Chrysler Repair: Tranny issues follow up, torque converter clutch, torque converter clutch circuit malfunction

Question
Roland,
Basically what are your thoughts on how long I can run the vehicle with this condition, I don't want to run it to the point where the trans goes into limp mode or worse prior to being able to trade it in via the "cash for clunkers" program.  In order to use the program the vehicle must be in running condition.
Thanks again.


I have a follow-up to a question to one I posted about four weeks ago (see below).  I've
driven the vehicle for about 800 miles since and still show no signs of drivability
problems.  Can I run this indefinitely “as-is” or is it just a matter of time until this
cascades into a bigger problem (i.e. am I doing additional (more costly) damage driving
the vehicle this way?)  Like I said before I don't want to invest $$ in this vehicle and
have started looking for a replacement but based on my luck so far it going to take some
time.  My concern is since I can’t trade it in with the engine service light on if I
continue to drive the vehicle and it becomes ‘un-drivable’ then it won’t qualify for the
CARS program and then I’m completely out of luck.  Thanks in advance for your time.
Regards,
John

Question
Roland,
I have a 2001 Chrysler Town & Country with a 3.8 liter engine and 105,000 miles on it
that is giving off the following diagnostic codes (P0700 Transmission Control System
Malfunction) and (P0740 Torque Converter Clutch Circuit Malfunction). I don’t have any
noticeable drivability or shifting issues just that the service engine light has just
illuminated. The vehicle has been regularly services including two transmission flushes
(the last being at 100k). I don’t want to invest a lot of $$ in this car and based on
these codes I'm sure it can be a multitude of problems but any insight you could provide
would be appreciated.

Answer
Hi John,
The torque converter has a lock-up capability which comes into play when the vehicle is
going  about 35 MPH or so and which you would notice as a slight slowing down of the
engine as if the gear has shifted up about a 1/2 step. This produces a bit more economy
of operation and less heating of the trans fluid and some braking action when you release
the throttle. But it isn't crucial to the operation of the vehicle. It is hydraulically
controlled by means of the solenoid on the torque converter clutch and solenoid pressure
switches in the valve body that feed fluid to the clutch. It is possible that there is
some dirt/malfunction in the valve body regarding the pistons that regulate the hydaulic
pressure to the clutch on the torque converter so removal and repair/replacement of the
valve body could re-establish the lock-up function. That would be a somewhat costly
repair, done by dropping the oil pan and removing the valve body only, but much less
costly than removal and replacement of the solenoid on the torque converter itself which
would require removal of the transmission.
I would not recommend doing either at this time. Rather, wait until some more serious
issue with the trans which requires overall rebuild at which time the torque converter
problem could be simultaneously corrected would be prudent.
Roland
PS The 0700 merely is noticing that another specific code has been logged into the
memory.

Answer
Hi John,
My understanding is there should be no limit as to how long to run without torque converter lock-up. Many transmissions over the years had no lock-up and that feature came in relatively recently as a means for increasing fuel economy. So my inclination would be to wait. The loss of efficiency/fuel economy is in the range of 5%.
Roland