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Here's my tale of woe. '99 3500 5.9 Cummins A/T--Started out with the the torque converter lock/unlock issue, found the cure purely by accident (pulled the alternator charge line which was lying directly on the alternator away from the alternator, and problem went away for a couple weeks until the line returned to its original position--ah ha!!!). Traced the charge line, and ended up basically doing the W-T Ground Mod, things ran perfectly for about 4 years. I could not believe that crazy ground splice on the port side of the motor--engineer must have been hitting the sauce on that one. Wish I'd found this site back then!!! Forgot to mention, I bought the truck used in 2015 with only 46,000 original miles on it--when I had the tranny rebuilt at 90,000, the tranny guy told me there were some non-OEM parts in the tranny--in other words, someone had been in there trying to fix the torque converter issue thinking it was a transmission problem. This has been a source of great amusement to me, as the original owner sold this great truck because it had an "unfixable" transmission problem (and of course didn't tell me)--so thanks, MM1973, for letting people know about this easy fix even though I had to find it by accident! While on a trip out of Alaska, got a no-charge condition and ended up doing an external regulator fix to get home. Never liked the external regulator, as frequently the voltage would run high (15+). After reading MM1973's article on the fuse, decided to implement it and restore wiring to original condition (with the addition of the 5A fuse)--purchased a used PCM, sent it off to be programmed to my VIN, installed it when it returned. Lo and behold, the voltage was in the low 14s and the vehicle ran great with the exception of Brake and ABS lights (turned out the VIN programming did not take; the ABS module did not like an incorrect VIN!) and an occasional "surge" in RPM. Meanwhile, I sent the original PCM in for repair. A friend rode with me and monitored system voltage on his scanner--there was a very slight "spike" of 0.1V every time the "surge" occurred (could only see it on the graph). Strangely enough, the PCM rebuilder reported there were no problems with the original PCM (I asked them to replace that circuit regardless, which they did, and then tested for heat and vibration). When I received it back and installed it, all was well with the exception of the tranny surge--it seemed to be bad one day, and disappear the next. It was not throwing any codes, at least that my Edge reported. About 2 weeks later, while driving to work (temp was about minus 30), the surge got pretty nasty so I locked out the overdrive to smooth things out. Just before I pulled into work, I pushed the overdrive switch--it didn't shift, and my voltage dropped to 11.9. As I suspected, the 5A fuse had blown. I replaced it with a 7.5A, but still had no charging. I'm guessing the original PCM has acted up again. So I put my backup PCM in and went for a test drive. Voltage was good, and she shifted into overdrive. Problem solved, or so I thought. I turned around to head back to the shop, and got on it a little to ensure things were working properly. Instantly the voltage dropped to 11, and no overdrive. Edge pulled down a P1765, P1682 and P0753. Put the ohmmeter to the dark blue line coming off pin C3 25 to the alternator, have good continuity and no continuity to ground (same with green wire from C2 10). Going to have transmission solenoids and wiring harness replaced this weekend based on transmission guy's previous experience with similar issues. Based on the wiring diagram, it seems it has to be a transmission circuit issue. But I'm still totally baffled as to the origin of the no charge situation--either the PCM rebuilder doesn't know what he's talking about or I've got some real gremlins running around in my truck (he said it tested good, and it worked well for a couple of weeks, but now this--and after I put in the protective fuse). And full disclosure--I'm totally dumb when it comes to understanding automatic transmissions and 12V systems, but I did sleep in a Holiday Inn Express once. Sorry to be so long winded! I'd like to hear other members' ideas on this. I'll report back after the solenoid/harness replacement this weekend. Thanks in advance!

This is a writeup I did on another forum last year. I've pretty much abandoned other diesel forums so I thought I would post it here. A few weeks ago my truck suddenly decided to stop shifting and got stuck in 3rd gear (limp mode). It wouldn't up-shift or down-shift. I was able to manually down shift to second but it wont shift automatically and it couldn't be manually shifted to first. I checked for codes and got a P0753 which according to the manual is: Trans 3-4 Shift Sol/Trans Relay Circuits - An open or shorted condition detected in the overdrive solenoid control circuit or Trans Relay Circuit. I started threads on two forums asking for help troubleshooting the problem. I got several responses including replacing the overdrive solenoid, the governor pressure solenoid, pressure sensor, PCM.... I really hate throwing parts at a problem so I decided to do some research and start troubleshooting. I'm definitely not an expert at automatic transmissions but I have been repairing electrical problems for 20+ years. Using the 2001 service manual and information I found through Google searches I was able to fix the problem myself. What the P0753 is basically telling you is the electrical circuit responsible for shifting the transmission into overdrive isn't working. The circuit is actually very simple. Battery power goes through a 20 amp fuse to a relay than to the overdrive solenoid in the transmission and than to the PCM. The PCM controls the overdrive solenoid by turning on and off the ground allowing current to flow. You, of course, want to check the fuse first. Than swap the transmission relay and the horn relay (they are identical) and hit your horn. If it honks, than the relay is good. The next step is to check the circuit after the relay. You just pull out the relay and insert one probe of your multimeter into the slot shown in the picture. This is the slot that sends power to the transmission. Next, you want to remove the center (white) connect on the PCM. The PCM is located on the firewall behind your air cleaner. Just push down on the tabs that are located on top of and under the connector and pull the connector out. Turn the connector over to see the pins (holes). They are marked with small number. Touch the probe to pin 21 but be careful not to jam the probe in and damage the pin. Set your multimeter to Ohms and get a reading. It should read about 31 ohms. It shouldn't read open like mine does. This tells me my overdrive solenoid circuit is open some where. It's more than likely the solenoid itself but could be the wires or the connector on the transmission. My next step is to remove the transmission pan and filter. The overdrive solenoid is located under the filter. The filter is held on with two T-25 screws. The govenor solenoid body needs to be removed first. Its held on with four 11mm bolts and two T-25 bolts. The overdrive solenoid is actually part the of the transmission control solenoid assembly which also contains the torque converter clutch solenoid. The transmission control solenoid is held on with three T-25 bolts. Also, disconnect the wire that goes to the connector. There are also two zip-ties that need to be cut off. I wanted to see exactly what was wrong with the overdrive solenoid so I removed the black plastic cover that's over the solenoid coil and the problem was obvious. The coil wire was broken. I got a new transmission control solenoid from a local parts store for $111.00. I'd hate to see what a Dodge dealer would want for it. The new one also comes with the wires. I tested the new part just to be sure. I'd hate to get it back together and find I have a bad part. The overdrive solenoid and the torque converter clutch solenoid are identical and both tested good at 31.4 ohms. I put everything back together. I used the old wiring harness because replacing it requires removing the valve body. I couldn't see doing the extra work to replace a harness that is good. The final steps included a new filter and 8 quarts of fluid. I took it out for a test drive and it works perfectly. Total cost was $153.87. Just a few additional notes on this problem: When the PCM detects a short or open circuit in the overdrive solenoid circuit it shows a P0753 code and places the transmission into "limp home mode". What that means is the PCM shuts off the transmission relay so no power goes to the transmission. This is actually what causes the transmission to stick in one gear. This caused me some headaches while troubleshooting this problem. If you look at the wiring diagram below, you'll see the transmission relay secondary circuit receives power from the PCM (through the same wire that provides power to the alternator field winding) and than the relay power returns to the PCM for a ground. When the PCM detects a P0753 it shuts off the ground for the secondary circuit. This stops the transmission relay from closing and the transmission goes into "limp home mode'. The other thing that caused me some confusion is the 2001 service manual shows pin 86 on the transmission relay as receiving power from the PCM and pin 85 being the ground back to the PCM. This is backwards from my 2000. I don't know if it's a mistake in the manual or if they switched it for 2001. Good luck with your repair. I hope this helps if you ever have a P0753. __________________