Dakota Durango Forum banner

P1698 PCM/TCM buss comm failure

2633 Views 8 Replies 2 Participants Last post by  DoubleJ
I tried over in the transmission forum, no luck on three different threads, hopefully you all can help. Recap below:

Here's the story: Truck has always had an occasional issue where the TCM loses power, the trans drops a gear down, then about 5 seconds later upshifts, and I'm on my way. Sometimes 5 times a day, sometimes 5 times a year.

Last week, started the truck and had a CEL, also had all gear positions lit on the dash. Weird. Truck drove fine, gear position thing fixed itself, CEL cleared after three key cycles, so I shrugged it off.

50 miles later, truck shifts itself D-N-D-N-D while I'm sitting with my foot on the brake and over the next 50 miles it won't stay in the selected gear, it won't fully engage 1st, it just doesn't work. P1698 has come and gone, truck won't move forward (reverse seems to work fine, maybe it's only mechanically controlled?), all gear positions are illuminated and when I try for a forward gear, I don't get the normal relay buzz that I'm used to as it pressurizes the clutch pack.

I figure that with no talking to the PCM and no talking to the transmission, the TCM is just out. 10 bucks for a replacement, no change at all. I've located every ground I'm aware of, all good. I swapped relay 31 as it was freaking out, no change. I checked "trans power" fuse, good. I checked wiring under the dash for anything obvious, no luck. I checked the big fat wire from the TCM to the PCM to the firewall, looks good. Pulled, and broke, all three PCM plugs. Everything seems in order. Pulled my line pressure modifying doodad, no change.

Engine runs like a top. Dash is normal other than what's coming from the trans. Battery is new.

Ideas? PS - 2000 4.7 2WD Ext Cab. Blue.
1 - 6 of 9 Posts
Ordered up a factory service manual, and P1698 isn't even listed in transmission codes, so it must be listed in another of the 5 manuals in the series. Anyone know what book it's in?
That would be in the main service manual, like below? The expensive one.... I got the trans diagnostic procedures manual for 14 bucks.

Orange Amber Publication Font Gas
See less See more
Ok, I'll have to locate one, I tried to save money by buying just the trans manual, wasted 14 bucks in this instance, I think it's only got TCM codes in it.
Spent last night searching that PDF, there are the two mentions of P1698 that you highlighted originally, but nothing else nor a troubleshooting procedure. There is an electrical schemo and pinout for the TCM though, so that gives me a starting point looking for battery and bus voltages.
Follow up, plates expired in March...got a renewal notice last week for some reason (got 2 renewal notices for my Hyundai even though I'd already freshened the plates...DOR is slipping) so I figured I'd better get this fixed since I need an emissions test to get plates. Went to the Dodge dealership prepared to pay out the wazoo just to get it fixed, and they noped me. They don't work on Dodges (this is the Dodge dealership I'm talking about) older than 2008. They did, however, print me the schemo I needed after I explained what was going on. 2 hours with my multimeter and I found that the pin that is supposed to be carrying 12VDC directly from the fuse box under the hood is carrying 1.7VDC. A temp wire and two scotchloks and I'm in business, truck drives all over the place with 4 gears like there wasn't ever anything wrong. Today I put about another 2 hours into it running a new permanent power wire from the fusebox to a splice in the TCM harness and I'm in business. Topped off fluids and R134 and went to Taco Bell. Gonna run a fresh tank of gas through it, wait for evap readiness, balance tires and then head to Air Care Colorado to pay them 25 bucks to say they won't put it on their dyno and pass me.
See less See more
1 - 6 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.