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Hi all, Started noticing a problem with my truck when it shifts into overdrive. Driving down the road, truck shifts through the gears normal kicks into overdrive and then starts acting differently. It will cruise fine under light throttle... as soon as I give it throttle, it responds very sluggishly, starts throwing consistent black smoke, the EGT's will jump up, and the truck is vibrating. It will continue to do this until it really gets up and going, or if I let off the throttle. It really is a pain because the truck drives in overdrive a lot on the 35-50mph roads around here. This has just started happening and seems to be getting slightly worse. Any ideas/help as to a diagnosis or where to start looking? As always thank you in advance for any help. - FYI...recently put a new turbo in the truck which is considered a slight upgrade I believe with the 59mm inducer. - Edge Juice with attitude, fass150, 4'' turbo back exhaust, BHAF

Hey! ok so ple ase help me here I just bought a 98.5 cummins about a month ago and it has this issue that I just cant seem to tackle and its super frustrating! if I have ac on just cruzing along in overdrive (48+ mph) it jumps in and out of overdrive! but as soon as I turn the ac off.. no problem! it runs great.... turn it back on it goes right back into this cycle of going in and out of overdrive. when I first got it the ac worked but the fan didn't work so when I took it home and got to lookn at it closer I noticed a wire going to the + battery turminal and it had a blown fuse right there too.. replaced the fuse and fan works great now...... just tonight I put a APPS noise insulator on hoping that would fix it but it didn't... anybody got the same issue, or know a fix? thatd be super helpful!

I have a 92' power wagon 250 with the 5.9L 12V intercooled, A/C, power windows, locks, and lots of electrical problems! My biggest problem right now however is that my over drive will disengage at speeds of 75MPH or not engage at all. I noticed that the problem happens when it's moist or wet out although it still occurs when everything is bone dry, also the tachometer will not read true or not give a reading at all while the problem is happening. But if i step on the brakes the tachometer will work but it still wont shift. my battery voltage drops a considerable amount as well sometimes down to 10V, all these problems come and go at the same time. please help!! I bought a book for the truck but it's useless. (no diesel info at all)

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. __________________