Clayzer

I have a 2000 Jeep XJ with 220,000 miles. I was going over a pass and my CEL light turned on. I ignored it and ended up over heating my tranny and blowing the front seal out. After I got towed back to town, I discovered I had a P0740 code. Things Ive done to fix this issue:
Ive replaced all 3 solenoids on my original transmission: Replaced filter, Replaced fluid, Replaced blown seal, put tranny back into my jeep and it continued to puke fluid....

Got a used transmission. Drove for a few miles and got P0740 and P0743
Changed solenoids in new transmission, fluid, filter, Inspected Solenoid wiring
Checked TCM pin 24 to ground (OK), Pin 11, 12, 13 (All between 13 and 15)
Replaced TPS
Replaced Brake sensor
Jeep will shift into 4th gear and lock torque converter when transmission fluid is below 160. Once it gets above 160, it will stop shifting into 4th or locking torque converter. Fluid will get slightly over 220 and that is with an AUX after radiator transmission cooler.

Since I am having the same issue with two different transmissions, it makes me wonder if this is on the JEEP side and not the transmission.

What else should I check. Replace TCM? Ive also scoured the internet on this subject and nobody seems to actually know how to fix it.

lawsoncl

Using the correct trans fluid? Not ATF+4. You've hit all the usual causes - solenoids, check wiring, brake sensor, and TPS. I doubt it's the TCM, as I can't see how that would be trans temp dependent. You swapped the trans, so you would have looked at those connectors. Possibly the NSS is bad and telling the TCM that you're in (3) instead of (D). Bad grounds are often an issue, and never hurts to check those especially the one at the dipstick where a lot of stuff converges. You could jerry-rig in a meter or a test lamp on the solenoid wires to verify whether the TCM is powering the solenoids.

Clayzer

Im using Dec/Merk III from Autozone. I just put in new fluid the other day but this whole transmission ordeal is making it run super hot. Up over 220. I checked it last night and its pretty brown but still shows up reddish on a paper towel. It also might be brown because the "new to me" transmission might have had brown fluid in it to begin with. I hear walmart has some pretty cheap ATF. Think its worth flushing it and then putting in some good stuff? Maybe some of that Lucas tranny saver?

I forgot to mention that I cleaned the G101 ground and the one by the battery but I haven't done the one by the dip stick. All the connectors check out and have been cleaned. I get in spec ohms when testing the solenoids.

When I drove this morning, I went into 4th gear and locked up the torque converter just fine, however after 20 minutes of driving, it quite locking up and ran about 2100rpm at 60mph. Trans temp slowly ramped up. Tapping the brake didn't do anything to the RPM neither did pulling back on the brake to verify that the sensor was pushed. Does the NSS slowly miss read shiftier location?

Clayzer

Update:
I was able to get my hands on a used TCM and swapped it into my jeep. P0740 quickly popped up. I just flushed the tranny with clean Dex/Merk III and put some Lucas Oil tranny fluid in it. Level is about 1/8 under MAX on level ground in park. While going on my test drive, the TC was able to lock up and ran for a few miles. However when I had to climb a hill, it would not lock up again and then kicked out the P0740 code again.
Remember all my solenoids have been changed, wiring from TCM is between 13 and 15 ohms on pins 11, 12, 13. TCU pin 24 has continuity. TPS has been replaced. Grounds have been clean.

How can the TC lock up and then just stop when the fluid gets a little warmer?

Clayt

https://www.carparts.com/blog/p0740-...t-malfunction/
Check this link out maybe it will help.

awg

So I have had an issue of the TC not locking up intermitently, and now the situation is permanent, trans got swapped when it failed due to an unrelated overheat, swapped solenoids etc etc

NOW, when I measure the resistance it is open circuit, and I am 99.9% sure its in the wiring that goes from the solenoid itself to somewhere just outside the box itself (checked 2 x solenoids and they measured ok and worked when on the bench

those wire are very skinny, and I suspect its right near the rubber bung that comes out the top of the trans ...oh joy

do a resistance test when from the plug near the dipstick to battery negative when its HOT and wont work...for instance I got a reading of about 30 ohms for a while before it stopped working

I do so hate XJ wiring..good luck bro...its all I can think to try...let me know how you go...still got to fix mine

Clayzer

AWG,

When I had my blown up transmission on the floor, I noticed that the protective casing that goes around the black harness wiring that goes to the solenoids was worn through in two spots. Where it crosses over the tranny on the top and where it turns by the shift lever to go back to the solenoid bung. Check those spots out for damage.

The wiring on my replacement tranny was good.

awg

thx for the reply, but I pinned thru the wire very close to to the trans, about 3" before it enters the case, so I know it has to be in that short distance between there and the solenoid itself

lawsoncl

Yup, it sounds like time to drop the pan and have replacement solenoids on hand. It could be the wire, but I think more likely the solenoid itself has gone open. It's also remotely possible the connector has fallen off. I've seen where you needed to crimp the spade connectors a hair with the replacement solenoids to get them to stay on.

Sig220

Ahhh, the intermittent PO740. I have that!

To the OP, you might want to check to see that there is not a blockage going to from the transmission cooler. That could cause problems with both transmissions.


On occasion, the CEL will come on and it will always be the PO740 code. Sometimes it is accompanied by the torque converter not locking up, sometimes not. I can tell that when its not locking up as I run higher RPMs then normal. I have decent looking tranny fluid, after draining the pan and refilling a bunch of times. I have not checked the tranny temp, however. Most times, the CEL will quit coming on after I reset it, sometimes it takes a couple of days of resets but it has always cleared up eventually. I have checked/cleaned the grounds by the dipstick (with the others) so I am confident they are good. I suspect the wiring
grounding out to/from the solenoids or the connector at the firewall near the back of the engine. Sometimes, I can get the CEL to stay off by cleaning the contacts on the connector!

So there is my experience with the CEL and the PO740 code. Maybe it will help another. So you don't have to look, my XJ is a 99/auto/4WD 4door.

This experience has not been bad enough for me to drop the tranny pan and check the wiring there or even run a continuity check between the connector and the solenoids. It is not mechanical (maybe a solenoid going out) at worse but I suspect electrical,in my case. I have seen it set off by driving through water before so there is that.

If this was my only vehicle, I would be more determined to get it solved but its not

Sig220

Must have been "Karma" took the XJ and pulled a 12" trailer with about 500 pounds of construction stuff to a creek cabin I have been rebuilding. The drive up (about 60 miles) was uneventfull held about 2000rpm and was running about 60-65 mph.

Then when we started back, I noticed that holding the same speed was running about 2200-2250rpm. Even made a comment to the wife that I may have jinxed the XJ with my post this morning. I pulled it back to an even 60mph and was running 2100-2150 rpm.

Sure enough when I got into the last 10 miles of the return trip the CEL came on and it was the PO740. The funny thing about my experience with PO740 is that you can reset it just before you cut it off and it will set the code as soon as you turn the key to accessory.

So after I got everything unloaded, I cleared the code an shut it off, turned the key to "on" without starting and cleared the code again. I will let it sit overnight and check its status tomorrow! What a PIA it can be sometimes!

Clayzer

SOLVED... Hopefully

Well, I think I have this P0740 issue licked.
To recap things I did:
-Check engine light kicked on and I ignored it. Over heated transmission and blew front seal puking ATF all over the highway..
-Dropped transmission, replaced seal and bushing, reinstalled tranny and it leaked.
-Purchased used tranny and installed it. Still had the P0740 code,
-Replaced solenoids
-Replaced TPS
-Replaced TCM
-Visually inspected wires and tested for continuity to the solenoids
-Cleaned ground locations
-Replaced Brake switch
-Flushed fluid
---None of this stuff worked---
-Purchased new Torque converter

-Decided to clean NSS, broke the big bolt.... Cussed... Took NSS off OG tranny and cleaned it, sanded contacts, added dielectric grease, and put back into Jeep.

==Problem Solved== .... So far.... Jeep will get into 4th gear around 45 mph and then drop into OD. Temps were fine. It did this all the way to work this morning. We shall see if still holds up on the way back.

Clayzer

P0740 came back!!!! F!!!!

Sig220

The only thing I can think of is the connector at the rear of the engine on the passenger side. It is a multi pin plug that can be disconnected there. I am thinking that if your grounds (like mine) are clean, maybe that connector has corroded terminals. I have not driven my XJ since last weekend, but if I get the chance this weekend I will open it and try to clean it with a metal pick. A long shot I know, but what else have we got?

Clayzer

Fiddled with the NSS again last night and my OD came back. Im guessing it was out of alignment.