I was working on the transfer case and didn't get the speedo hooked up right so it wasn't against the gear. No big deal, easy fix. What I am wondering is why would the speedo throw a check engine light. What is the purpose? Does the speedo's operation effect anything else? I can't figure out the purpose of having the engine light come on for that. Any thoughts?

 

What was the code number/description?

 

Yep, I've had two speed sensors go out and both times the engine would spit and sputter. The PCM adjust the engine's output by the speed sensor.

 

When I got my XJ, the speedo sensor went out a month later. It threw a code that "Speedometer sensor not detected". The only thing that was effected was my speedometer gauge, which just sat at 0. No difference in performance or drivability

 

My engine seems to be running OK. Thats what I was wondering. If the speedo sensor did more than just move the gauge. I guess adjusting output is to save fuel?