OK, so my speedo seems fine and moves along just smoothly until I hit about 55 MPH. That is when the needle starts dancing all over the place bouncing between 55 MPH and 80 MPH like a cracked out jack rabbit.

I was just under the car today pulling the starter to replace it and checked the wiring to the sensor on the tail end of the transmission, and that looks tight. WHAT COULD BE CAUSING THIS??? The Tach is fine and there is no discernible difference in the actual operation of the car.

 

bad speed sensor or bad speedo in dash.

 

How can I single out one or the other? I checked the cost of the sensor and it is 110 dollars. I don't want to replace that and have it turn out to be the actual speedometer. Conversely, I don't want to tear into the dash and have it turn out to be the easier to access, easier to replace sensor.

 

they are like 25 to 30 bucks at rockauto ACDELCO Part # 213194 is 28 bucks

 

Scan tool will tell you. If the reading in the scan tool matchs the speedometer reading the it is the sensor or wiring harness.

I don't like playing the odds game but 90% of the time it is just the sensor.