yes, in 98 its s service engine soon, (SAE its MIL) but the check engine light on
this car is OBD2 compliant. if the lamp is out , all is ok , driving.)
(cept in canada where their laws allow misfire and no light,etc, but you never disclosed the country)
my guess is its a 4speed auto. ?
have you seen the FSM reasons list for harsh shifts ?
1: move the P/S switch to S. (standard shift = softer)
2: is the OD lamp stuck on or flashing, that too is a warning
3: and pull the DTC codes ,
btw some tools cant see all A/T codes ,so the autozone cheap tool may miss some.
but of lamp is off driving in USA, there are no codes
but there are what is called pending codes.
only a full scan tool can see them.
the pending are of 2 types.
1: under the Radar. (some DTCs take 2 or more fails to store)
not using a real scan tool invites you being blind to what truth/
btw if the tranny drops to LIMP home , you dont get 4 gears, you get 2 or 3.
and guess what, it shifts harder.
the tranny has its own VSS , if that fails (code) it drops to speedo VSS
and again will shift funny.
the 4 speed is complex.
see my page on 4sp
btw they moved your TCM inside the ECU.
Slush pump diagnosis
dont know which you have.