(actually a '98 Plymouth Grand Voyager, but same difference.)
My Plymouth Grand Voyager is giving evidence of what I think is a subtle transmission issue. At highways speeds, every now and then there is a subtle ‘grab’ or ‘skip’: it could be mistaken for simply roughness in the road, but it happens on smooth road, and isn’t exactly a rough-road feel.
I’ve read some of the discussions, related to computer causes. I’m wondering if there are other causes for this kind of problem, and whether this is an early symptom of something more serious on the horizon.
The car has been well-maintained, esp. in terms of fluids (oil, transmission fluid).
The car has 125K miles, and I am the original owner. The car has spent its entire life in California, and so has been free from exposure to a lot of freeze-thaw, and road salt.
The computer which manages the cab environmental controls has some display (but not function) issues, which I don’t think are relevant to the transmission problem (but might be). The ABS light is on continually, which a dealer told me was a false light, but a few weeks ago I braked hard and the ABS ‘chatter’ did not occur, and the brakes locked. Absent a computer problem, I believe the ABS issue is separate from the transmission.
Sounds like the torque converter. What type of fluid is in the transmission? When was it (and the filter) last changed?
well maint. is important, try taking to local shop and have it checked for leaks, im in the oil change buisness and i see alot of these same issues in every dodge caravan ive seen, 9 times out of 10 there is a leak where the wiring harness inters the transmission, witch would eventually make the fluid level low enough to act up but still drive. if this is not the case than i would recommend seeing a trans specialist for 2nd opinion.
not sure of what type of T-fluid, but everything was checked three weeks ago. Oil and filter changed then, too. Wasn’t aware of a transmission filter…?
In trying to diagnosis this problem, you have to make sure this is not a driveability problem before you suspect the transmission i.e. is the engine having a problem producing smooth power. It would probably be good to scan the power train control computer to see if there are any codes set. The codes set may not have turned on the check engine light. If this comes up dry, a transmission technician can scan the transmission data to glean any likely candidates for the trouble.
Get back to us if you get any further on this situation.
Well, it turned out to be the ABS system, and the computer/sensors associated with it. At least, that seems to have fixed the problem.
Tangentially, can anyone tell me WHY this car had at least two (if not three) onboard computers (EEC, ABS, and I think environmental), and why the parts cost for replacement is $600-700? I used to design processes for building the EEC chips for Intel, and 1) the parts maybe cost $20 retail, and 2) I can’t believe the packaging costs almost $200 (assuming a 3X markup).
What you explain could also be caused by the wrong type of ATF in the tranny. Make sure they have put ATF +4 in the tranny, if not flush and change and see if it gets better. Don’t buy the additive story that they will tell you makes regular ATF equal to ATF +4.
thinking about your question, and simplifying… The main engine control computer has to do an extensive table lookup and make decisions for every combustion. That comes to about 1ms per decision, with hundreds if not thousands of table lookups and calculations for each.
There are 2 choices for this design, you can use a dedicated computer to do this, running only the one task, or you can have a fast computer doing this task as part of a multitasking operating system which also performed the ABS function, the temperature control, the security control, and your navigational system.
In other words running Windows! or UNIX!
I think I would rather have the dedicated computers.
Now the parts cost is another question. When i was in the testing business, I remember the very complicated tests the components had to withstand to ensure they would operate in the automotive environment, with 10kV spikes, Power jumping from 12v to 40v (load dump), temperature extremes, etc. This is part of the cost, the rest is in the volume, not high.
Another part of the cost is the sealed metal enclosures for the computers, and the expensive connectors, to protect against contamination from fluids, etc.
thanks, good advice, I will check this out.