P0740 Code (a similar story)

[mtmazz]

I have a 2005 Liberty with the 42RLE and I am having the same or a very similar problem as the saga in the following thread from a few years ago:
http://www.jeepkj.com/forum/f196/p0740-******-code-59369/

Here's my story:
Check Engine / Malfunction Indicator Light comes on. Code is P0700 and P0740, which indicates "Transmission Torque Converter Solenoid Circuit Open".
I have replaced the Transmission Solenoid Pack and the Throttle Position Sensor.
Fluid is not (and was not) discolored or burnt smelling before or since the above repairs. No debris or gunk in the pan or filter when removed to replace the solenoids.
The transmission does (and always did) seem to be operating normally, no shift or drivability problems before or since the above repairs.
The Check Engine light continues to come on, with the same codes. After codes are cleared, the light only comes back on after 8-10 miles of steady freeway driving at ~60 MPH. Travel at city speeds or stop & go or varying speed never triggers the fault codes. It was this way before and after the above repairs.

At 188,000 miles if it does turn out to be a mechanical problem in the transmission I'd hate to sink $3000-ish into rebuilding a seemingly perfectly functioning transmission, but everything else on this nearly rust-free vehicle is functioning 100% perfect so at the same time I'd hate to give up on it.

I am debating whether the next step is to the dealer for further electronic diagnosis (which sounds like a dead end based on other similar threads), or to a transmission shop to just have the torque converter replaced (on the assumption that it is the converter simply physically failing to lock after 8-10 miles of freeway driving despite the solenoid telling it to do so). I don't see much sense in rebuilding it completely since there's no evidence of wear or debris inside, but they might try to convince me otherwise.

Has anyone else had a similar experience (P0740 with zero performance problems, clean fluid, and brand new solenoids)? What was the outcome?

 

[mtmazz]

As a follow up: I did read that the normal operation of the transmission is to not attempt to lock the torque converter until after several miles of sustained highway speeds, so that makes sense with what I am experiencing. The fault code is triggered after the converter is supposed to have been sent the lock signal by the computer and a difference of 200+ RPM is detected between the engine speed and transmission shaft speed (or so I read).

So I still don't know whether it is an electronic problem or the actual torque converter itself (like is the electronics not signaling the converter to lock, or is it signaling but the converter is not actually locking), but at least that tidbit of information helps confirm the diagnostic process so far.

 

[HoosierJeeper]

The torque converter clutch is actually what fails...it slips, not necessarily failing to lock up. As the transmission heats up, the slippage becomes more prominent. Are you sure there isn't any clutch material in the pan? Mine was loaded up. Had 150k.

I would take it to a shop and have the Clutch Value Indicies read. That'll tell you the exact condition of all the clutches. My TC one was bad, and the 2nd gear one and reverse one were all bad as well, despite it driving normally, so I went ahead with a rebuild.

Has yours gone into limp mode at all? Mine would on very hot days or when towing.

 

[JasonJ]

A Master Rebuild kit is priced from $200-$250... another $250 or so for a new torque converter.. makes you wonder if it's easier/cheaper to just get as low a mileage used trans from a parts yard or to rebuild the one you have.

Thankfully, a rwd/4wd trans like these in the KJ is fairly straightforward to R&R.