Alt Gauge

[5829BMG]

New here, Hi everyone. I'll start by saying I've owned GMC trucks all my life and I love'em and never had any real problems with any of them.But I just bought a new 09 Sierra crew cab 4x4 and it has 1400 miles on it. The first 500 miles I did not notice any thing weird and the alt showed 14+ but after that the alt gauge goes down below the 14 mark almost dead between the 9 and 14 after it warms up.At every start up 14+ then slowly goes down to i'd say 12. Logic tells me this isnt right. took to the dealer and was told no codes,no problem. All the trucks i've ever had the gauge is never below the 13on the older gauges. Any body run into this?

[pwall]

Mines doesn't seem to move at all......however, difference trucks really.

However, I seem to recall that even in my '02 YukonXL it didn't move that much either.

 

And welcome btw!

[thearborbarber]

It's normal. My 2009 gmc does it as well. I was reading a mechanics magazine while getting my oil changed and there was an article in it about clutched alternators. It seems automakers are squeezing the last bit of mileage out of cars by having a clutch on the alternator. It disengages when there is no electrical load.

[5829BMG]

It's normal. My 2009 gmc does it as well. I was reading a mechanics magazine while getting my oil changed and there was an article in it about clutched alternators. It seems automakers are squeezing the last bit of mileage out of cars by having a clutch on the alternator. It disengages when there is no electrical load.

 

 

Well that would explain why, but it makes me nervous.I wonder if it could be replaced with a non-clutched one.I want to upgrade my audio but worried about how it would hold up.

[Jsdirt]

As far as I know GM doesn't use a clutch on the alternator, but has a microprocessor controlled voltage regulator. If it senses that the battery is fully charged, it cuts voltage to the electromagnetic rotor inside the alternator, which basically does the same thing as disengaging a clutch - reduces the load on the engine. When the alternator is sensing a fully charged battery, your volt gauge will read battery voltage. It's basically an "on-demand" alternator.

[5829BMG]

As far as I know GM doesn't use a clutch on the alternator, but has a microprocessor controlled voltage regulator. If it senses that the battery is fully charged, it cuts voltage to the electromagnetic rotor inside the alternator, which basically does the same thing as disengaging a clutch - reduces the load on the engine. When the alternator is sensing a fully charged battery, your volt gauge will read battery voltage. It's basically an "on-demand" alternator.

[5829BMG]

As far as I know GM doesn't use a clutch on the alternator, but has a microprocessor controlled voltage regulator. If it senses that the battery is fully charged, it cuts voltage to the electromagnetic rotor inside the alternator, which basically does the same thing as disengaging a clutch - reduces the load on the engine. When the alternator is sensing a fully charged battery, your volt gauge will read battery voltage. It's basically an "on-demand" alternator.

 

 

That makes even more sense, the more I thought about it didnt see how a mech clutch would be possible.I'm more old school when it comes to alt's.

[suzannehanlon]

The kids and I went on a short road trip this summer. Needless to say, the game cube came too! They had a 75W inverter plugged in to the rear entertainment unit. The voltage was down and stayed down, what seemed to be a long time. During the course of the trip, the altenator kicked in and out and the voltage came up and went down. I did however have the dealer check it out! Again, no codes, no nothing, no problem, and 1/2 service bill!

 

It's normal. My 2009 gmc does it as well. I was reading a mechanics magazine while getting my oil changed and there was an article in it about clutched alternators. It seems automakers are squeezing the last bit of mileage out of cars by having a clutch on the alternator. It disengages when there is no electrical load.

 

 

Well that would explain why, but it makes me nervous.I wonder if it could be replaced with a non-clutched one.I want to upgrade my audio but worried about how it would hold up.

 

[pm26]

Even my '06 truck has this feature. During the recent long trip I would say that the alternator charging voltage was at 12 something Volts for about 2/3 of the trip. Remember that the alternator voltage must be above the battery voltage for the alternator to charge the battery.

When charging, the alternator voltage jumps to about 14.5 Volts.

[RickMN]

I think Jsdirt is right about not having a decoupler on this truck.

 

Instead I think you might have the RVC system.

 

Here's a link to an article about fluctuating voltages on GM trucks

 

Voltmeter fluctuates on GM truck