Voltage Fluctuation
10-08-2007, 09:22 AM
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Voltage Fluctuation
Hi Guys! New Girl here with a quick question.
I have a 1999 Ram with just about 220,000 miles on it that I use to pull my little 2 horse trailer.
Lately I have noticed that my voltmeter has been fluctuating and not just like normal in the morning on cold starts. It actually started about a month ago when we were still seeing daytime temperatures in the 80's so I don't think it is the heater thing that warms the engine up when it is cold.
Oh, I also have a scanner and I was able to read a P1682 code. It said Charging System Voltage Too Low so I replaced the alternator with a brand new one about a week and a half ago. The code hasn't come back, but the voltmeter still moves around. It stays at 14 when driving, but if I stop at a light or park the truck and let it idle for a few minutes it will start to drop.
Does anyone know what might be causing this or if it is normal. I have owned this truck since new and it has never done this before.
Thanks for any help.
Truck Girl
I have a 1999 Ram with just about 220,000 miles on it that I use to pull my little 2 horse trailer.
Lately I have noticed that my voltmeter has been fluctuating and not just like normal in the morning on cold starts. It actually started about a month ago when we were still seeing daytime temperatures in the 80's so I don't think it is the heater thing that warms the engine up when it is cold.
Oh, I also have a scanner and I was able to read a P1682 code. It said Charging System Voltage Too Low so I replaced the alternator with a brand new one about a week and a half ago. The code hasn't come back, but the voltmeter still moves around. It stays at 14 when driving, but if I stop at a light or park the truck and let it idle for a few minutes it will start to drop.
Does anyone know what might be causing this or if it is normal. I have owned this truck since new and it has never done this before.
Thanks for any help.
Truck Girl
10-08-2007, 09:40 AM
#2
Chapter President
Welcome to DTR. I have a 99 and never really notice what the gauge does at a stop, but I'll look at mine and report back. Do you think your grid heater is coming on even after the truck is warm?
10-08-2007, 09:43 AM
#3
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This is your grid heaters cycling on & off when temps are below 50F. Above speeds of 26 MPH it stops. At idle it will / may start up again. Normal, just drive it like you stole it. 
Welcome to DTR
We're glad you are here. This place could use a few more ladies to straighten up the riff raff.
Welcome to DTR
We're glad you are here. This place could use a few more ladies to straighten up the riff raff.
10-08-2007, 10:40 AM
#4
Chapter President
I checked out my gauge and it's rock steady @ a tick over 14. It's warm here today in NC. If the weather is cold I could see the grid heaters coming on, but I've never noticed them coming on after the truck is warmed up. If I shut the truck down at like a drive-thru they will kick on in the winter, which is dumb...
Maybe your IAT sensor is going south?
Maybe your IAT sensor is going south?
10-08-2007, 11:02 AM
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That is exactly what I think is happening. I have a factory service manual and it is my understanding that the heater puts a very large load on the charging system as it cycles. The weather here lately has been pretty cool so I could understand that in the morning, but not after the truck is warm and has been at operating temperature for a while.
It did this even when the temperature was much higher than now too. That is what has me stumped.
10-08-2007, 11:04 AM
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10-08-2007, 11:17 AM
#7
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I would think so, but not sure how bad the sensor would have to get to show a code.
The IAT sensor can get dirty and not read right, usually happens on trucks with exhaust brakes.
Just thowing out some ideas.
The IAT sensor can get dirty and not read right, usually happens on trucks with exhaust brakes.
Just thowing out some ideas.
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10-08-2007, 11:31 AM
#8
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I just wanted to add, I'm going under the assumption that the IAT sensor plays a role with the grid heaters. I know the the IAT sensor plays a part in the high idle and 3 cylinder idle.
10-08-2007, 02:59 PM
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Mike,
High Idle and 3 Cylinder Idle? Is that when the truck revs up on its own when it is cold? I have a friend who has that Smarty thing you have at the bottom of your response and her husband said he activated those for me. Wow, does the truck make some racket when it only runs on half the cylinders.
I always thought the grid heater worked off the temperature sensor behind the grill for the overhead display.
I really don't think my voltage swing is normal, but I just don't know what to do about it now. My batteries are less than two years old and I just replace the alternator. I'm lost.
High Idle and 3 Cylinder Idle? Is that when the truck revs up on its own when it is cold? I have a friend who has that Smarty thing you have at the bottom of your response and her husband said he activated those for me. Wow, does the truck make some racket when it only runs on half the cylinders.
I always thought the grid heater worked off the temperature sensor behind the grill for the overhead display.
I really don't think my voltage swing is normal, but I just don't know what to do about it now. My batteries are less than two years old and I just replace the alternator. I'm lost.
10-08-2007, 03:03 PM
#10
Ned to find someone with a voltmeter. Check the reading right at the battery when you first start it up. You may also want to take off your terminals, clean with wire brush (or cheapo terminal cleaner tool that comes in handy), then reattach just for good measure.
I had a 2001 that jumped pretty bad while idling on cold mornings. It would dim the headlights and all. I considered it normal though, batteries were good and strong........
I had a 2001 that jumped pretty bad while idling on cold mornings. It would dim the headlights and all. I considered it normal though, batteries were good and strong........
10-08-2007, 04:12 PM
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P.J.,
I cleaned all the terminals for good measure when I replaced the alternator. I didn't check the batteries though. I'll do that tomorrow.
It is my understanding that the voltage fluctuates normally for a few minutes on cold starts, but my problem started on when it was 80 degrees. I make a trip to Medford once every couple weeks and when get off I-5 and stop at the bottom of the ramp the voltage starts to drop slowly. As soon as I accelerate it goes back to normal. I did find that if I put it in neutral and give it a little pedal the voltage comes up again.
What are the chances I got a bad "new" alternator??? No, it isn't a reman, I bit the bullet and bought a new OEM.
I cleaned all the terminals for good measure when I replaced the alternator. I didn't check the batteries though. I'll do that tomorrow.
It is my understanding that the voltage fluctuates normally for a few minutes on cold starts, but my problem started on when it was 80 degrees. I make a trip to Medford once every couple weeks and when get off I-5 and stop at the bottom of the ramp the voltage starts to drop slowly. As soon as I accelerate it goes back to normal. I did find that if I put it in neutral and give it a little pedal the voltage comes up again.
What are the chances I got a bad "new" alternator??? No, it isn't a reman, I bit the bullet and bought a new OEM.
10-08-2007, 04:38 PM
#12
Chapter President
Yes, the high idle and 3 cylinder is what you described. I've enabled it in a couple of friends trucks too. It doesn't get cold enough down here to get the 3 cylinder idle, but I've had the high idle kick in, it sure is nice on those winter mornings to have heat before I get to the office..
It wouldn't hurt to replace the IAT sensor even if it didn't fix the problem. You might even see a slight jump in mileage. The sensor is around $30.00 from Cummins, you can try a dealer, but it will probably cost more. I'm almost positive that the IAT sensor controls the grid heaters. The reason I say that is because not every Cummins truck has the overhead display.
I have around 140,000 mile on my truck and I've started to replace all the sensors. So far I've replaced the IAT, MAP, Crankshaft senor and Camshaft sensor. Some might think it's a waste of money, but I look at it as preventive maintenance. To me, since replacing the crankshaft senor the truck runs better, but that might be my imagination..
It wouldn't hurt to replace the IAT sensor even if it didn't fix the problem. You might even see a slight jump in mileage. The sensor is around $30.00 from Cummins, you can try a dealer, but it will probably cost more. I'm almost positive that the IAT sensor controls the grid heaters. The reason I say that is because not every Cummins truck has the overhead display.
I have around 140,000 mile on my truck and I've started to replace all the sensors. So far I've replaced the IAT, MAP, Crankshaft senor and Camshaft sensor. Some might think it's a waste of money, but I look at it as preventive maintenance. To me, since replacing the crankshaft senor the truck runs better, but that might be my imagination..
10-08-2007, 04:59 PM
#13
Chapter President
I found this posted by one of our admins jrs_dodge_diesel.
Notice the part about when the grid heaters turn off, truck speed exceeds 23 mph. I wonder if when you're coming to a stop and you go below 23 mph your grid heater start to come on again?
How is the condition of your belt and belt tensioner? I would think if your belt were slipping enough to cause a charging problem it would be pretty evident, just trying to brain storm here, a very weak storm or should I say a light drizzle...
Now there are two grid heaters, one stacked on the other. Each grid heater draws ~90 amps a piece. They way they operate is once the temperature drops below 59°F (as measured by the IAT, intake air temp sensor), the computer keeps the grid heaters on for an initial 10 second period prior to starting. After startup the computer uses the IAT, ECT(engine coolant temp sensor), and speed, to determine how to cycle the grid heaters. The computer will cycle them on and off the aid in engine warmup. They will cycle until the coolant temp is at least 140°F, or truck speed exceeds 23 MPH(the speed varies by year model).
Now the grid heaters draw a hefty load, 90 amps each. That is a huge load on the alternator. In effect, the lights will dim, and your voltmeter will fluctuate as its cycles. Its normal, just the nature of this beast of an engine.
At temps above 59°F the grids are not even turned on as the engine can fire up on its own without them. Below 59°F, the grids will be for 10 seconds before startup, and will cycle after sartup. At 32°F and below the grids will remain on for 30 seconds before startup and will cylce after startup. At those temps, using the block heater is a very good idea.
Now the grid heaters draw a hefty load, 90 amps each. That is a huge load on the alternator. In effect, the lights will dim, and your voltmeter will fluctuate as its cycles. Its normal, just the nature of this beast of an engine.
At temps above 59°F the grids are not even turned on as the engine can fire up on its own without them. Below 59°F, the grids will be for 10 seconds before startup, and will cycle after sartup. At 32°F and below the grids will remain on for 30 seconds before startup and will cylce after startup. At those temps, using the block heater is a very good idea.
How is the condition of your belt and belt tensioner? I would think if your belt were slipping enough to cause a charging problem it would be pretty evident, just trying to brain storm here, a very weak storm or should I say a light drizzle...
10-09-2007, 02:30 PM
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Mike,
I checked the voltage this morning and both batteries are good. One is 12.2 and the other 12.1. How would I check to see if the tensioner is in good shape? When I swapped the alternator the belt was good and tight. I have two spare drive belts in the barn. I bought one about a year ago so I had it when I needed it and then I grabbed another one when I bought the alternator because I forgot about the one I already had. The current belt looked good so I left it, no cracks or cuts.
I read a little bit in the service manual last night. What do you think about it being the voltage regulator? Do I even want to get into something like that?
I checked the voltage this morning and both batteries are good. One is 12.2 and the other 12.1. How would I check to see if the tensioner is in good shape? When I swapped the alternator the belt was good and tight. I have two spare drive belts in the barn. I bought one about a year ago so I had it when I needed it and then I grabbed another one when I bought the alternator because I forgot about the one I already had. The current belt looked good so I left it, no cracks or cuts.
I read a little bit in the service manual last night. What do you think about it being the voltage regulator? Do I even want to get into something like that?
10-09-2007, 03:40 PM
#15
Chapter President
Sounds like your belt is probably fine. I think the PCM regulates the voltage? If you knew someone with a similar truck you could swap PCMs, not sure if the year matters..