1998 Dodge Caravan speedometer jumps up and down trany drop

POCKETBOY

MEMBER
1998 DODGE CARAVAN
6 CYL
FWD
AUTOMATIC
22,000 MILES

I have a '98 dodge caravan 3 Liter with 220,000 mi. On it. The "service engine soon" light came on a couple of weeks ago and the speedometer went goofy. I'll be on the road at about 45mph when the speedometer will drop to "0" then jump up and down. Then the transmission will drop into 2nd and stay there for a while occasionally going back up into
drive. Back and forth as the speedometer jumps around. I talked to the local trany people and they said that they didn't think that the problem was with the trany?

I removed the positive wire from the battery, replaced it and it seemed OK but soon did the same thing. I removed the air intake and sprayed carb cleaner in the intake while the engine was running. There again, it seemed OK but soon did the same thing.

Can you tell me what is going on?

1 Reply

CH112063

MECHANIC
1,320 POSTS

Yeah, the two sensors on the transmission feeded information to the transmission controller for tachometer and shift information. Input and output. There both together midway in the center line of the trans. But the vehicle speed sensor was used for the speedometer. These three, must be working. It was usually the vehicle speed sensor that caused a misinformation sense that the TCM would think was slippage. This turned off the transmission controller. The VSS is in back. You'll see it down in the back in the axle area. Its where the right side axle entered the trans. It got the most wear. Ok change the whole unit.10mm screw.
Then disconnect the battery, wait a minute and reconnect. Use the negative terminal and be careful to do it when it's a cold engine. This gear reduction(2nd only) is called a transmission limp-in mode. Ok High mileage. I hope that the trans is not slipping. Check the fluid when its running, in park, hot.