amperage coming from the alternator, if I am correct, it is showing less amperage at higher engine RPM's. So I would first think the alternator. Perhaps at higher speeds, the centrifical force causes something to have a poor connection?

Sort of like a water well pump. Pump slow and it pumps water. Pump fast and it pumps less water = problem with pump.

Also in my experience, mechanical things wear out and break first. Electronic things tend to last a long time. So another reason to first suspect the alternator.

Then how old is the alternator? If old and it will need replacing anyway, then I would replace it just for preventative maintenance reasons.

If that does not work, then I would replace the voltage regulator. The location for this would for sure be shown in a factory maintenance manual and probably in a 3rd party maintenance manual, but might not show your exact vehicle (which can make things confusing!).

If neither of the those work, then I would take it to the dealer as the problem would be complex to troubleshoot.

kc24clark · March 5, 2009

Going by the amperage gauge, which should show the amperage coming from the alternator, if I am correct, it is showing less amperage at higher engine RPM's. So I would first think the alternator. Perhaps at higher speeds, the centrifical force causes something to have a poor connection?

Sort of like a water well pump. Pump slow and it pumps water. Pump fast and it pumps less water = problem with pump.

Also in my experience, mechanical things wear out and break first. Electronic things tend to last a long time. So another reason to first suspect the alternator.

Then how old is the alternator? If old and it will need replacing anyway, then I would replace it just for preventative maintenance reasons.

If that does not work, then I would replace the voltage regulator. The location for this would for sure be shown in a factory maintenance manual and probably in a 3rd party maintenance manual, but might not show your exact vehicle (which can make things confusing!).

If neither of the those work, then I would take it to the dealer as the problem would be complex to troubleshoot.

That is correct, when the motor is at a higher RPM, it seems that is when the problem occurs. The alternator is about 1-1/2 yrs old, the pulley spins freely when the belt is off it, but like in the earlier post, when I took it off and had it checked, they just did a normal bench test. I think I will go ahead and try replacing it and hope that fixes the problem. Thanks for the advice.