2001 2500HD Charging issue

[AnchorJoe]

Hi everyone,

I have a 2001 2500HD P/U with a charging issue. I recently took a road trip (~100mi) on Thanksgiving, and on the way I happen to notice that my headlights would dim and the heater motor would slow down. At that point, I started watching the charge meter on the dash. When the symptom would show itself, I noticed the charge meter was basically dropping to battery voltage, then it appeared the alternator would kick back on and start charging again. Initially, I was thinking it could be a loose connection since it was sporatic. Upon inspection, I did find the ground cable on my second battery was a little loose so I tightened it down for the return trip home. On the way home, the problem was not as frequent, but it still happened.

Could this be a sign that my alternator is getting ready to go out, or would a bad battery cause this problem? I have not taken a hydrometer to the batteries yet to see if I have a bad cell, so I thought I would post this out here to get some feed back in case I am on the wrong track with my thinking. My wife and I only have the one vehicle right now so I want to replace the right part to keep the truck reliable.

Thanks...

[j cAT]

Originally Posted by AnchorJoe

Hi everyone,

I have a 2001 2500HD P/U with a charging issue. I recently took a road trip (~100mi) on Thanksgiving, and on the way I happen to notice that my headlights would dim and the heater motor would slow down. At that point, I started watching the charge meter on the dash. When the symptom would show itself, I noticed the charge meter was basically dropping to battery voltage, then it appeared the alternator would kick back on and start charging again. Initially, I was thinking it could be a loose connection since it was sporatic. Upon inspection, I did find the ground cable on my second battery was a little loose so I tightened it down for the return trip home. On the way home, the problem was not as frequent, but it still happened.

Could this be a sign that my alternator is getting ready to go out, or would a bad battery cause this problem? I have not taken a hydrometer to the batteries yet to see if I have a bad cell, so I thought I would post this out here to get some feed back in case I am on the wrong track with my thinking. My wife and I only have the one vehicle right now so I want to replace the right part to keep the truck reliable.

Thanks...

my alternator failed at about 128,ooomi, 2000 silverado this yr.

the voltage regulator has circuitry that corrodes then no output. this is now corrected with the new alternators available.[different design] . I got my delphi lifetime new alternator at auto zone , so far good..easy to replace.

the voltage on the dash guage drops to about 12.5volts from 14 volt

[4x4junkie]

it is possiblw with the optional dual battery setup that one battery has a dead cell. the batteries are run parralel to maintain the 12 volt system, if one of the 2 batteries was to have a dead or weak cell it is possible to act in that manner as well. I would unhook the batteries and have them checked before replacing the altornator. In the event both batteries test ok, then i would agree the problem to be the altornator.

[AnchorJoe]

OK, so I had the batteries load tested and both were below 50% rating. Should be ~800CCA and one measured ~400CCA and the other measured ~450CCA. So, I replaced both batteries last night.

Now, a symptom that I am seeing is when I idle down from higher RPM's (1800-2200), I notice that the alternator charge guage drops off to below 14VDC then goes back up to just below the mark in the middle of 14 and 19VDC. I haven't noticed the charging system doing this while I have been driving, just when it idles down near a stop or in a parking lot after rev'ing the engine up a little. Does this sound normal?

My experience on other vehicles is that regardless of engine RPM, the charge stays relatively stable with no change in load. But these HD trucks seem to be a different beast to me, so I am not sure now.

Thanks for any input.

[j cAT]

Originally Posted by AnchorJoe

OK, so I had the batteries load tested and both were below 50% rating. Should be ~800CCA and one measured ~400CCA and the other measured ~450CCA. So, I replaced both batteries last night.

Now, a symptom that I am seeing is when I idle down from higher RPM's (1800-2200), I notice that the alternator charge guage drops off to below 14VDC then goes back up to just below the mark in the middle of 14 and 19VDC. I haven't noticed the charging system doing this while I have been driving, just when it idles down near a stop or in a parking lot after rev'ing the engine up a little. Does this sound normal?

My experience on other vehicles is that regardless of engine RPM, the charge stays relatively stable with no change in load. But these HD trucks seem to be a different beast to me, so I am not sure now.

Thanks for any input.

your batteries were not that bad....
did you have them test out the new batteries ? new means new not good !

the voltage should be 14 volts just over the 14 mark..the voltage should not wander..

at idle with the engine hot measure the volts at battery, then at the alternator..in both cases use the alternator housing for the ground connection..increase load then shut off all loads see how it is holding a solid 14.25 volts...this would be at engine hot air temp 35-55 deg F

[4x4junkie]

normally the speratic reading would lead me to the voltage regulator built into the altornator, however i have a 2000 silverado 2500 LT 4x4 with 6.0 vortec equipped with the optional dual battery installation and it fluctuates between 14 and 16 volts depending on engine rpm ...... i however cannot say this is normal for these trucks ...... but mine has had that fluctuation ever since i bought it.

[j cAT]

Originally Posted by 4x4junkie

normally the speratic reading would lead me to the voltage regulator built into the altornator, however i have a 2000 silverado 2500 LT 4x4 with 6.0 vortec equipped with the optional dual battery installation and it fluctuates between 14 and 16 volts depending on engine rpm ...... i however cannot say this is normal for these trucks ...... but mine has had that fluctuation ever since i bought it.

the only time the voltage will be not at the 14volt region would be when cold start in cold weather..if the temp was 10deg f on the first start at this temp the voltage will be 15.5volts. after the alternator heats up this will drop to the 14 volt area......

on a hot start arizona 115 deg f this voltage may be 13.25volts. this is all about the voltage regulator temperature control...

with a steady operating temp this voltage should not vary with RPM .....if so I would say the diodes are damaged, this would cause a half wave output which will give the alternator a voltage fluctuation with rpm changes.

[AnchorJoe]

Thanks for the replies and great info. I will check the charging at the battery and the alternator with and without loads.

With the new batteries installed and a few days use, the fluctuation does seem to have reduced in count and the system appears to be stabilizing a little. I think after I check the charging system directly, I will monitor it a little more and go from there. I still might just change out the alternator in the end.

Thanks again for the info.

[4x4junkie]

your welcome, keep us posted on what you find out

[AnchorJoe]

OK, so I took the truck down to an autozone to have the charging system tested. Thankfully the system was causing the lights to "pulse" lightly and the guy that tested the system saw it also. Anyway, he checked the batteries (good), checked the cranking power (good), checked the charge (good at the immediate test), then put a small load on the system and even though his little hand held device said pass; he said he saw the lights dim down which he said was not normal.

Long story short, I decided to purchase a new alternator and get that changed out. That will happen tomorrow. My hope is the slight whining the alternator seems to be doing stops as well as the fluctuation. Fingers crossed...

[j cAT]

Originally Posted by AnchorJoe

OK, so I took the truck down to an autozone to have the charging system tested. Thankfully the system was causing the lights to "pulse" lightly and the guy that tested the system saw it also. Anyway, he checked the batteries (good), checked the cranking power (good), checked the charge (good at the immediate test), then put a small load on the system and even though his little hand held device said pass; he said he saw the lights dim down which he said was not normal.

Long story short, I decided to purchase a new alternator and get that changed out. That will happen tomorrow. My hope is the slight whining the alternator seems to be doing stops as well as the fluctuation. Fingers crossed...

your testing at autozone reveals their limitations on accurate testing with the charge/alternator operation.

go / no go lights was what they used ?

If they used a dc amp probe on the alternator output with all electrical loads on , the current output fluctuations on the meter would be very obvious. this would not be correct..

as the rpm is increased ,the frequency of these fluctuations would increase. this is n/g...

just make sure all the engine / body grounds are cleaned and secure..then its the alternator..

[AnchorJoe]

Good News, I purchased a new alternator and got it installed this morning and did a test run. Truck is purring like a kitty and with some running around town this afternoon the gauge didn't move at all. Looks like the charging issue may be resolved.

Now if I could just find the Chiltons manual on the truck so I can investigate some mechanical issues and see the wiring diagram I would be sitting pretty...

Thanks everyone for your help and guidance on this...