Need some Help.. Low voltage/Transmission Issues
 

SO short story long...

Truck:
1997 Dodge Ram 1500, 4x4 Sport 360/ 5.9L magnum

My truck is reading low-voltage on the dash (about 12). It started about 3 weeks ago, I took the alternator in to have it bench tested- it turned out the DC current wasn't reading correctly. I ended up getting a new alternator under warranty- and installed it. The problem persisted. The battery is less than a year old- I tested it both with the truck running (12.5-13 volts) and without it running (12.5-12 volts). Nothing unusual there except the low voltage while running. New serpentine belt. Replaced every wire/cable to the battery and alternator- including terminals (plus cleaned). New (Refurbished) computer- that I've twice now called upon for its warranty- so I don't think its the voltage regulator in the PCM. I'm completely stumped as to what it could be... Replaced several fuses.

I've got two OBD1 codes:

31 (canister purge solenoid, I know this isn't the issue- I purposely removed this sensor as it served no purpose except to pass emissions)
37** (torque converter clutch open or shorted or transmission temperature sensor above or below acceptable values)

Considerations
Obviously the code that jumps out at me is the one related to the transmission- could a bad sensor or short cause my voltage to be low? So low that it causes my voltage to remain at 12 while running, eventually causing my gen light to come on and the truck to go into "limp-in" mode? Is it likely I got a second bad-alternator in my warranty? Its important to note the transmission has no other issues- it shifts good and strong, but this is the only thing left that comes to mind. The truck runs and shifts great besides the low volts- which, like I mentioned, eventually causes the gen light to come on and truck to go into "limp-in" mode if I run it too long.

I'm not very savvy when it comes to transmissions, and even less about electrics/sensors in cars- before I crack open the transmission and start replacing fluid and sensors- can anyone think of something I may have missed? Or any insight would be helpful and welcomed. Thanks guys

PS: dumb question- Will I need to crack open the transmission in order to replace the torque converter clutch and or the other sensors? Thinking I will need to replace the TCC regardless, remembered it slipping a bit at 30-45 mph last time I drove it- a month ago or so- but never done one before.. Thanks

I assume you are testing voltage with volt meter not by what the gauge is reading? Did you check both at the battery and the alternator terminal? Any difference in voltage? You put on a new belt but is the tentioner keeping it tight?

Yes drop the pan and the valve body. If you are going that far replace the pressure sensor and solenoid also

Cool man, thanks.
Yes you are correct- tested in with a volt meter.
I didn't test the voltage at the alternator terminal- would that help determine a bad alternator? Also, the tension pulley was replaced with the belt (a couple months ago).
Yeah I just tested the computer (again) with my friends "nicer" scanner tool...

Getting the following codes from it:

P0743 -TCC, electrical problem
P0748 - pressure control solenoid, electrical problem
P0753 - Shift solenoid A, electrical problem

From what I understand all three of these codes share power from the relay-

Okay, so in light of the new codes I'm getting:

1) Are these solenoids ( I guess I mean the Shift solenoid A) all located in the transmission?
2) Could these also be responsible for my low volts on the dash, and whats essentially draining power?

Update:

Checked my transmission fluid (neutral, mid-temp) and it was practically empty. Or so it seems- I did notice a smell a month ago or so, but ignored it. I guess there may be a slow leak? Oops, thankfully don't drive it much. Could this be causing the sensor issues, as well as the electrical issue? Does low transmission fluid cause the sensors to fail, and make the pcm voltage regulator act up?

It's more likely the low voltage is causing the other codes.

I would suspect that your voltage regulator in the PCM took a dump, and the rest of your issues follow from that. So, you know the alternator tests good, verify what voltage it is putting out AT the alternator. If all you see there is battery voltage, then you get a choice: Replace the PCM, or, install an external voltage regulator.

That was my initial thought process- but I literally just installed a new (refurbed) PCM into the truck on Saturday, after having sent another one I purchased back to the seller. What are the odds of two refurbished PCMs voltage regulators failing back to back like that, pushing out seemingly the same codes? I actually have an external voltage regulator installed in the truck, the wires are just disconnected. I just didn't like having to remember to turn the killswitch on/off (I forgot to on several occasions and it drained the battery), I ended up biting the bullet and buying the refurbed PCM for a good deal.

I will test the alternator tomorrow in better light, but that's also a brand new warrantied alt. that I installed a couple weeks ago to try and fix this very issue- the guy at the autoparts store mentioned the original one had no DC voltage going to it, and handed me the new one no questions asked. Now, whats the likelihood of this new alternator being bad? Suppose I'll check it out tomorrow. Thanks for the feedback guys

Depending on where you got the PCM from...... the odds of getting one with the exact same problems..... really aren't that bad. :)

That would be quite some current to see so much voltage drop but one test would be to disconnect the transmission wiring harness and start the engine to check the voltages. Don't try to drive unless you're familiar with the manual shifting procedures.

Is there a battery temp sensor, under the battery? That might give you a low voltage, though I think it should throw a code, if it's not working.

First off, thanks for all the responses! Maybe crack the transmission open next week and investigate that. Also HeikIlm, no- no battery temperature sensor as far as I know, I've removed the tray once before, but don't recall seeing one under the hood or even in the repair manual.

Small update:

So after testing the alternator, everything checked out- no weird grounds or draws. I removed the alternator and had it tested; everything normal. I ended up hooking the external voltage regulator back up, and now the voltage is running at 14.45-14.65 volts- kinda strong, but its a better than the previous situation. Went and drove it and immediately noticed really bad acceleration- took it back home and hooked it up to the scanner. Now I'm getting a P0205 code, in addition to the other transmission codes (no surprise there). So now I've got some issue with injector circuit at cylinder #5. I guess this explains the bad acceleration. Gonna check it out today, hopefully its just a bad connection. Saving the transmission repairs for better weather (its still kind of winter here in Montana).

Just when you think your done fixing your truck, another issue pops ups- looks like I got my work cutout for me:icon_smash::icon_lol: