Battery or electrical.

[Dan2002]

2002 GMC Denali

I recently found an issue with my vehicle

The past 3 days I have been driving at high speeds. I noticed when acelerating hard the battery volts gauge drops. And the lights on dash start flickering. The radio turns on and off. Battery light comes on.

After a stop or red light. The volt gauge comes back up to normal and all light stop flickering.

I thought maybe my battery is no good.

Well yesterday when driving back home. It started to do the same but this time the light and all dash components stopped working. After driving around 4 minutes. It started to lose power eventually driving about 10MPH. The dash showed "reduced engine power".

I managed to make it home. After waiting about 10 minutes. I decided to give it a look and started it and drove it around the block with no problems.

It seems that I lose voltage going at high speeds 60MPH +

 

[iamdub]

So, did you replace the battery? Does it happen if you rev it in neutral? Just trying to determine if it's RPM- or load-based. My first suspicion is failing alternator or even the belt slipping at higher RPM.

 

[Doubeleive]

if you have a autozone near you they will check your battery and alternator for free, I would also check for a bad ground

 

[Martinjmpr]

I would suspect the alternator or a bad connection. As ^^^ said above, it's easy to get both the battery and alternator checked at any auto parts place. If your alternator is bad you can replaced it in about 1/2 hour or less with basic hand tools.

 

[915_Tahoe]

I would suspect the alternator or a bad connection. As ^^^ said above, it's easy to get both the battery and alternator checked at any auto parts place. If your alternator is bad you can replaced it in about 1/2 hour or less with basic hand tools.

I SECOND MARTINJMPR, I DOES SOUND LIKE A ALTERNATOR PROBLEM.

 

[adriver]

Your alternator just keeps your battery charged, while your electronics are run off the battery. Yes, I know It theoretically will run your system, but that's not how its supposed to work. If your alternator fails, your system just runs off your battery and drains it until it dies. I'm not saying it couldn't be the pulley, but I don't think its the electrical aspect of the alternator; unless someone knows if maybe a diode went bad, causing a surge or voltage fluctuation. I noticed you recently needed to replace your motor mounts, was there any kind of problem with that, (your hard acceleration)? What is your voltage fluctuation? Is this happening at a specific speed or rpm? Can you manually shift lower and get it at the same RPM? I'm thinking its something mechanical, maybe a loose belt tensioner or belt slipping somehow.

 

[06JET]

Had a 98 GMC 3500 once that the battery terminals would corrode every 3 months no matter what I did. When it would happen the connection would get bad and the computer would act crazy. Once the trans stopped shifting and was hung up in 1st. I removed the cables and let the computer reset and everything was fine. My truck would not run off the alt. If the battery completely lost connection the truck would die. It was the times that it would still get a few volts thru a bad connection that screwed everything up.

 

[Dan2002]

Had a 98 GMC 3500 once that the battery terminals would corrode every 3 months no matter what I did. When it would happen the connection would get bad and the computer would act crazy. Once the trans stopped shifting and was hung up in 1st. I removed the cables and let the computer reset and everything was fine. My truck would not run off the alt. If the battery completely lost connection the truck would die. It was the times that it would still get a few volts thru a bad connection that screwed everything up.

I did tried a new battery. But wasn't actually new. It's like 2 month old battery from a 03 suburban. But it was a dead battery. I tried to jump it but my Denali didn't stay running. Maybe it's completely dead. I will get a new battery possibly tomorrow and try it

 

[Matahoe]

More than likely hidden corrosion on the back side of the battery bolts. Once you get both battery cables disconnected you will want to remove both bolts and plastic boots from the cable terminal end. Then you can go town with electrical cleaner and a wire brush.

Also, you can disconnect the alternator single wire (tape it off) and 2 pin harness to rule it out. There isnt any problem running the engine on just the battery.

 

[Dan2002]

I bought a brand new battery and it seems to not have changed at all. Battery boltage on the gauge begins to drop when reaching 2000 rpm's. At night I can see my lights to dim a little bit and if I keep acelerating I get the battery light on the message center screen.

Could it be alternator issue? Or something electrical

 

[Doubeleive]

I would have the alternator tested

 

[shreksbrother]

I bought a brand new battery and it seems to not have changed at all. Battery boltage on the gauge begins to drop when reaching 2000 rpm's. At night I can see my lights to dim a little bit and if I keep acelerating I get the battery light on the message center screen.

Could it be alternator issue? Or something electrical

Have you had the alternator tested as several others have suggested? May have saved you the cost of a new battery...

Sent from my Galaxy Note9 using Tapatalk

 

[Matahoe]

Could it be alternator issue? Or something electrical

Why are you asking this again? I told you how to test it without the alternator...to rule it out.

 

[Martinjmpr]

I bought a brand new battery and it seems to not have changed at all. Battery boltage on the gauge begins to drop when reaching 2000 rpm's. At night I can see my lights to dim a little bit and if I keep acelerating I get the battery light on the message center screen.

Could it be alternator issue? Or something electrical

Nobody here can tell you whether your alternator is bad.

You know who can? Your local auto parts store. Drive there, pull the alternator (it’s a 5 minute job tops) and take it in to have it tested. Even better , if it is the alternator they will almost certainly have one in stock.

Get it done ASAP before you kill that new battery.


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[Matahoe]

Nobody here can tell you whether your alternator.

Rediculous. Sure you can test the alternator at home. If you rule out the wiring and battery. You can test ac ripple and voltage at different rpm's. You can also see amps if you have a clamp meter. There is nothing you cant do at home that a multimeter cant handle. However a pico scope would be ideal.

 

[SmokChsr]

I bought a brand new battery and it seems to not have changed at all.
Could it be alternator issue? Or something electrical

My experience makes me think it's going to a bad connection. I recently had a similar but different problem that I found the cure for by accident. In my case I was getting voltage surges that would reset the dash, and cause all sorts of warnings. (not to mention blow light bulbs). What I think to have found that was causing that was a bad connection in the battery current sensor (not sure what it's actually called but it hangs on the negative lead of the battery).

Once I pulled open that connection and put some DeOxit D100 on each contact and exercised the connection a bit it all stopped. From your symptoms you may be looking at something very similar. So I would try cleaning up those connections and see if you see any change. After that it may be the ECM or connections thereof.

The ECM is the device that controls your alternator and charging voltages, and I'm not sure what all information it's using from the current sensor, but from what I've seen if it's not talking to it correctly it's going to do some bad things.

It also could be a short in the Alternator causing those symptoms, but I don't think it is in this case. The main problem will be that if it is the ECM signals most alternator testers won't differentiate an loss of control from the ECM form a bad alternator.

 

[Dan2002]

Rediculous. Sure you can test the alternator at home. If you rule out the wiring and battery. You can test ac ripple and voltage at different rpm's. You can also see amps if you have a clamp meter. There is nothing you cant do at home that a multimeter cant handle. However a pico scope would be ideal.

Thank you for the help. I recently had time and took out the alternator. Went to Auto part store and got it test it and failed the test. Purchased a brand new one , installed it and no more voltage drop .! Thanks again guys.

 

[SmokChsr]

Thank you for the help. I recently had time and took out the alternator. Went to Auto part store and got it test it and failed the test. Purchased a brand new one , installed it and no more voltage drop .! Thanks again guys.

Well that was a good resolution, and an easy fix. Not many vehicles have an alternator that's as easy to remove and replace as the Tahoe. Also by removing the alternator and testing separately from the vehicle you removed the ECM from the equation.

 

[Doubeleive]