2001 Silverado 1500: volt gage fluctuates

[RayInAlaska]

I will start with an apology in case I am not posting in the right forum.

My 2001 Silverado's volt gage fluctuates from 14 to 16 volts when the engine is idling or when I am driving the truck. I replaced the original alternator with a new one just because the old one had a lot of use on a truck that already had around 111,000 miles.

The new alternator worked wit a hitch for over two years until the volt gage pointer started moving or fluctuating as explained above. I assumed that either the voltage regulator (or the rectifier) was malfunctioning, so I replaced the alternator with a new one since it is under a lifetime warranty, but the problem continues, even with this last brand new alternator.

When I check the alternator's output to the battery with a Fluke multimeter, or with a digital battery/alternator tester I have, the alternator is working perfectly at 13.2 VDC base charging voltage, and a maximum of 14.5 (no fluctuations whatsoever on the meter and tester, just the volt gage in the dash).

I assume that the voltage regulator in inside the alternator, and that the two new alternators aren't causing the problem. Do you have any idea what could be causing the volt gage to fluctuate like that? The only plug on the alternator is located right on top, and has two wires that run toward the trucks cab. I imagine that these two wires lead to the volt gage. I have checked the plug contacts, and everything seems to be clean and solid, but I haven't been able to trace the wires all the way to the gage.

Thanks in advance!

[biketopia]

odd are it's the gauge (stepper) motor. They do fail and or get sporadic, usually it's the tach or speedo put all of them are known to have issues since it's the same motor. There's companies online that will refurb your dash or you can do it your self. There's lots of how-to info online and the motors are cheap enough on ebay or amazon. If you have a scan tool that can monitor some data like voltage that will tell you what the ECU and seeing and if it's staying steady and the gauge is moving around that's a pretty solid confirmation your gauge motor is on it's way out

[RayInAlaska]

Originally Posted by biketopia

odd are it's the gauge (stepper) motor. They do fail and or get sporadic, usually it's the tach or speedo put all of them are known to have issues since it's the same motor. There's companies online that will refurb your dash or you can do it your self. There's lots of how-to info online and the motors are cheap enough on ebay or amazon. If you have a scan tool that can monitor some data like voltage that will tell you what the ECU and seeing and if it's staying steady and the gauge is moving around that's a pretty solid confirmation your gauge motor is on it's way out

I appreciate your response. As I mentioned above, I used both a very accurate Fluke multimeter to check the alternators output, and also an alternator/battery tester, and the alternator output was correct and steady, while the gage fluctuated. The alternator is brand new, and it replaces another alternator that was under warranty because I thought its rectifier (or maybe the voltage regulator) was malfunctioning. Anyway, I will see if I can repair the gage; otherwise I will leave it alone until the next summer.

Thanks again!

[hatzie]

The instrument clusters have an onboard surface mount DC-DC converter circuit and a raft of surface mount pull up and pull down resistors. The solder joints tend to fracture from thermal cycling.

The stepper motor problems are in the 2003-2007 clusters and some of the 2007-2014 clusters as well.

The 1999-2001 clusters used board mounted air core meter movements like the T400 clusters. These are a bit more reliable than the 2003-07 stepper motor gauges.

I'd send the cluster out to be repaired. United Radio has a good reputation.