My Lights Dim Also

Rich Dotterer · February 25, 2011

Hello Guys

I am New Here

I have been searching for answers I am Having with my 08 Sierra

I have the 4.8 V8 with 36K on it

I have been seeing my Lights also dimming when I push the Brake Pedal

I have other Issues I wanted to post some questions here to see if you guys could help me figure out what's going on with my Truck

I installed a LED Tail Gate Bar recently and noticed that a couple times that it was lit up when the truck was not running and the Key was off

I have had to replace the Brake Light switch under the Dash because it was not letting my Remote starter start the truck and I took the truck back to the Aftermarket shop and the thing worked when I got there but as soon as I went to start it the next day it was doiung it all over again

The Bigger Issue I am having for the last 1.5 years is the Volt Meter in the Dash has these weird readings

I will be driving down the road and a normal reading with be over 14 Volts then suddenly the Volt Meter will go way below 14 Volts and the windshield wipers and windows will operate very slowly even at 70 Mph. & 2,100 RPM's

I usually have to stop and shut the truck off & restart it to get the eter to read over 14 again and within a minute or so it'll go right back down below 14 volts and the same scenario will happen all over again

On Christmas Eve I went to Auto Zone and had then test the Charging system and they got a spike reading when I put a Load on the system with the RPM's at 2,000 as insdtructed

I changed the Delco Alternator & the Battery the Same Day and I am still having this Issue with the Meter in the Dash Droppiung way Below 14 Volts

Have you Guys ever Heard anything Like this Issue

Any HELP would be appreciated because after several trips to the Dealer this Problem still is not resolved and it's bugging the *$*&%$*& outta me

Any Help would be Extremely appreciated

Thanks

Rich Dotterer

Sch'dy New York....

Zed-Seventy-One · February 25, 2011

When cruising I believe the trucks with drop the voltage to around 12, fuel savings.

knightr · February 25, 2011

The computer will adjust the alternator volts according to the demand & state of battery charge.

The alternator is a huge drag on the engine when outputing 14 volts compared to 12 volts.

The days of the voltmeter being glued in one position are gone. The new way works quite well &

will save U gas in the process.

Read your owners manual, as it explains how the charging system works.

#07-06-03-009B: Information on Voltmeter Gauge Fluctuation Due to Regulated Voltage Control System

Voltmeter Fluctuation Condition

Some customers may comment that the voltmeter is fluctuating between 12 and 14 volts on their full size pickup or utility vehicle. Starting with the 2005 model year, light duty full size pickups and utilities are equipped with a Regulated Voltage Control (RVC) system. This system reduces the targeted output of the generator to 12.6-13.1 volts when in "Fuel Economy Mode" to improve fuel economy. The generator may exit "Fuel Economy Mode" if additional voltage is required. This will cause the voltmeter to fluctuate between 12 and 14 volts as opposed to non-regulated systems that usually maintain a more consistent reading of 14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should be attempted.

700 sportsman · February 25, 2011

Not sure if it's a similar/related issue. But my dad's truck, along with several others I've seen have had ground issues. In some cases it totally caused the truck to go limp, and sometimes once the vehicle was locked everything went black instantly and wouldn't come on. The key had to be used to open the door to get into the engine compartment. It happened once while we were at lowe's and I touched the ground wire and boom everything fired up and was fine, so that's what led us to the ground. Also sometimes you could tell when you hit the brakes or turned the headlights on you could see the other lights dim as well, however the voltages did stay normal.

We replaced the ground terminal at the battery and everything has been fine for about 3 months now. Some of the other people have also talked their dealer out of a whole new ground harness.

I don't know if it is your particular problem, but it may be worth a shot?

Sir Dan · February 25, 2011

The new variable output alternators are great except they are really hard on our lead cell batteries which like a constant state of charging. Lots of them are only lasting 2 and 3 years now when 5 to 7 was the norm before.

Rich Dotterer · July 2, 2011

The computer will adjust the alternator volts according to the demand & state of battery charge.
The alternator is a huge drag on the engine when outputing 14 volts compared to 12 volts.

The days of the voltmeter being glued in one position are gone. The new way works quite well &

will save U gas in the process.

Read your owners manual, as it explains how the charging system works.

#07-06-03-009B: Information on Voltmeter Gauge Fluctuation Due to Regulated Voltage Control System

Voltmeter Fluctuation Condition

Some customers may comment that the voltmeter is fluctuating between 12 and 14 volts on their full size pickup or utility vehicle. Starting with the 2005 model year, light duty full size pickups and utilities are equipped with a Regulated Voltage Control (RVC) system. This system reduces the targeted output of the generator to 12.6-13.1 volts when in "Fuel Economy Mode" to improve fuel economy. The generator may exit "Fuel Economy Mode" if additional voltage is required. This will cause the voltmeter to fluctuate between 12 and 14 volts as opposed to non-regulated systems that usually maintain a more consistent reading of 14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should be attempted.

Thanks Very Much for your Answer

I was at it all over again this past week because

I just Picked up a Brand New 2011 GMC Flex Fuel Sierra 4X4 with the Vortec V8

about 10 days ago

I was backing into a Parking spot at work, and went to put up the windows and they were going slow, I looked at the Volt Meter and there it was again

The Meter was reading about 12 Volts, and I almost crapped myself thinking I had the Same Problem (or so I thought) as I did with the 2008 GMC I just traded in.

This brought me to a state of Holey Crap because I just got a Loan for 35K for this new truck.

GasHog369 · July 3, 2011

Do the "Big 3 upgrade"..

All vehicles from the factory come with way to small of wiring to properly and quickly get the power from the alternator to the battery , and also to ground it out..

I just had the Big 3 done on mine and notice an immediate difference!

Big 3 consists of upgrading the power wire from alt to battery , the ground wire from engine block to frame, and negative batt to frame.

Usually between 4 gauge and 0 gauge is used. I chose 0 gauge as my shop hooked me up with a great deal.

Once in a while i still notice a dim light or 2 in the interior if i am rolling up the windows at same time, but headlights never dim anymore.

To truly stop any and all light dimming you would need to change every wire in the truck , all harnesses. This is not practical. But the big 3 is.

BTW my setup now consists of the big 3, 280 amp alternator thanx to dc power, and odyssey battery. It is one awesome setup

Edit - i see you are not to far away from me.. If u are ever in the buffalo ny area, check out darryls car audio for the electrical upgrade.. They will get you hooked up properly and not broke

tmoney82 · July 4, 2011

Do the "Big 3 upgrade"..

All vehicles from the factory come with way to small of wiring to properly and quickly get the power from the alternator to the battery , and also to ground it out..

I just had the Big 3 done on mine and notice an immediate difference!

Big 3 consists of upgrading the power wire from alt to battery , the ground wire from engine block to frame, and negative batt to frame.

Usually between 4 gauge and 0 gauge is used. I chose 0 gauge as my shop hooked me up with a great deal.

Once in a while i still notice a dim light or 2 in the interior if i am rolling up the windows at same time, but headlights never dim anymore.

To truly stop any and all light dimming you would need to change every wire in the truck , all harnesses. This is not practical. But the big 3 is.

BTW my setup now consists of the big 3, 280 amp alternator thanx to dc power, and odyssey battery. It is one awesome setup

Edit - i see you are not to far away from me.. If u are ever in the buffalo ny area, check out darryls car audio for the electrical upgrade.. They will get you hooked up properly and not broke

Okay, I got a question. I've having the same problem and I change my negative cable out with a 4 awg cable. Since I will be add a system to my truck, I also ran a piece of 1/0 parallel to it. The 4 awg runs through the sensor and the 1/0 outside of the sensor. Will this end up being a problem? T he only reason why I didn't run the 1/0 by itself because it is cca and not full copper.