I have a 2002 4.2L Trailblazer LS that has started to experience slight flickering headlights, dashboard lights, and dome lights when the engine is running. The flickering is very fast, where the lights flicker probably 5 to 10 times per second. It appears to get worse when you increase the RPM. The voltage fluctuation varies quickly from about 14.2 to 14.5 volts. If you are coasting and the idle is around 1000 RPM the flickering goes away and the voltage stabilizes. (I have a radar detector that has a volt meter readout.)
Another related symptom is sometimes when letting off the gas to decelerate (before braking) the voltage will drop from 14.x to 12.8 for about a second and then return. The lights will dim momentarily.
Sometimes the voltage fluctuation is 0.1 to 0.2 volts and the flickering is not noticeable.
I checked my battery terminal connections. I also checked several ground points. The resistance from the negative battery terminal to the engine chassis and to the frame of the car is approx. 0.1 ohms or less. The alternator puts out about 14.2-14.5 volts. The battery puts out about 12.5 volts (open circuit). Both the alternator and the battery passed with handheld testers at Autozone and Oreilly. The battery is 1 year old.
My alternator is original from the factory. I noticed there is a connector from the alternator that has 2 thin wires going into a wire wrap. I assume one is the turn on signal and the other for the PCM to regulate the alternator voltage?
Could I have a bad voltage regulator, which I think is part of the alternator assembly? Or could my serpentine belt be slipping and wearing out? I don't notice any obvious squealing sounds under the hood. The belt is 9 years old and has 85000 miles on it.