What will happen if my speed sensor goes bad in my transmission?

Question

I have a 1998 Plymouth voyager. It has 191,000 miles on it. I have never had any transmission trouble with it. It recently started acting up. It never jerked or anything before, just a sudden onset. It is sort of downshifting and won't change out of low gear. When you are driving the rpm will run up to about 3000 to 3500 then the speedometer will drop to 0 and flop back and forth then go back to where it should be. The fluid, filter, and gasket were all changed but it did nothing to help. I live in a very rural area and would have to have it towed to a shop which would cost at least $80.00 and then $60.00 just to have it scanned just to see what the problem is. I can't afford to spend that much on the vehicle. I guess what I'm asking is how like do you think it is that it is the speed sensor, or what else it could be. The speed sensor is around $50.00 and my husband is capable of putting it on. Again I don't have the money to take it to a shop at the moment and my husband is capable of doing the repairs, I just need to find a good guess as to what the problem is. Thank you for ANY help you may have.

Bethany

Answer 1

Here is what happens when the Output Speed Sensor goes out on a Chrysler minivan:

The Check Engine Light illuminates with P0700 General Transmission Fault code.

The speedometer stops working.

The transmission defaults to "safe mode", locking itself in 2nd gear.  

The sensor is easy to replace and if your husband can do it more power to him.  The Check Engine light will probably remain on though until the code is cleared.  

Answer 2

On a computer controlled engine any one of several input sensors can go bad over time, so you need a scanner to plug into the OBD II outlet to see what is going on. Just replacing parts is just guessing. Maybe you can talk a mechanic into coming to you for a diagnostic check.