2nd Gen Non-Engine/Transmission Battery Voltage Gauge Drops to Low End of Scale Yet Alternator is Still Charging!

[DieselDave]

Hi Guys, I need to tap your technical expertise about this problem.



On the first of two occurrences (about two months ago) I was 1-1/2 hours into a 3- hour long trip and towing my camper when I noticed my “Check Gauges” light on the dashboard illuminate. I noticed that my battery voltage had dropped down to the low end of the scale and stayed there regardless of my engine RPM. Within a few miles I pulled over, left the engine running and visually inspected everything under the hood – I saw no issues or smoke, etc. . The batteries did not seem to be hot at all. I had no voltmeter with me to further troubleshoot the situation and it was late on a Sunday so I completed my trip to my home. Upon arrival, I promptly measured the voltage at both battery terminals to find ~13. 9 VDC. I then disconnected my camper from the truck (no difference at voltage gauge) and shut down the engine. It started right back up without issue and the battery voltage gauge went back to normal ~14 VDC. I load tested both batteries and they checked good. I checked for DTC’s – there were none. I cleaned the battery terminals and cable connectors which were in need of cleaning.



For two months I used the truck off and on and towed my camper again on two different camping trips without a reoccurrence of the problem. However, yesterday I was returning from another trip, again towing my camper when the same problem occurred. This time, and just a few miles after the gauge dropped, I stopped at a stop sign to shut off and restart the engine to see what effect that might have. Upon the restart, the gauge came up a little but then dropped all the way down again triggering the “Check Gauges” light once more. Once home, the voltage at the battery terminals was once again at 13. 9 VDC as measured with a voltmeter.



The batteries check good. The Denso alternator is the original with the vehicle (233K+ miles) but still seems to be charging the batteries although the battery voltage gauge on the dash is indicating something different. Do you have any suggestions for me as to what might be causing this problem? Is there something else that I should be checking? I use the truck to tow during the cold Winter months as well and so if I have a failing part I really want to address the issue now during the nice weather so I don’t have an issue over the road or in nasty weather.



Thanks in advance guys for your technical guidance and support.

 

[SSolderitch]

Voltage regulator is in the pcm. You can make it external with a mopar unit and splice it in the wiring. Searce the TDR. However I was told a external vr may affect an auto trans?

 

[B.G. Smith]

Since you seem to be maintaining 13. 9 volts at the battery I would suspect a bad ground somewhere, maybe from cab to engine, cab to dash etc. bg

 

[CAPTPHIL]

Dave,
Before you spend a lot of time, check your trailer plugs both the truck and camper. From what you have said it only happen with the camper hooked up. Take your camper plug apart and check each wire connection also check elec. brake wires all the way to the wheels. I have had these problems several times in towing 1. 5 million miles. If they use salt on the roads it will work on the electricals on trailers especially when you are towing in the summer in the rain as the salt from winter will be pulled out of the pavement. Also check and clean all grounds on the trailer.
Good Luck Capt Phil

 

[DieselDave]

Thanks to all - I will check the grounds and likely replace the alternator since it has got to be on borrowed time with 233K + miles on it. I will update this post again in about a month with the results.

 

[WilsonF]

Please take your alt. to a rebuild shop to have it done, don't get a rebuild from a auto parts store. The quality of yours is much higher than any parts store rebuild.

Floyd

 

[hcole]

Dave, it seems to me like its time for brushes in the alternator. Sometimes they will start operating intermittantly when they get short and start to loose tension in the springs. Had this happen a lot on GM alternators.

 

[BK]

When my alternator went, it wasn't the brushes ,it was a diode pack.

I had the same problem a couple of times I saw the battery meter go down, check gauge light and donging...

And it would last a short time and all would come back.

Finally it just died , and was constantly low.

Even though was only putting out 12. 9 vdc, the body of the alternator was much much hotter than the brackets... diode pack must have shorted.

 

[Batman]

FWIW, I would definately check grounds, and camper connections as mentioned above. I had a lot of corrosion on one of my plug connections for my camper where the 7 lug connection was added in.
HTH
g

 

[Ramtuf1]

That happened to me and I thought it was the alternator. I had only about a year on it so was still under warranty. Installed another and still had the same problem. Had it checked out at a dealership and turned out to be the small weather proof two pin connector which plugged into the bottom of the alternator. With all the cycling of the heaters etc. caused one of the wire connections to arch and burnt out the pin/socket connection inside the connector. . They replaced it and has worked fine ever since.



This caused some problems with the TC lock/unlock as well and took care of that also.

 

[DieselDoghouse]

What BK said!! Excluding gremlins in the trailer wiring…you need to go where they can definitively tell you you have all 3 phases of the alternator contributing to charge (see my prior posts about how an alternator works). This ain't gonna happen at the local auto parts store. You need someone who can 'scope (oscilloscope) the output waveform OR pull the diode pack and check the feed-thru (low) feed-back (very high) resistances of each diode. As far as alternator brushes - since they supply a single winding (the rotor) they should affect all other windings (the 3 stators) equally and you should get very obvious low output.

 

[DieselDave]

Update - After checking all of my vehicle grounds, the alternator connector and then the trailer wiring connections on both the truck and camper I found nothing wrong or unusual in any of those places. I then replaced the alternator with a new replacement alternator and have driven the truck for several hundred miles since and twice with the camper in tow. To date I have not seen a repeat of the problem. I hope that this thread helps others in the future.

 

[fest3er]

Yepper. Diode failures can be temperature-related.

I'll bet at least one diode was very close to failing. My old 200SX once behaved in a similar manner. Cold or even warm, it charged like a banshee. But driving across DFW area in stop-n-go traffic, it got really hot and one diode stopped doin' its thang. Once it cooled below the failure threshold, it started working again.

 

[BK]

Good to hear, yea, I'd lay a few bux it was a diode flaking out.

 

[rkressg]

I had a very similar failure with the voltage gauge on my truck the other day. The truck has 200k on the clock, on the original alternator.

I took the Alternator off the truck, and pulled the brushes out. They were just about worn down, and I could see that they were arc-ing. $20 for a new set of brushes, and the issue has not come back.

The Denso Alts in these trucks are virtually bullet proof, especially when compared to the AC Delco used by other Mfgs. Bearing Failures and Diode pack failures are not very common in these units until getting up into the 300k+ range.

The brushes are not hard to get to on the Alt, you will just need a screwdriver (after pulling the Alt off the truck).