Tahoe Voltage drop


bass_caster
02-03-2009, 01:52 PM
2000 Tahoe N/B
5.3l
4x4

while driving, my tahoe experiences a voltage drop at various times. i only notice it at night while head lights are on. the headlights and any interior lights that might be on, get noticably dimmer as well as heat - a/c blower has a noticable drop in fan speed. it usually last 2-3 seconds then jumps back up to normal. sometimes it happens 3-4 times during a longer drive (hour or more) and sometimes it doesn't happen for weeks at a time. the drop is also displayed on the instrument panel volt meter (just under 14v is normal range and it drops down to 9-10v. it can happen at any engine speed from idle, to cruising speeds at 2000rpm.

i had it at the dealer for some warranty work and they said there was a service bulletin about the plug that goes directly into the alternator. i ordered a new plug and a service tech at the dealership was nice enough to install the new plug at no charge while i was parked in their lot. unfortunately, it didnt fix the issue. i don't have any dead battery/non charging type issues at this point. everything is stock in the truck except the silver star headlight bulbs and an after market stereo/head unit. it doesnt suck a huge amount of juice since theres no amps or anything like that.

i bought the truck new and didnt have the issue for quite some time. i think it started maybe 2 years ago.

can it be the alternator itself?

also, whatever the cause, why would it be so intermitent? it seems to happen for no reason. if it happened when i turned on a light or stereo or something, it would almost be understandable.

j cAT
02-03-2009, 07:47 PM
2000 Tahoe N/B
5.3l
4x4

while driving, my tahoe experiences a voltage drop at various times. i only notice it at night while head lights are on. the headlights and any interior lights that might be on, get noticably dimmer as well as heat - a/c blower has a noticable drop in fan speed. it usually last 2-3 seconds then jumps back up to normal. sometimes it happens 3-4 times during a longer drive (hour or more) and sometimes it doesn't happen for weeks at a time. the drop is also displayed on the instrument panel volt meter (just under 14v is normal range and it drops down to 9-10v. it can happen at any engine speed from idle, to cruising speeds at 2000rpm.

i had it at the dealer for some warranty work and they said there was a service bulletin about the plug that goes directly into the alternator. i ordered a new plug and a service tech at the dealership was nice enough to install the new plug at no charge while i was parked in their lot. unfortunately, it didnt fix the issue. i don't have any dead battery/non charging type issues at this point. everything is stock in the truck except the silver star headlight bulbs and an after market stereo/head unit. it doesnt suck a huge amount of juice since theres no amps or anything like that.

i bought the truck new and didnt have the issue for quite some time. i think it started maybe 2 years ago.

can it be the alternator itself?

also, whatever the cause, why would it be so intermitent? it seems to happen for no reason. if it happened when i turned on a light or stereo or something, it would almost be understandable.

the dealership is the worst place to go...change parts and lets guess by using the TSB'S instead of eyes, test equiptment, and brains...

since this is a problem of a couple of years now all grounds must be checked...remove neg battery terminal then clean all grounds and also the positive connections...including the alternator in the engine compartment/and engine...

LVN-M99
03-12-2009, 06:07 PM
2000 Tahoe N/B
5.3l
4x4

while driving, my tahoe experiences a voltage drop at various times. i only notice it at night while head lights are on. the headlights and any interior lights that might be on, get noticably dimmer as well as heat - a/c blower has a noticable drop in fan speed. it usually last 2-3 seconds then jumps back up to normal. sometimes it happens 3-4 times during a longer drive (hour or more) and sometimes it doesn't happen for weeks at a time. the drop is also displayed on the instrument panel volt meter (just under 14v is normal range and it drops down to 9-10v. it can happen at any engine speed from idle, to cruising speeds at 2000rpm.

i had it at the dealer for some warranty work and they said there was a service bulletin about the plug that goes directly into the alternator. i ordered a new plug and a service tech at the dealership was nice enough to install the new plug at no charge while i was parked in their lot. unfortunately, it didnt fix the issue. i don't have any dead battery/non charging type issues at this point. everything is stock in the truck except the silver star headlight bulbs and an after market stereo/head unit. it doesnt suck a huge amount of juice since theres no amps or anything like that.

i bought the truck new and didnt have the issue for quite some time. i think it started maybe 2 years ago.

can it be the alternator itself?

also, whatever the cause, why would it be so intermitent? it seems to happen for no reason. if it happened when i turned on a light or stereo or something, it would almost be understandable.
I have got the exact same problem with my 99 Tahoe 2dr ,same fadeing,same voltage drop .The truck runs great even while the problem is occuring,I thought it was a wet weather problem with a short or something (being from the west coast of canada and all) but it dosen't matter. I had my alternator swapped out and that didn't make a difference. I even get a buzz in my radio in time with my exceleration. I'll try grounds as well good luck.

j cAT
03-13-2009, 09:38 AM
I have got the exact same problem with my 99 Tahoe 2dr ,same fadeing,same voltage drop .The truck runs great even while the problem is occuring,I thought it was a wet weather problem with a short or something (being from the west coast of canada and all) but it dosen't matter. I had my alternator swapped out and that didn't make a difference. I even get a buzz in my radio in time with my exceleration. I'll try grounds as well good luck.

let us know how you made out /what you found...
the other guy never let us know how it was resolved...

RahX
03-13-2009, 07:57 PM
the dealership is the worst place to go...change parts and lets guess by using the TSB'S instead of eyes, test equiptment, and brains...

since this is a problem of a couple of years now all grounds must be checked...remove neg battery terminal then clean all grounds and also the positive connections...including the alternator in the engine compartment/and engine...

It's not the dealership, it's the people. Some people are money hungry and could care less. If there is a problem and you're paying to have it fixed it should be fixed no matter where you take it. A lot of times the dealership is the best place to take it because it may be a common/known problem that a lot of independent places won't know about even with access to stuff like Alldata (must give props to alldata, they have about 90% of the stuff that Subaru, Mitsubishi, Kia and Dodge have on the factory websites). Even past that, they have access to a service tech line they can call and talk to someone who has access to common problems and random fixes to weird things you wouldn't have much luck figuring out on your own.

Now, as jcat said, definitely check grounds. Make sure your cables are good and not corroded. Also, have you ever changed the battery? You might have an alternator with a fairly intermittant problem. Even if you had it tested, they might not find it is bad. About the only way to test for a bad alternator is to replace the thing unfortunately. I did find a bulletin related to this problem which basically says a good battery can handle load/unload better and less noticeably than a weak battery.

INFORMATION

Bulletin No.: 02-06-03-008D

Date: July 21, 2008
Subject:
Low Voltage Display on IP Gauge, Lights Dim at Stop Lights, Battery Discharged, No Start, Slow Cranking, Dim Lights at Idle, Low Generator Output

Models:
1990-2009 GM Passenger Cars and Light Duty Trucks (including Saturn)
2003-2009 HUMMER H2, H3
2005-2009 Saab 9-7X

Supercede:

This bulletin is being revised to add the 2009 model year. Please discard Corporate Bulletin Number 02-06-03-008C (Section 06 - Engine).

Any vehicle may have a low voltage display (if equipped with gauges), lights that dim at stop lights, slow cranking, no start, low generator output at idle or dim lights at idle when electrical loads are heavy at idle or under slow driving or infrequent usage conditions. These characteristics may be more noticeable with customer added electrical accessories, or with a discharged battery. These are normal operating characteristics of a vehicle electrical system and no repairs should be attempted unless a proven fault has been diagnosed.

During normal driving conditions, when engine speed is above 1000 RPM, the generator is designed to do two things:
^ Supply the current necessary to operate the vehicle's originally equipped electrical devices (loads).

^ Recharge/maintain the battery's state of charge.

The following factors may affect generator and battery performance:
^ Non-usage of the vehicle for extended periods of time. The vehicle's computers, clocks and the like will cause the battery state of charge to drop (For example; 30 days in a parking lot and the vehicle may not start because of a dead battery or a vehicle which is driven only a short distance once a week may end up with a discharged battery to the point where the vehicle may not start). This would be considered abnormal usage of the vehicle and the normally expected result for the vehicle battery, generator and electrical systems.


^ At idle, vehicle electrical loads may exceed the low speed current (amperage) output of the generator and when this happens the shortfall comes from the battery. This will result in a drop in the electrical system voltage as the battery delivers the additional electrical current to meet the demand. This is equivalent to the brown outs experienced by homes and businesses when the electrical demand is more than the supply. See Figure 1.

^ Extended periods of engine idling, with high electrical loads, may result in a discharged battery. Attempting to recharge a battery by letting the engine run at idle may not be beneficial unless all electrical loads are turned "OFF".

^ Increased internal generator temperatures from extended idling can also contribute to lower electrical system voltage. As the generator's internal temperature rises, the generator's output capability is reduced due to increased electrical resistance.



Some typical examples of electrical loads are shown above.

Depending on the vehicle application, generator current (amperage) output at engine idle speeds of 600-700 RPM can be as low as 35 percent of the full rated output. With enough electrical loads "ON", it is easy to exceed the generator current (amperage) output when the engine is at an idle of 600-700 RPM. This is a normal condition. The battery supplements for short periods of time. Items that affect the vehicle's electrical system current and voltage at idle are the number of electrical loads being used, including add-on accessories, and extended idle times. When the vehicle speed is above approximately 24 km/h (15 mph), the engine/generator RPM is high enough and the generator current (amperage) output is sufficient to supply the current (amperage) requirements of the vehicle as originally equipped and recharge the battery.

Dimming lights at idle may be considered normal for two reasons:
1. As the engine/generator speed changes, so will the current (amperage) output of the generator. As a vehicle slows, engine/generator RPM slows and the current (amperage) output of the generator may not be sufficient to supply the loads, the vehicle system voltage will drop and the lights will dim. Dimming of the lights is an indication that current is being pulled from the battery. If the battery is in a low state-of-charge (discharged condition), the driver will notice a more pronounced dimming than a vehicle with a fully charged battery.

2. When high current loads (blower, rear defogger, headlamps, cooling fan, heated seats, power seats, electric "AIR" pump, or power windows) are operating or cycled "ON", the generator's voltage regulator can delay the rise in output. This effect, usually at lower engine speeds, can take up to ten seconds to ramp up the generator output. This is done to avoid loading the engine severely. To increase current (amperage) output, additional torque is consumed by the generator. The engine computer (ECM/PCM) will ramp up engine/generator speed in small steps so engine speed variations are not noticeable to the driver.

For diagnosis of the battery and/or the generator, refer to the appropriate Service Information (SI) or Corporate Bulletin Number 05-06-03-002C.

j cAT
03-14-2009, 09:27 AM
[quote=RahX;5934272]It's not the dealership, it's the people. Some people are money hungry and could care less.quote]

dealerships are in the business of making money...these forums have many a unhappy member with the lies, and excessive charges...also doing poor work...

with any vehicle this TSB would apply, if the vehicle , with an infrequent light dimming..

when your vehicle continuosly dims, and this occurs after many years of no diming, its time to find out why, before its total failure..

then you must also consider the side effects of running on the lower voltage...

with proper testing this is a very easy problemto solve, just takes time....so how much can the dealer charge to clean the ground connections ? how much will he profit ?

so they just jack the bill up by replacing parts...
unless its on warrantee repair...

RahX
03-14-2009, 09:53 AM
Everybody is in the buisiness of making money, that is why the USA is a CAPTIALIST nation, if we can't make money at something then we probably won't have much incentive to do it for long. I work at a dealership and I can tell you 100% from personal experience, a good dealership won't screw you around. If we charge you an hour for diag, you get your hour and more. We get it figured out so when it comes to getting the thing fixed out of warranty, that hour of diag works as a credit towards the repair. If it is something we cannot duplicate, we try to have the customer duplicate it for us. If that doesn't work they get charged 1/2 labor for an hour and if the vehicle acts up and they can get it to us while it is doing it, we check it out then and there. So i'd recommend you stop trying to down dealerships. Every dealership is different and if you've had a bad experience at one and did not talk to the service manager then don't go back. Most of the time if something wasn't fixed right or to your satisfaction a talk with the service manager about the problem will get you somewhere. They can do good will warranty work if they like you too.

j cAT
03-14-2009, 07:39 PM
Everybody is in the buisiness of making money, that is why the USA is a CAPTIALIST nation, if we can't make money at something then we probably won't have much incentive to do it for long. I work at a dealership and I can tell you 100% from personal experience, a good dealership won't screw you around. If we charge you an hour for diag, you get your hour and more. We get it figured out so when it comes to getting the thing fixed out of warranty, that hour of diag works as a credit towards the repair. If it is something we cannot duplicate, we try to have the customer duplicate it for us. If that doesn't work they get charged 1/2 labor for an hour and if the vehicle acts up and they can get it to us while it is doing it, we check it out then and there. So i'd recommend you stop trying to down dealerships. Every dealership is different and if you've had a bad experience at one and did not talk to the service manager then don't go back. Most of the time if something wasn't fixed right or to your satisfaction a talk with the service manager about the problem will get you somewhere. They can do good will warranty work if they like you too.

It sounds as though you work for a dealership that is concerned for the customers satisfaction,,,,you will most likely not suffer when the 1,000 or so GM dealerships go...

this is not the norm..I have seen and experienced much illegal and false acts at the dealership....these places are not where good honest people should work...

I will not miss the GM screw the customer attitude.....

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