First, verify there's a circle around the "D" on the gear indicator in the instrument cluster. That tells us you have the 4-speed transmission and not the hydraulically-controlled three speed. The four speed does in fact have a Transmission Computer. It runs a group of shift solenoids on the front of the transmission. This transmission showed up in 1989 and was used for many years. It was the world's first computer-controlled transmission.
The computer is capable of detecting a lot of electrical and mechanical defects. When it sees something wrong, it sets a diagnostic fault code, and usually puts the system into "limp" mode that allows you to drive slowly to a repair shop without needing a tow truck. Turn the ignition switch off, then restart the engine to get it out of limp mode. As a general rule, if it goes back into limp mode the instant you shift into "drive" or "reverse", it's most likely an electrical problem. If it takes off normally in first gear, then bangs into second gear, especially during or right after an up-shift, it's most likely due to a mechanical defect. Usually it's due to slippage in one of the clutch packs. That's caused by excessive wear in the plates. Limp mode keeps it in second gear. You'll also have reverse, neutral, and park.
This computer was the first one that updates its shift schedules based on wear and driver habits. Older hydraulically-controlled transmissions gave us a couple of years warning that a rebuild was in its future. That was in the form of "shift runaway", meaning the engine would act like it went into "neutral" for one or two seconds during an up-shift. Your computer sees that and as part of its learning, will shift into third gear, for example, but wait a little while before releasing second gear. That overlap maintains the like-new shift feel, but you don't get that couple years of warning that wear is taking place.
An experienced transmission specialist can tell the amount of clutch plate wear by reading the "clutch volume index", (CVI) on a scanner. That's a set of four numbers corresponding to the number of ccs of fluid it takes to apply each of the four clutch packs. Once plate wear reaches the point the computer can't update any more, slippage occurs. The computer detects that by seeing the mismatch between the speeds reported by the input speed sensor, (crankshaft speed) and the output speed sensor, (road speed).
Two things have happened from disconnecting the battery. First, any diagnostic fault codes, (DTCs), will have been erased. That loses that valuable information. Second, the computer reverts back to its factory-programmed values, then resumes updating them as you drive. It can take up to 12 shift cycles or as much as two miles to relearn the current values. Until then, you could have sluggish shifts, or it could bang between gears like a dragster. Most of the time you won't even notice anything unusual.
The scanner can also be used to perform a "quick learn" in the shop without having to drive the car. That's just done for customer convenience. The scanner originally used for this was Chrysler's DRB2. You can find these on eBay for less than $200.00. They use a plug-in cartridge. The year is denoted by the label color that matches the cover color of the service manuals for that year. Newer cartridges will usually work for previous-year models. The best is to look for a yellow "Supercartridge". That's for '94 models and incorporates all of the older individual cartridges for the various models. There was no green '95 cartridge. The '94 one works for '95 models. I can't remember if a different cartridge is needed for transmission work.
I also have the newer DRB3 for all of my vehicles. These are needed starting with '96 models, but with an additional plug-in card called a "Supercard", it will work on all Chrysler vehicles back to '83 models, and it can do emissions-related tests on all car brands sold in the U.S. Starting with '96 models. For that reason, a lot of independent shops bought them. The yellow Supercard works back to '94 models and does the testing on other car brands. You'll need a Supercard with a white label. That works for '83 through '93 models. The last models the DRB3 worked on were some 2008 Jeep models. Repair shops had to upgrade to something newer, so you might find a dusty DRB3 they'd like to sell, or you can find them on eBay too.
Most independent shops have gone to aftermarket scanners now that can be updated, typically for about $1000.00 per year. I have a Snapon Solus Edge for my 2014 Ram. I haven't tried it on transmissions in any of my older vehicles, but it should be able to access every computer on them.
If you weren't having a shifting problem before you replaced the battery, it's likely you don't now. Before we get all "wrapped around the axle" looking for a major problem, I'd start with the basics. A collapsed engine mount can put a half shaft into a bind and prevent it from rotating properly. I've even seen a badly-neglected set of worn brake pads grind into the rotor until they caught and locked up that wheel. The computer can't make up for low fluid level. All kinds of weird things can happen when air gets sucked up into the pump. If the car can be driven at all, and symptoms occur, a fault code should be set that will provide the starting point for the diagnosis. If a code sets just by running the car in the shop, it should specify the electrical circuit that likely has a problem.
Another thing to look for is the shaft in the differential can walk out and catch on the housing. If that occurs while driving, it can crack the housing. On a hoist, you should be able to hear the noise, even when just rotating the front wheels by hand. The repair for that involves sliding the 1"-diameter pin back into place after removing the small, broken locking bolt. I can provide more details and drawings if necessary. This problem has nothing to do with replacing the battery, and won't be detected by the computer.
Monday, January 10th, 2022 AT 6:24 PM
