Hi All.

I have a '99 5.9L Durango 4x4 with 137k miles on it. Over the last few years, I have been handling more and more of the maintenance as I find that I enjoy it, and it saves me quite a few bucks.

Yesterday, I picked up (2) OBD codes. P0753 and P1765, and the transmission defaulted to 'limp mode'. Both of the OBD codes are transmission related, and based on the research I have done on the internet, it seems I am likely to end up replacing the PCM.

Could anyone suggest where I might find a wiring diagram of the transmission electronics? In particular, I am interested in the PCM, relay, and transmission connections.

For those interested in the trouble-shooting:
1. I replaced the ($20) transmission speed sensor output, and it had no effect.
2. Verified the 20A transmission fuse has continuity.
3. I verified the transmission relay is good. I swapped it for the Horn relay which is the same relay type. I also verified the relay coil had a reasonable resistance (75ohms) which happened to be the same as the other relays.
4. I ohm'ed out the PCM middle-connector, pin30 (pink wire) to the fuse/relay box, so I do not believe it is a broken wire/bad connection.

5. Next up is to force a ground onto the pink wire, which from my understanding, should energize the relay, hence powering the stuff downstream in the transmission. Apparently, if this works, I probably have a bad PCM, so I will be looking into getting a new/used one.

 

seems to me that its a 3-4 shift solenoid, on the 5.9 the only real computer control is for OD, the rest is (for the most part) done hydraulically, limp mode is usually something which affect the engine, rev limiter at 2k(i think) and very low power output from the engine.

 

Thanks for the feedback. The truck is definitely starting in 2 or 3rd gear (slow/boggy type acceleration), performance is fine once up to 25+ mph.

After that, the RPMs start to get pretty high (~3500RPM to get 65mph).
OD button has no affect.

 

Check the harness where it plugs into the transmission for corrosion.


Also remember that limp mode is 3rd gear not 2nd.

 

I got around to step #5 this evening, and the transmission worked fine, so I think I have a bad PCM.

As an aside, several of the tips I saw on the internet suggested to scrape back the coating on the pink wire (pin 30) of the PCM connector to be able to connect it to ground. I chose another method... Pin 30 connects to pin #2 of the transmission relay. I pulled the relay, wedged a wire into its contact receptacle, and then re-installed the relay. I then ohm'ed out the connection between the wire and pin 30 at the PCM harness to verify good contact was made. I then grounded this wire.

I started the truck up (did not bother to clear the codes), put in in Drive, and drove away (in 1st gear). The transmission then shifted normally through all gears up to and including overdrive. Nice.

It looks like the next step is to buy a new/used PCM computer. What a shame. For those electronics geeks out there... I am almost certain that the PCM computer has an Open Collector or Open Drain output circuit that is used to 'connect' pin 30 to ground to activate the relay. Open collector ICs are about $0.20. A rebuilt PCM is about $250.00.

 

Posting a follow-up. I ended up replacing the PCM with a rebuilt that I bought on ebay from http://www.allcomputerrebuilders.com/.

It fixed the problem, and has been working perfectly for ~1 week so far.

 

Thanks for the update!

 

im having same issue with my 98 durango...limp mode, done all the testing put a bunch of new parts on it etc...and its down to replacing computer. i have been told that if i just buy a used one and put in it that the abs light and brake lights will stay on??? some kinda a vin number not matching issue? does this sound legit? i have seen companys on ebay also selling rebuilt computers and wondered if that would cure my issue...i just don't want to go back to dealer.....$$$$$

 

FWIW - I replaced my PCM (as described in the thread above) and did not and still have not had any issues. The vendor posted in my link above asked for my VIN number and mileage as part of the PCM flash, so I dunno, maybe they flash it with some model/VIN specific info that keeps the ABS/Brake system happy.

 

yes the pcm must be flashed to your vin # and mileage in order to work properly, yes anybody selling you a pcm should request your VIN# and mileage so that they can flash it to the computer and then ship it out to you pre-flashed so all you need to do is plug it in