One thing you can watch for is WHEN it bangs into second gear. As a general rule, if it starts out in second gear right away, or if it suddenly shifts down to second while you're cruising at a steady speed, it is most likely sensor-related. If the shift to second occurs during or right after an upshift, especially under load, it is more likely to be caused by clutch pack slippage. There is an input speed sensor watching crankshaft rpm and an output speed sensor watching axle speed. Based on the final drive gear ratio that is programmed into the transmission computer, it knows that when engine speed is a certain rpm, the axle had better be turning as fast as it expects. When the two don't correlate, the computer knows there is slippage taking place in a specific clutch pack. It will go to limp-in and set the appropriate diagnostic fault code in memory. You already figured out that you have to cycle the ignition switch off and back on to reset the computer, but those fault codes will remain in memory. It's important to not disconnect the battery or let it run dead or those codes will be erased and that valuable information will be lost.
For your viewing pleasure, here is a partial copy / paste version of a reply I posted a few days ago that will provide some information on how this transmission works:
Chrysler was the first to use a computer-controlled transmission in the 1989 models. GM thought so much of it they wanted to buy the rights to build it but they ended up designing their own. Other manufacturers have followed suit.
For reference, it used to be called the A604 transmission but it's the same piece even though the name has changed. Under the new designation, the 41TE stands for 4 speed, light duty, transverse, electronically controlled.
As a point of interest, when the clutch plates wore down on older hydraulically-controlled automatics, the shifts became sloppy and occasionally there would be "engine runaway" where the engine would speed up momentarily due to slippage during the upshifts. You had years of warning that the wear was taking place. Eventually you decided it was time to have it rebuilt. One of the features of the 41TE is the electronic automatic transmission controller (EATX), knows exactly how many ccs of fluid volume it takes to apply each clutch pack. As the plates wear thinner, it takes more fluid volume to fully apply the clutch. Those four numbers can be read out on the Chrysler DRB2 or DRB3 scanners and on some aftermarket scanners. They are called the "clutch volume index" (CVI). Based on those numbers, an experienced mechanic can tell how much wear has taken place in the clutch packs and he can provide an reasonable guesstimate on the remaining amount of life.
As the plates wear, the computer notices it takes more fluid to apply the clutch packs. To prevent that slippage and engine runaway during upshifts, it begins to send fluid to one clutch pack just a little sooner before it releases the previous gear. That updating causes it to shift solidly just like when it was new, ... Until the day comes when it can't update any further. That's when the slippage occurs and the computer can't overcome it. The advantage is you always have crisp, solid shifts. The disadvantage is there is no warning when problems are going to occur.
There are two speed sensors in the transmission. The input speed sensor measures engine crankshaft rpm and the output speed sensor measures half shaft rpm. The gear ratios are programmed into the computer so based on which gear it has activated, for any given engine speed it knows how fast the half shaft had better be going. If the two don't agree, due to slippage or a defective sensor, the computer defaults to "limp-in" mode. That's where it stays in second gear to allow you to drive it slowly to a repair shop. The solenoid pack is spring-loaded to allow operation in second gear, but you can also use neutral, reverse, and park. You must cycle the ignition switch off, then restart the engine to get it out of limp-in.
There is no speedometer cable. Tire size must be manually programmed into the computer. With that information and half shaft speed, the computer calculates road speed and sends that information to the instrument cluster which is a computer in itself.
The first 100 of these transmissions were hand assembled and worked perfectly. Once they started to mass produce them on an assembly line, a lot of problems developed due to "tolerance buildup". That's where every part had a specification for some dimension, and a tolerance, or how much it could be off and still be acceptable. When enough parts were off, such as a sealing ring being off-center a little one way, and the sealing surface on the mating rotating shaft is off the other way, after some wear takes place, the two parts might move away from each other enough to cause some internal fluid leakage, and slippage. To resolve those problems, there have been a ton of updated parts produced by Chrysler and by the aftermarket repair industry. For that reason, a replacement rebuilt unit from Chrysler was a good deal because it included all of the latest and best parts. Rebuilding your old transmission with those new parts got fairly expensive. Plus, many mechanics didn't bother to check or adjust those tolerances. If they just threw in new plates and seals, you could expect to have the same problems in a few years. In that respect these transmissions have gotten better so now a bigger percentage of problems are caused by the two speed sensors.
A real fast way to tell which transmission is in the vehicle is to look at the shift indicator in the instrument cluster. When the 41TE is used, there will be a circle around the "D" indicating it is the overdrive model. In the first few years, this was also called the "Ultradrive" transmission.
Special transmission fluid is needed in this transmission. Using the wrong stuff won't damage it but it will cause a chatter when the lockup torque converter engages at around 33 mph and in 3rd or 4th gear. It is referred to as a shudder. An easy way to identify that is to hold the gas pedal steady to maintain a steady road speed above 33 mph, then lightly tap the brake pedal for an instant. That will trigger the torque converter to unlock. It will relock in about two or three seconds. If you feel the shudder each time you do that, suspect the wrong fluid is in it.
You will also hear a ratcheting sound for one to two seconds when shifting into reverse or drive, and when slowing down to a stop. That is the shift solenoids clicking on and off to modulate the engagement of the clutch packs so they don't bang into gear. Older hydraulic transmissions used accumulators that had to fill up with fluid relatively slowly before the fluid pressure would build up enough to apply the clutches. That ratcheting sound is the computer doing electrically what the older transmissions did mechanically.
The computer is also capable of storing diagnostic fault codes. They will indicate the circuit or system with the problem, not necessarily the defective part. Codes from the Engine Computer can be read by simply cycling the ignition switch and watching the odometer display or the flashes of the Check Engine light, but a scanner is required to read codes from all of the other computers including the EATX.
As a final note, when installing a rebuilt transmission from Chrysler, they will only warranty it if the cooler in the radiator is flushed out too. There are special pumps and cleaning fluids for that purpose. These transmissions are very touchy when it comes to debris circulating in the fluid, unlike their tough older three speed transmissions. You could rebuild those in a sandbox and still not have problems.
Sunday, December 5th, 2010 AT 5:06 AM