Charging System operation acting strange

[REdmon]

On my '99 Ram 2500, when I first start the truck, the charging voltage is 12V and the "Check Engine" light remains on. If I increase the engine rpm, no change in charge voltage. Approx 30 seconds later after starting, the voltage starts going up, "Check Engine" light goes off and the system shows 14V. If I turn the truck off and restart, it does the same thing. What may be going on with any of the electronic controls that I should look at? Truck and charging system work fine after the initial hiccup.

Thanks,

Ron

 

[TConver]

Grid heater on?

 

[DavidC]

Normal operation. The grid heaters will cycle in cold weather.

Dave

 

[Tractorat]

My truck (2002)was doing the same thing this last year. Replaced the alternator with oem and the problem went away. BTW, even if the grid heaters are cycling, I believe the system is designed to not turn the check engine light on just because they are recycling.

 

[DavidC]

My truck (2002)was doing the same thing this last year. Replaced the alternator with oem and the problem went away. BTW, even if the grid heaters are cycling, I believe the system is designed to not turn the check engine light on just because they are recycling.

Now that you mention it I get the check gauges light but not check engine.

Dave

 

[Tractorat]

Oops, I meant check gauges. But neither one should come on just because the grid heater is recycling.

 

[DavidC]

Check gauges comes on initially but after the 1st cycle the volt meter is the only indication of the grid heaters cycling unless the headlights or fan motor is on.

Dave

 

[Tractorat]

Im sure not a mechanic and have no business responding here. But I dont see any other responces, so here goes. I would guess that the check gauges is coming on because the voltage has dropped below what is acceptable by design. Im sure there could be other reasons the voltage is dropping so low, but I would suspect the alternator. When it happened to my truck, the shop said it was a guess, but a highly likely guess that it was the alternator and it was. Good luck my friend.

 

[Missouri Mule]

I have someone put a voltemeter on alternator output to see what voltage it is putting out when the engine comes to life.
It only take a few seconds for all the data to get to the pcm/evr so it determine what voltage the alt needs to put out. If it is cold where you are the grid heaters should cycle on and off (alternating) until you reach aproxamately 15 mph.

 

[REdmon]

The temperature is in the mid 50's. So do we think it could be a faulty alternator? With voltage going up to 14V in about 30 seconds, I don't have a clue as to what could be going on with the alternator to make it consistently operate in this manner. Only at start up at 12 V's and after 30 seconds we are good to go.

 

[Joe Mc]

My hunch is the grid heaters are coming on, as well as others have suggested. To check if this is the case or not you could start it up let it run for a bit, shut down, disconnect grid heaters and start back up to see if there's any change. MHO

 

[AH64ID]

It looks like the grid heaters are cycling normally, but the alternator may be failing and the ECM isn't happy with such a large voltage swing.

If it's the check engine light, and not the check gauges light, you should be able to scan for a code.

 

[JR]

If it only happens after the truck has been sitting for a while, check battery voltage before starting. Grid heaters should only come on very briefly at 50 degrees so I don't believe that is what is actually causing your issue. You could either have weak batteries or a slow draw and the grid heaters and starting are simply exacerbating the already low voltage.

 

[AH64ID]

The stock file shows 10 seconds of grid heater operation with an IAT of 50°.

 

[JR]

The stock file shows 10 seconds of grid heater operation with an IAT of 50°.

I'm assuming that's 10 seconds of post start operation?.
My point is at that temp no way should the grids alone be responsible for drawing the voltage down low enough to trigger a check gauges light. In 10 years of gen 2 ownership the only time I saw that light when faulty batts weren't to blame was on a cold start at around -20* F. At that point I had maximum grid operation time coupled with thick oil and reduced battery capacity. Once it fired the light remained on for approximately a minute before going out.

 

[AH64ID]

I'm assuming that's 10 seconds of post start operation?.
My point is at that temp no way should the grids alone be responsible for drawing the voltage down low enough to trigger a check gauges light. In 10 years of gen 2 ownership the only time I saw that light when faulty batts weren't to blame was on a cold start at around -20* F. At that point I had maximum grid operation time coupled with thick oil and reduced battery capacity. Once it fired the light remained on for approximately a minute before going out.

That’s from the pre-heat table. We don’t have access to the post heat table in UDC Pro, but I keep asking!


I agree that it shouldn’t throw a CEL or check gauges light, but it might be helping show a failing alternator.


The brushes on my alternator wore out and my voltage dropped to 11.8ish and I didn’t get that light, luckily I saw the gauge and turned around. It was 10° out!

 

[JR]

I would have never guessed they were on that long at 50 degrees. That must be including operation beyond the light and into start up, at that warm of temp my light would come on and go back off within a few seconds.

To the OP, I'd definitely be checking resting voltage of your batteries, after they've sat for a while but before you start for the first time for the day. Then check again after it's been running a few minutes. Most any parts house can load test your batteries and alternator.

 

[DavidC]

I bought one of these a few years ago, it is an invaluable tool for checking batteries and situations like this.

https://www.harborfreight.com/500-amp-carbon-pile-load-tester-91129.html

Dave

 

[bry1216]

Even if you plug in the truck overnight, the Grid Heater will respond to the current incoming Air Temp for at least 30 seconds. Welcome to cold winter air. Happens on my truck when air temp is below 30'f. "Check gauges" light stays on because the charge voltage is low - this is normal when voltage is low - Grid Heater take a lot of voltage - so let it idle and with less air flow voltage will recover faster, but if automatic put it in neutral for good transmission circulation.


About that Alternator, verify you have no measurable AC voltage ( .030 AC and below) between positive and negative post on battery.

 

[JR]

Dodge programmed the check gauge light to come on at 9 volts so as not to trip that light Everytime the grid heaters are functioning. It is not normal to see that light if all systems are functioning correctly, and they are not if the check gauge light is coming on at 50 degrees.