Expert: Roland Finston - 7/11/2011

Question
QUESTION: A few months ago I started receiving engine code and didn't notice any decreased performance in vehicle. Van has around 130,000 miles. Finally got the codes checked out -- p0700 and p0740. Still didn't notice any noticeable performance reduction. My wife mainly drives the vehicle. But then subtly I noticed that around 45 mph when I would take my foot off of the gas pedal and then reaccelerate, the transmission would feel as it were trying reengage the engine. It was barely noticeable, but I would consider it a slight lurch or lunge. I also became aware that when cruising 60+ mph that it didn't appear that the overdrive lockup was being engaged. We have noticed decreased full economy. The vehicle has no tach to assist in any troubleshooting observations. But I'm sure the TCC is to blame. After driving with no other symptoms -- the transmission seems to fine otherwise and was just serviced last summer with a filter change -- the engine light disappeared. But, the symptoms are still there. That's what confuses me. Why would the engine light code go off, when the problem still exists? I really need to get the vehicle in to perform the basic test on the TCC circuit, I suppose. Still driving the vehicle daily. Is this advisable? Or should I not be concerned? Thanks for your help.

ANSWER: Hi C Douglas,
That issue with the TCC is generally not an issue with electrical connections. About all you can do is check the fluid level in the transmission to be correct. It is possible that a part in the solenoid pack inside the transmission is out of spec or a fluid pump bushing or the torque converter itself may be weakening. But I don't believe that other than a check of the fluid level there is much else that can remediate this, short of removing the trans and sevicing the torque converter or other parts I mentioned. If it doesn't lock up above 45mph it will cause a slight reduction in fuel economy but is doubtful to be so much as to warrant a major repair. The other 'end' of the problem would be if the lockup occurs but doesn't release when you slow to a stop in which case the engine stalls. If that occurs then you do have to service the situation. But absent that I would 'live' with it. Not all transmissions have this lock-up options so you are not in any significant trouble as yet.
Roland
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---------- FOLLOW-UP ----------

QUESTION: Thank you for your reply. I mentioned a filter change last summer. This service was after my wife was driving at the time and the van made a funny 'noise' at a stoplight and the transmission was slipping. She was able to pull into the local high school parking lot and was stranded. The vehicle wouldn't move in any gear. I had it towed to the local shop and even though the dipstick was registering 'full' the transmission was starved of fluid because the filter was so clogged. I'm wondering if there was some wear or damage caused by this event, but after service, the vehicle drove great. The codes and symptoms didn't appear until 6 months later. My question is, should I have the pan pulled and the filter checked again? Thanks.

Answer
Hi C Douglas,
If they can drop the pan, check for debris in the pan, and if none, put the pan back and reuse the fluid, that would be a reasonable thing to try. If you found a lot of debris then that would suggest some parts are wearing out and generally points toward a rebuild of the transmission. However, If nothing abnormal is in the pan, then we really haven't learned anything from that 'exercise'. So why do it?
I would think that if the filter were clogged again then that too would say there is alot of damage going on in the internals of the transmission.
As I said, the alternative would be to drive it and see if it self-corrects/gets worse. The possible causes of the 0740 are 'worn pump bushing or failed a torque converter and both should be replaced OR valve body-lock up accumulator diameter out of spec., possible but not likely'.
So that is why I gave you the advice that I did. If it is driveable and there is only a modest loss of fuel economy you may just want to 'live' with no lock up feature on the converter. Otherwise it is probably $2000 to do a rebuild!
Roland
PS Thanks for the rating and nomination.