Probably the speed sensor on the transmission.
Correction; that should read "Idle speed motor" I thought this translated to an important question I didn't see here: "How do you replace a speedometer on a Jeep Grand Cherokee?" Mine, in my 1993 Grand Cherokee, has not worked properly for two years and a speedometer shop tried but couldn't fix it. I've been using my Tachometer to estimate MPH. Apologies to the original poster if the correction is yours. And sorry to everyone else since neither of these are answers.
You do not fix it you just replace it.
To fix the speedometer on a 1978 Jeep CJ7, first check the speedometer cable for any damage or disconnection, as this is a common issue. If the cable is intact, inspect the speedometer head itself for any signs of malfunction or wear. You may need to remove the speedometer from the dashboard to clean or replace it. If the problem persists, consider replacing the speedometer cable or the speedometer unit entirely.
Most likely speedometer cable
How to change the brake switch on a 2004 Jeep grand Cherokee Laredo
I paid $350 at Canadian Tire to fix the A/C in my 2001 Jeep Cherokee sport.
blend door failure is a common problem on 97+ Jeep Cherokee
how do i fix my 1998 jeep grand Cherokee when the wheel turns right it locks up and I cant turn it back. If I put it in reverse it will unlock and I can drive again.
Code 13 is no vehicle speed sensor signal. Check/replace the speed sensor on the tailshaft of the transfer case.
Yes, replace it.
how to fix or check po 206
You probably need to buy a new gasket for it.