What is the socket size to remove the speed sensor?

Hello, the nut on the sensor should be around 1", which is around 25mm. A deep well 12-point socket should work well enough.

William

You have the world's first computer-controlled transmission, commonly called the "A604". In later years, the industry tried to standardize some things, including transmissions. Your transmission could be listed as a "41TE". That stands for four speed, light duty, transverse-mounted, electronically-controlled.

A 2009 model doesn't use the same transmission or parts. What's happening is your Transmission Computer has detected a problem, set a diagnostic fault code, and put the system into "limp" mode that allows you to drive slowly to a repair shop without needing a tow truck. Limp mode keeps it in second gear, but you do still have reverse too.

The place to start the diagnosis is by having the diagnostic fault codes read and recorded. Since staying in second gear uses more fuel, it increases tail pipe emissions. That means the Check Engine light should be on. Older code readers could only read fault codes in Engine Computers. In this case, the code will simply say there are other codes to be read in the Transmission Computer. Typically, you need a scanner for that, but you can start this yourself by following the instructions on this page:

https://www.2carpros.com/articles/retrieve-trouble-codes-for-chrysler-dodge-plymouth-odb1-1995-and-earlier-car-mini-van-and-light-trucks

You cycle the ignition switch from "off" to "run" three times within five seconds, without cranking the engine. Leave it in "run", then count the flashes of the Check Engine light.

I should stop here a minute and clarify something. A code in the Engine Computer telling you there's other codes in the Transmission Computer might not apply to a '94 model. That may have started with '96 models when they went to the newer emissions system. All that means is there may only be a fault code in the Transmission Computer. I would start by asking at some local auto parts stores. If they can read your codes, they do that for free, but be aware, they're in the business of selling parts. No fault code ever says to replace a part or that one is bad. About half of the time the cause of the code is related to a broken or grounded wire, a corroded mating pair of connector terminals, or a mechanical problem related to that part. If you tell me the exact fault code number, I can find the definition for you and suggest how to proceed.

Yup, they're all two-digit codes. The first digit will be a set of flashes equally spaced, then a short pause, then the second digit flashes the same way. There will be a longer pause, then the next code, if there is one, will flash the same way. After another long pause, the last code will be code "55". Five flashes, a short pause then five more flashes. Code 55 just means "end of message". It's done flashing codes. On my '94 Grand Voyager, if you think you miscounted the flashes, just turn the ignition switch to "off", then back to "run", and the sequence will repeat. When you turn the ignition switch all the way to crank the engine, that is what takes it out of "test" mode and the flashing stops.

I'll be back about this time tomorrow to see how you're doing.

I forgot about code 12. What I saw was code 12, then code 55. Both of those can be ignored. I like to say, "bail out and duck for cover!", But it's really nothing to pursue. Code 12, depending on where you read the definition, means 12-volt power was lost to the Engine Computer. In other words, you turned the ignition switch off. Code 55 means it's done flashing fault codes. Here's how they're shown on our list:

12 - Memory to controller has been cleared within 50-100 engine starts.
55 - End of message.

Where code 12 becomes useful is when you have an intermittent stalling while driving problem. Most often this is due to a failing crankshaft position sensor, or to a lesser degree, a failing camshaft position sensor. Signals must be received from both of them for the Engine Computer to know to turn on the automatic shutdown, (ASD) relay which sends power to the ignition coil pack, injectors, alternator field, fuel pump, and other places. These two sensors are responsible for roughly 95 percent of intermittent stalling issues.

It's when we don't find a problem with those two circuits that we need to look at other possible causes. The idea here is we would start the engine, then erase the fault codes, including that code 12, then go out on a test drive. There's two ways to approach this, but both require a scanner or at least a simple code reader. Once the stall has occurred, it's important to not turn the ignition switch off as that will automatically set code 12 again. Instead, we want to read the codes that just set, if any, during the stall. If code 12 is set, that tells us to look at the 12-volt feed circuit to the computer. That includes the ignition switch, connector terminals, and wiring. If code 12 did not set during this event, that rules out one circuit from the list of suspects.

The better approach is to use a "record" feature found on most high-end scanners. You drive with the scanner connected and set to record mode. When the problem, the stalling in this case, occurs, you press the "record" button. That captures up to about five seconds of data that you can scroll through slowly, later, to see what changed or which signal dropped out. Because that data travels through the scanner's memory, the recording actually begins a couple of seconds before you pressed the "record" button.

After looking through the list of fault codes, I did see there is nothing on a '94 model to indicate you need to read codes in the Transmission Computer. You will have to find someone with a scanner to do that for you. You can ask at some auto parts stores, but your van might be too old for their equipment. Another option is to visit a community college with an Automotive program. They will have some scanners that work on '95 and older models.

Be aware that for now, it is important to not disconnect the battery or let it run dead as that will erase the fault codes, then that valuable information will be lost. If that does happen, you simply need to drive the van until the problem occurs again. At that point the code(s) will set again and can be read.

Let me know when you have those code numbers. As another hint, it can be very helpful to know exactly when a code sets, or in this case, bangs down into limp mode. For example, if you start the engine right after erasing the codes, and immediately you see on the scanner that one or more of them set again before you even shift out of "park", it has to be an electrical problem. We'd expect to find a grounded wire, corroded connector terminals, or a defective solenoid in the solenoid pack.

If no code sets until you shift into "drive", the problem involves something that turned on at that time. We'd look at pressure sensors and the fluid circuits they monitor.

By far, most problems show up during or right after a shift from one gear to the next. Since the 1950s, Chrysler has been the world's leader in innovations that benefit car owners. Among those was your transmission design. It was the world's first computer-controlled transmission with the ability to learn driving styles, and to update for internal wear. That did present a new problem, however. More on that in a minute. All automatic transmissions have multiple drums with stacks of clutch plates inside. When one of them is released, no wear takes place. When they're locked up solidly, no wear takes place. It's in between, when they're going from free spinning to locked up that a little wear does occur. For decades we'd feel that as sluggish up-shifts, or "engine runaway" during a shift because it took too long for the clutch plates to fully engage. That gave us two or three years warning that a rebuild was in its future.

Your Transmission Computer learns the volume of fluid it takes to make each clutch pack lock up. As the plates wear down, it takes more and more fluid to fully engage that clutch pack. Instead of allowing that engine runaway to occur, through learning, the computer will engage third gear, for example, then wait just a little longer before it releases second gear. That extra few milliseconds is all it takes for third gear to be fully engaged when second gear is released. What you feel is a nice crisp shift like when it was new, ... Until the day comes that it can't update enough to overcome the wear. That is the day excessive slippage occurs, usually during an up-shift. That slippage gets detected, the appropriate fault code is set, and the computer puts it into limp mode / second gear. The only way to get it out of limp mode is to stop, turn the ignition switch off, then restart the engine. You had no warning this was about to occur.

When you do have that excessive clutch pack wear, the fault code definition will refer to "gear ratio error". There's an input speed sensor, meaning crankshaft speed, and an output speed sensor, meaning road speed. The computer knows that for a certain input speed, and knowing the gear ratio, road speed has to be a certain value. When those two don't agree, it's due to slippage in that clutch pack.

Another way a transmission specialist diagnoses this is to look at the "clutch volume index", (CVI), on a scanner. That is a set of four numbers corresponding to the volume of fluid it takes to apply each of the four clutch packs. I don't remember what "normal" is, but as an example, one of them might require 40 ccs of fluid when it is new, and by the end of its life, take 120 ccs of fluid. The specialist has those values memorized. If that clutch is shown close to 120 ccs, he knows it is as worn as it can get. On the other hand, if he sees it is listed as needing 80 ccs, he knows he needs to look at other suspects besides that clutch pack.

Since I mentioned the ignition switch, I should add they did have a lot of trouble with them, but not as far as stalling or loss of engine power. There's actually three or four separate switches built into the ignition switch. The one that caused the trouble was for the accessory circuit, meaning the radio, power windows, wipers, and heater fan. The people who had the most trouble we those, like my mother with her '95 Caravan, who commonly switch the ignition switch on and off while the heater fan is set to one of its higher speeds. That causes a lot of arcing across the switch contacts that leads to overheating and failure. I've addressed that over a dozen times, and I'll be happy to do that again, but it needs to be on a new, separate question just for that topic.

Another thing to consider, if a fault code suggests a wiring problem, is to look at the fat wire harness that runs along the left inner fender and disappears under the battery tray. That harness can slide back and forth as the engine rocks between accelerating and coasting. That will result in wire insulation rubbing through, along with the paint rubbing off, then bare wires touch bare metal. A coworker ran into that causing an overheating problem due to a blown fuse link wire for the radiator fan. The clue turned out to be the backup lights quit at the same time. The burned fuse link wire was a repeat failure three or four times with an elusive cause until the backup light issue was noticed. I don't know if transmission wires travel through that harness too, but it's worth a mention.

As long as I'm at it, let me point out one more characteristic with this transmission. That is the need to do a relearn after the battery is disconnected. Those CVI numbers, and all the other learned data is lost. The next time the vehicle is driven, we're told it can shift like a race car, (very harsh), or very sluggish. It can take up to two miles and / or 12 shift cycles to relearn data. My experience has been it's almost impossible to notice anything is different. They seem to shift just fine. Some scanners now also have a relearn procedure built in that cycles the transmission through all its gears while you're standing still. That eliminates the need for a short test drive after some service procedures are completed.

When you have some fault code numbers, I'll look up the definitions, then we'll figure out where to go next.