Headlights Flickering maybe resolved

Tcme64 · November 7, 2014

Anyone's opinions would be appreciated. I made a recent post about my headlights flickering on my 2010 Tahoe. My local GM dealer put a new alternator on and checked many other things but did not fix it. My battery is 8 months old. They tested it with their high end tester and it is perfect "BUT" they replaced the battery per GM Tech supports suggestion and the flickering stopped. Makes no sense but time will tell I guess. ANY THOUGHTS?????????????????

newdude · November 7, 2014

Could be a bad cell or had a low health state causing the issue.

Doug_Scott · November 7, 2014

Batteries can create some interesting issues. It used to be a lot easier to diagnose battery issues like this though. When they started sealing the top of the batteries, and then putting that stupid "green eye" in ONE of the six cells, they actually created more issues for mechanics and customers than they fixed. Can't count how many times I have been told by the customer that "the green eye says the battery is good, so why do you say I need a new one?".

The battery has six cells, with each one responsible for approx. 2.2v. If you get one cell that is getting lazy, it may very well pass all the battery tests, but, it will also create some strange issues. Remember that the battery is actually just a large storage and buffer area. Its job is to absorb voltage fluctuations and smooth them out. Looks like yours stop smoothing them out.

terry89460 · January 24, 2016

On my 2005 Trailblazer the Alternator made the lights flicker because the Alternators Regulator was set to high. This was causing the PCM to shut down what is saw as over charge. The regulator should be limiting the voltage to a maximum of 14.5V, this was not happening. The PCM was then taking over by turning off the alternator momentarily to prevent this over voltage level to the battery. If the Alternator Regulator was set properly the PCM would only be a backup protection, as it was intended. I had the PCM doing the regulation ( very poorly) and the regulator in a backup position, backwards from what it should be.

I tried getting an alternator with a lower setting, no luck). So I add a 100A rectifier between the alternator thus lowering the regulated Voltage .8 volts. I used a bridge rectifier and wired with diodes facing both ways. You need a .5 ohm resistor or a diode invert across rectifier to excite the field coil to start charging. This will return the regulation back to the alternator and not the PCM. Looking at posts, this is likely a large problem with GM vehicles that use the PCM controlled alternators.