The water pump in our six cylinder 1997 Dodge Caravan failed on the road and had to be replaced. When I picked up the car, it seemed fine, but a day later, the car suddenly downshifted as I was merging onto the parkway and hung out in second gear for the next 15 miles. I dropped it off at my mechanic’s, and he ran a computer diagnostic that showed transmission errors. He recommended replacing the electronic unit at a minimum, possibly the whole transmission. He didn’t charge me for the diagnosis, but wiped the record, so I can’t tell you what the codes were. When I picked the car up, however, it ran fine and has for the past six months, though we have put only 1,200 miles on it, as my wife is afraid to drive it. The car has 130,000 miles on it and needs tires, but we have kept up with the maintenance, so it has a lot of new parts. Should I keep this car? What should I do to make sure it is safe before taking it on a trip?
Second gear is "limp" mode that lets you drive slowly to a repair shop without needing a tow truck; definitely not at highway speed. Rather than stress the engine for 15 miles, simply turn off the ignition switch, then restart the engine to get it out of limp mode.
In general, if it goes to second gear as soon as you start the engine and shift to "drive", it's a sensor or other electrical problem that was detected by the Transmission Computer. If it starts out in first gear like normal, then bangs down to second gear during or right after an up-shift, it's most likely slippage in one of the clutch packs. That requires the transmission to be rebuilt.
There's a third, relatively uncommon cause for going to limp mode that could be related to the water pump depending on which engine you have. Unlike older hydraulically-controlled transmissions, your computer watches how much volume of fluid it takes to apply each clutch pack. It uses that information to determine the amount of plate wear and to adjust clutch application to overcome the normal slippage that takes place during the overlap between one clutch applying and one releasing. That results in a nice crisp shift just like when it was new, ... Until the day comes when there's too much wear to overcome. The wear doesn't take place any faster than in older transmissions. You just don't have the two or three years of sluggish shifts to alert you that wear is taking place. Instead, it shifts fine one day, then goes to limp mode the next day.
If your mechanic had to disconnect the battery to replace the water pump, those learned values in the computer were lost from memory. They are relearned beginning with the next time it is driven and could take a few days for the computer to relearn your driving habits and the clutch pack wear. Until then it reverts to values pre-programmed at the factory. Since there's obviously more clutch wear than when it was new, some slippage will take place during an up-shift. When that slippage is detected, it goes to limp mode. The fact it hasn't acted up again in 1200 miles suggests this is all that happened.
There's an easy way to determine how much clutch pack wear has taken place. Visit the dealer or any transmission shop that has the Chrysler DRB3 scanner. It will access the Transmission Computer and read out the "clutch volume index" (CVI). That is a set of four numbers corresponding to the volume in ccs of fluid it takes to apply each clutch pack. Based on those numbers, an experienced transmission mechanic will know how much life can be expected to be remaining before the transmission will need to be rebuilt.
Chrysler was the first manufacturer to develop a computer-controlled transmission. It was first used in 1989. If your wife is afraid to drive the van because of that little hiccup, you'll have to buy a car with a manual transmission because almost all automatics are computer-controlled now.
July, 28, 2011 AT 12:50 AM
Thank you for a clear analysis. I will take your advice and see if one of the local dealerships can give me a life expectancy for this transmission.