Hi all!

New member here
I've searched the forum for any mention of P1731, to no avail.
A bit of history first, then on to my question (sorry for long post).

I've owned my 2006 Pathfinder SE 4WD for a little over 3yrs now. It was in meticulous condition for a 10-11year old SUV, as well as for the mileage.

I got it used w/ about 146k, and shortly after, changed the spark plugs, oil change, and did rear diff (just forgot to do front diff and transfer case). At the time, looked under dip stick and tranny fluid looked nice and bright (red), so I didn't even bother to change it. It currently has about 184k.

About 6 months ago, and after lots of research, I decided to replace the radiator- still had original undamaged unaffected OEM with no signs of fluid contamination (I guess I was one of the lucky ones). Along with that, we changed the serpentine belt since it was showing signs of cracking; and dropped tranny pan, replacing filter, about 4qts of fluid, as well as changing rear diff, front diff and transfer case fluids/oils. End of history

Now the problem

For about a year maybe year and change now, I've been experiencing intermittent RPM flare/flutter and transmission "shudder" (which feels like I'm driving over heavy uneven terrain for a split second) for the past year or so and it started very intermittent, but has progressively gotten worse (more frequent).
The shudder almost always happens when doing either a quick stop-and-go (rolling stop), usually as it shifts into 2nd gear.

The RPM flare happens less frequently on lower (and sometimes higher) gears, i.e., upshifting 3rd-4th, 4th-5th or downshifting from higher to lower gear, when I step on the gas to accelerate and overtake someone on the road or highway.


I have the following DTCs currently showing up when I scan my car:

The dreaded Catalyst below efficiency threshold on one of the banks (I forget which, as it's been there for a while, and I simply chose to ignore it).

Something about my TPMS not communicating (light is constantly on, and sometimes flashes).

And finally (and worst one is the P1731 outlined below):

This P1731 Nissan DTC refers to A/T 1st Engine Braking / 1-2 Shift Malfunction

According to a quick google search:
The P1731 Nissan OBDII code references a fail-safe function that prevents an unexpected decrease in speed from engine braking when the gearshift is not in the 1M position.

Symptoms of a P1731 include Harsh shifts and causes are listed as:

• -Damaged wiring or connectors
  -Solenoid wiring problem
  -Failed low coast brake solenoid valve
  -Failed ATF pressure switch 2

To properly diagnose a P1731 Nissan OBD2 code, the wiring and connectors between the solenoids and the ECU will need to be checked for signs of damage and corrosion. After that, the low coast brake solenoid valve and ATF pressure switch should be checked.



Has anyone else had only this code pop up, and would a new valve body (and TCM) fix this issue?

Thanks in advance!!

I took to my father-in-law's mechanic and he referred me to his tranny guy, who is a more of a small operation/shop, and not a full blown transmission shop (if that makes sense).

He first said it might be the Torque Converter (because of the shudder), and also said it was most likely the TCM and urged me to get a whole new (dealer) valve body assembly, at a cost of (1100-1300, after install by him, and dealer flash ).

I'm concerned that there are no other codes, nor symptoms that relate to a faulty or soon-to-be-dead TCM (and inherent circuitry, solenoids, etc.), but I HAVE heard of these transmissions being EXTREMELY finicky. I'm also afraid that, even after I get a new valve body/TCM assembly, the TC will go out next, requiring a new one or worse a tranny rebuild.

I found a trans shop online (out of Tampa, FL) who sold me a reman valve assembly already "flashed to your (my) VIN", for $540 (shipped to me), with a 3 year warranty (1yr free replacement, 2 year troubleshooting).

What are your thoughts/suggestions?

Several questions. First, can you do the electrical checks in the service manual yourself? That would at least eliminate some of the easier root causes in the FSM, particularly if you have a grounding issue. Next, maybe take it to a Nissan dealer and spend the $100 to get them to diagnose it with CONSULT II. I'll check, but don't think Nissan DataScan will do this one.

If it's not electrical, yeah maybe the valve assembly.

Don't know about these transmissions being finicky. There are brands where you expect to have issues like BMW. Not many forum posters have had transmission issues outside of the coolant leak problem with the radiator. Mine is at 180K miles and still among the "smartest" automatics I've ever driven.

One of the things that sometimes happens on these valve bodies is the metal "pin tracks" that create the circuits between the TCM and valve body develop cracks and, ultimately, the track will break and cause an open circuit. In such cases, the valve body can be removed and the broken or damaged pin track can be repaired (soldered). Of course, as mentioned per the code description, there are other things that can trigger this code, as well. Going through the diagnostic steps for that code and inspection are the only way to be sure of what the problem is. Check out this YouTube vid:

https://www.youtube.com/watch?v=7wCRqD9o5bc

Thank you all for taking the time to respond.

ShipFixer wrote:Several questions. First, can you do the electrical checks in the service manual yourself? That would at least eliminate some of the easier root causes in the FSM, particularly if you have a grounding issue. Next, maybe take it to a Nissan dealer and spend the $100 to get them to diagnose it with CONSULT II. I'll check, but don't think Nissan DataScan will do this one.

I don't have the full service manual, just a A/T section of pdf I found online which goes over diag procedure for most AT related codes.
As far as knowledge about what to look for in the circuitry, I'm afraid I'm not as familiar with transmission wiring/harnesses in general, so I would not know what to look for.

I DO have an update however. In my searching for shops/mechanics, one checked the dipstick level and found it was not reading, almost as if completely dry. That was odd because when we dropped the pan and did fluid last time we made sure it was at proper level (unless perhaps we missed it). So he went on to add a full quart of oil. This was 3 days ago. Then yesterday, I thought I would check the fluid again, and lo and behold, level was low again, very odd. So I added some more and went incrementally slow in doing so. It seems right after adding, it will give a reading as if full i.e., at proper level. However, removing the dipstick several times, wiping it and reseating then waiting a few minutes and repeating this, I was finally able to dial it in to proper full hot level (engine running in park at level surface, the entire time). So all in all I added about 2 whole qts in the last 3 days.
Then as I drove to my next shop, I noticed that the flutter, flare and shudder disappeared!! Now I imagine it's probably too early to tell, as this was only yesterday. But I also scanned it again, using a much better scanner (found a whole bunch of more codes, abs, tpms and steering related, as well as the cat efficiency) but still only the one TCM/tranny related one showed (P1731). So I proceeded to erase the ones that were generic or non related to my issue and at some point the TCM code went away on its own (again, a bit odd). I eventually erased them all and my check engine light went off.
Haven't driven it since (and honestly I'm expecting for some of the codes to come back), but we'll see what happens.

Could my issues have been related to low tranny fluid...or is it too early to tell?

Thank you all for your feedback, btw!

smj999smj wrote:One of the things that sometimes happens on these valve bodies is the metal "pin tracks" that create the circuits between the TCM and valve body develop cracks and, ultimately, the track will break and cause an open circuit. In such cases, the valve body can be removed and the broken or damaged pin track can be repaired (soldered). Of course, as mentioned per the code description, there are other things that can trigger this code, as well. Going through the diagnostic steps for that code and inspection are the only way to be sure of what the problem is. Check out this YouTube vid:

https://www.youtube.com/watch?v=7wCRqD9o5bc

Thank you. Yes, I've watched several of these videos, which is why I was hopeful that perhaps my issue is something similar (and I can fix it myself, once I get over the fear of removing the valve body assembly myself).

As I mention above, I'm praying that somehow, my issue was low fluid related, but I suppose time will tell.

Oddly enough (or not), all the mechanics and shops I mention this to just shake their head and tell me this will not fix anything (taking TCM out of valve body and further, more closely inspecting it), which clearly it has been successfully done by several folks on YouTube.
I don't know what to make of it.. they're either trying to steer me clear of doing this so that I can just fork over 2500 for full rebuild, or they're truly onto something. In any case, they all shrugged when I mentioned wanting to buy a remanufactured valve body online (which I did, it's currently on its way to me), and all said they purchase a new one from dealership in all their rebuilds.
But my thought is, if it's already broken, what's wrong with trying to inspect it further and truly get to the bottom of the issue. Is it bad solenoid(s), broken circuitry (metal pin tracks), or something else altogether..?
I'm by no means a mechanic, but this is exactly why I like to dive in and learn about repairs my cars need and always try to do it myself... its just so hard to trust others, especially when you hear so many horror stories of people being taken advantage of.

What are y'all's thoughts?

Full service manual here:

viewtopic.php?t=2

Transmission (TM) section here:

filelib/R51B/TM.pdf

Depending on how your reader works for the front section (FWD.pdf), you may have to put the two letter code in to download it. I.e., replace "FWD" with the two letter code of the section you are after, EC, EM, etc.

Awesome, thank you SF!!

If the problem is caused by a broken pin track, well then it can be repaired. However, broken pins tracks nor bad valve bodies will cause transmission fluid loss. The pin issue only represents one of the possible things that can cause the code, but as I eluded to, that requires diagnosing the problem, first.