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Voltage drop while driving

21K views 22 replies 8 participants last post by  davidgsmit 
#1 ·
Gentleman (and ladies?),

I've been having a rough time figuring out what is wrong with my vehicle. My biggest concern at the moment is the voltage drop that occurs while driving. Occasionally while driving, the voltage in my truck will go from 14.x volts to about 12.5V as soon as I get off the gas. The voltage itself varies from about 14.0-14.4 volts usually, but still isn't very consistent. My biggest concern is stalling while driving, and not having adequate control of my vehicle. It is rarely an issue, but when it does it causes me a great deal of stress. I've been battling this issue for over a year now, but it has gotten bad recently.

About two weeks ago, I replaced the:
Fan clutch
Water pump
Idler pully
Alternator
Serpentine belt
Spark plugs
Battery

I feel like I have adequately done the checkdown for electronic components. The next thing on my list would be to upgrade "The Big 3" but last time I checked all of my connections looked great. The unusual part is how dramatically the voltage drops after I take my foot off the gas, even if the throttle is open just a bit. If there was a parasitic draw somehow correlated to my engine, I imagine it having to pull some serious amperage (or prevent the charging system to do its job) to affect my voltage that badly while driving.

Additionally, I've had my truck stall on me at a few red lights. It seems to be worse during warm weather as well, but that may be confounded with something else.

Any ideas or help is much appreciated. You guys seem to know your stuff.
 
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#3 ·
The only code I have ever thrown was a P0128 for a faulty thermostat. I replaced that as well (forgot to mention it on the list, along with a coolant flush and fill.)

The problem seems to always be lurking there. But the few times I've actually stalled, it has always been at a red light. When it happens while stopped, I notice my voltage dropping below 14v and the car idling heavy. In the worst instances, it affects my RPMs at idle to the point where it can stall. Also, any additional load on the car (power windows, seat heater, sun roof, blower motor) puts an enormous load on the system to the point where the voltmeter registers significant change.

Hey, thanks for the quick reply!
 
#8 ·
Just so you know I changed out my alt. 3 times with a reman from autozone. They tested the alt and said it was good, but the 4th time I paid more and got a new unit and its been fine for over a year. The 3rd reman unit seemed to be working out but the lights would pulsate. Changed for a new one and it was fixed.
 
#11 ·
My old one only had 60k on it and I just paid $200 for a new one. I really didn't even want to swap alternators because GM is known for their long-life alts and I didn't want to think it was even close to going.

The idea of going through 4 alternators makes me cringe. I'm thinking I might just take apart the old one and see if I can clean it up, maybe resolder some connections. The more and more I think about it, I am compelled to think the problem is somewhere from the alternator to the battery, or my grounds.
 
#9 ·
Gentleman (and ladies?),

About two weeks ago, I replaced the:
Fan clutch
Water pump
Idler pully
Alternator
Serpentine belt
Spark plugs
Battery

I feel like I have adequately done the checkdown for electronic components. The next thing on my list would be to upgrade "The Big 3" but last time I checked all of my connections looked great. The unusual part is how dramatically the voltage drops after I take my foot off the gas, even if the throttle is open just a bit. If there was a parasitic draw somehow correlated to my engine, I imagine it having to pull some serious amperage (or prevent the charging system to do its job) to affect my voltage that badly while driving.

Additionally, I've had my truck stall on me at a few red lights. It seems to be worse during warm weather as well, but that may be confounded with something else.
...But the few times I've actually stalled, it has always been at a red light. When it happens while stopped, I notice my voltage dropping below 14v and the car idling heavy. In the worst instances, it affects my RPMs at idle to the point where it can stall. Also, any additional load on the car (power windows, seat heater, sun roof, blower motor) puts an enormous load on the system to the point where the voltmeter registers significant change.
Have you cleaned your throttle body at all? I'm not sure if that would effect you as much while the truck is in motion, but when sitting idle, with your AC/heat on and having RPM/stalling issues is one of the tell tale signs of a dirty throttle body with our I6 engines, especially post battery replacement since your PCM will reset and be using parameters for a clean throttle body. If you haven't done it recently, it may be worth it just cuz it's pretty cheap to do. :m2:
 
#10 ·
I sprayed it down and wiped it real quick when I had my resonator off when doing the plugs. I only got the front of it good. Maybe I'll actually take it off this time. Definitely cheap, easy, and worthwhile. I'll take you up on that. Thank you.
 
#14 ·
Have you cleaned your throttle body at all? I'm not sure if that would effect you as much while the truck is in motion, but when sitting idle, with your AC/heat on and having RPM/stalling issues is one of the tell tale signs of a dirty throttle body with our I6 engines, especially post battery replacement since your PCM will reset and be using parameters for a clean throttle body. If you haven't done it recently, it may be worth it just cuz it's pretty cheap to do. :m2:
Okay so I cleaned the throttle body thoroughly today. As of right now, everything seems to be running pretty smooth. It definitely seems to have helped some but I won't know until I drive it.

While I'm covered in grease, I'm gonna upgrade some wires and check some harnesses as suggested by Ralph T. I appreciate all of suggestions you fellow TrailVoys have given. Much respect.

I've attached some pictures of the front/back of my throttle body. You can tell the side I cleaned off when I had the resonator off versus the back end. Definitely used a decent amount of throttle body cleaner.
 

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#15 · (Edited)
So to revive my thread...

I was driving back from school the other day and just got off the interstate. Stopped at a relatively busy intersection and noticed my voltage was at about 12 volts and immediately panicked. I put by foot on the brake and revved my engine some hoping to spool up the alternator but nothing happened. I noticed steam pouring out of my engine. Once the light turned green, I started driving and I could hear my belt squeeling. I pulled over into a Carquest parking lot right down the road and popped the hood. I had coolant everywhere in my engine compartment - it was an absolute mess.

I had to have my car towed to the mechanic because I'm so pressed for time lately. I wasn't sure if my water pump seized or if I blew a head gasket. My money was on the water pump because I was the one who replaced it. My mechanic called me today confirming that my water pump did in fact fail. He is going to save it for me so I can look at it and bring it back to Autozone. I also need a new belt and a full thing of coolant. Now my simple $70 DIY job is going to cost me a nice chunk of change because of a ****ty Duralast water pump. I'm hoping this fixes some of my problems. I will post an update when I get everything back.
 
#16 ·
Happy Easter

So... I got my car back from the mechanic... BRAND NEW water pump seized... a solid $350. Luckily I have a NAPA pump in instead of the Duralast ones. Jeez.

So I'm driving with the girlfriend, and my voltage is still going crazy. Not often like always, but it still happens. I am absolutely stumped. I just ordered 8ft of Streetwires 4AWG wire, some terminal connectors, and some sideposts for the battery. I upgraded my V- to ground but I want to make sure I do it the right way.

I throw no codes and everything seems to be wired up properly (except for that eery red wire for the trailer.) I so badly do not want to take it to mechanic, especially after seeing how much a $60 job cost me. Any other things to check? My mind is blown.
 
#17 ·
voltage drop

I've had the same issue with my 05 Trailblazer. I'll be driving and i notice my votlage drop. It's not as significant as yoiurs but it drops down to 12. I've stalled a few times when i've been stopped. If you replace your alernater and it fixes it please post it work. I'm a college student and can't afford to try a lot of fixes
 
#19 ·
I've had the same issue with my 05 Trailblazer. I'll be driving and i notice my votlage drop. It's not as significant as yoiurs but it drops down to 12. I've stalled a few times when i've been stopped. If you replace your alernater and it fixes it please post it work. I'm a college student and can't afford to try a lot of fixes
Danny,

Sorry I didn't get to you sooner. Just moved into a new apartment and didn't have internet.

I have replaced the alternator as I have previously mentioned. This did not stop the problem, but the voltage drop is not as significant now. I still have the problem, but I have not stalled in some time. Recently, I have noticed the voltage jumping around a bit and the car seeming to idle a little heavy but it still remains above 14v. Rarely, the voltage drops and I notice my lights dim.

I have a few questions for you if you don't mind: I notice my car chirps on the driver side front intermittently but I cannot locate the sound. I thought it was my suspension, but I passed inspection and just had a wheel bearing replaced. Do you also have this problem? The only pulley component I have yet to replace is the A/C compressor.

Also, I notice my SES light flash on me sometimes, but it does not stay on and I cannot capture the OBDII code. Have you noticed this?

My ABS is also firing when I am driving slow. This is recent and I am confident it is unrelated. I figured I would mention it in case you had a similar issue.

I'm in college too buddy and I feel your pain. I'll try to help with whatever I can.

Thanks,
Mike
 
#22 ·
I havn't notice any chirping from my front at all. The only thing i've notce is that my truck likes to idel hard. I only have 87,000 mile on it. I can notice the voltage drop more at night when my head lights are on. When my truch has stalled was during the day when my head lighst were off. I put on after market hid lights. I was thinking about cleaning my air intake valve to see if that would help. Since i got the truck two years ago i've replace the thermostat, installed a new air blower sensor pack, my fuel sensor has been out for a year in a half. I love the truck but i wished it was better built or chevy would rembuirse us for the frustration.
 
#23 ·
Pretty sure I know why you're having this problem...

This subject has been talked about a number of times on this forum.

From what I've learned, and experienced on my own TB;

There's an air pump that's attached to the frame of the vehicle directly under the driver's seat. This air pump performs a self-check every time you start the vehicle. I believe it takes about 15-20 seconds for it to shut off after starting your engine (you can hear it if you listen for it).
If you drive away without letting the pump finish its check, it'll screw with the voltage of your TB. I can't tell you with 100% certainty that this is really the culprit, but what I can tell you is that I've never had my lights flicker or voltage drop after letting the pump finish its test (although that only consists of about 10 night drives)

I've done a lot of reading up on this topic and it seems there simply is not a solution for this problem other than to purchase a high end battery (glass mat type) that's designed for high voltage applications such as stereo amps. Sears actually sells the best car batteries on the market, but you have to get the DieHard Platinum which runs about $200. Fortunately it also has a 3 year warranty for that price. Note: that's about the only thing I'd ever buy at Sears... especially from their automotive department! I used to work there!

I don't have a high end battery myself, but from what I've read other people have found this to solve their problems as the higher end battery is capable of evening out the voltage swings whereas your typical battery isn't. I simply don't have the funds to try it with all the other things I'm always fixing on my TB!!! Maybe some day my TB will give me more than a month of trouble free driving; until then I'll just have to have flickering headlights.

One other thing: GM is aware of the problem and claims it's "normal". At least you don't have to pay extra for the disco lights feature!

Hope this helps! Good luck and don't forget to buy a Jap next time!
 
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