Has anyone had any issues with the alternator. Mine is acting up. It will show on the gauge at 14 and then drop to 12 and the light will come on in the messege window. This is happening more frequently. I took it to a mechanic and he is telling me it is my computer going bad. The alternator is less than 1 year old. Im thinking of removing it and having it tested. But, my mechanic is possitive that its the computer. He used the diagnostic computer, and that is saying its the computer. Im confused, i thought the alternator should always be putting out voltage, i tested it with a meter and it was reading 0. Just seeing if anyone else has had this same issue? hanks Kyle, ps its a 2001 lb7 auto no mods.

Alternators are regulated to put out the amount of power that the vehicle demands. And that depends on the computer working correctly so the computer can manage the supply/demand of the alternator. Thats about all I know about alternators.

Same symptoms as my alt when it was bad. Replaced it and all is well. Take it out - have it tested

The alternator has an internal regulator that sets charging voltage but it is highly likely that an ECM on the truck controls the field for charging. In other words, the ECM manages the charging system and the alternator does what it is told. I would get a second opinion before doing anything. Modern charging systems are quite complex and difficult to troubleshoot.

I say take it out and have it tested. Cheapest thing you can do to pin point the problem.

my does the same thing when it is warm out or hot under the hood.if it is cold out under 35 degrees it does not do it

The alternator has it own regulator, testing it and getting 0 you must be talking about amperage because if you started it you had to have at least 9.6 volts. If your Mechanic said it is you computor, I would find one that knows something. Testing an alternator is not rocket science. If you have a clamp metre test the amperage after you start it. With a volt metre is should be above 14.0 volts in adout 1 mineute with a volt metre do a voltage drop test from the alternator body to the battery ground post the lead, that tests you ground conections. any more than .1 clean conections. Same for the power side, from the alternator output to the battery post the lead .1 is maximum. If the unit will not crank or cranks slow and has low voltage and the voltage drop tests are good on the starter then if the charging voltage goes up right away the battery is sulfated. If the battery after running for a while with a charging voltage above 14.0 volts and sitting for an hour shows low voltage,11.0 volts, the battery has a bad cell. PLAY SAFE!

the BIG FIX !!!!! it will take 10 minuites to correct or if I do the job 1/2 hr, my generator (alternator) ACTS UP once a year and the following is my fix. On the back of the alternator is a 4 pin plug remove it spray electrical terminal cleaner on the 2 plug ends and wipe with Q TIPS do not use an abrasive, I think the problem is the terminals oxodize, I have been doing this for the last 4 years.

good luck drive safe :)

What jpringle3 said. Find another mechanic that knows something. Computer has nothing to do with alternator.

The alternator on the duramax is turned on by the computer. there are two wires in the plug on the top of the alternator. One is the turn on when it goes high. The other monitors the load on the alternator. You can check to see if it is turning on by checking the voltage in the turn wire it will be around 10 volts. use a digital meter to check it. You can also remove the plug and jumper 12 volts to it and then check the output. I believe the turn on wire is brown but i would have to check.

Man I'm really started to wonder if it its controlled by the ECM. I know on big rigs there is the alternator output wire directly to the starter terminal or batteries then grounded to the frame or whatever. But i pulled an alternator from a new ford F-150 this weekend and it has 2 connectors, 1 has 4 wires I believe and the other has 2.

On highway trucks use very simple alternators in comparison to automotive. Most are stand-alone regulators with no interface to an ECM. All they need is for the engine to be running and the alternator is working.

In general, automotive alternators have complex "smart" regulators which interface with an ECM on the vehicle and are very difficult to troubleshoot for the average person. I don't know what GM uses with the Duramax engines, but being a modern compact dual internal fan style I am guessing it interfaces with an ECM on the vehicle both for turn-on and electrical load management by controlling the field coil and voltage set point. The alternator cannot run on it's own and must receive instructions from the ECM.

There is one recommendation that keeps coming through in this thread... get a second opinion. Hope you get is solved soon and let use know what you found. :)

i am a gm tech and your alt is controlled by the ecm. have seen a few go bad like you are describing. i think the tech is right. you might need an ecm. of course i am not positive because i have not tested it but if the batteries are tested and alt is tested, check all wiring and connections. it is likely the ecm. gm has a test box to put between the alt and the ecm. it test the alt and the ecm. it will tell you which one is at fault.

I fixed it!!!!, I had a 3 year warranty on the alt. so i had it replaced. But, i also cleaned the plugs as described in other post. The old alt. passed the test, but as i said it was intermittent. Ive had it on for 2 days and no issues. Before the alt. would act up 5-6 times a day. Im glad it was covered and easy. Im sure the ecm is not cheap. Thanks guys. Kyle

But it was the ECM! LOL:rolleyes: