Texoma

My daughter bought a 2000 jeep grand Cherokee 4.0 automatic. The transmission has 1st 2nd [D].
Putting it in D, you can start out in first, shift into 2nd and it wants to keep climbing in rpms and not shift any higher. The od button on the shifter makes the button on the dash work. If you gas it and let off and rev it some it will finally shift up.

You can also manually start in 1st, manually goto 2nd and when you manually shift to D it doesn't want to shift into D.

also... braking .. sometimes when braking gently at a slow speed the vehicle feels like it's moving up and down.. let's say at 5mph... gently press the brake and allow the tires to roll slightly... no vibration while driving... other times while going faster and braking shudder in the steering wheel occurs.

no cel is on(light works but doesn't remain on)

I hooked up my code reader(elm) to the odb2 port and it connected to the ecu but cannot read data.S.

Any help is appreciated.. First time with a jeep..

Texoma

No jeep experts?

peep

The transmission has internal solenoids which control shifting. May need replacement.
However, the switching my be hampered by dirty trans fluid and accumulated debris, blocking the filter starving the input to the pump and reducing trans pump output pressure.
With a 2000 jeep, a fluid change can't hurt. ATF4 fluid, the filter change is optional as most are just a screen. But since the pan is off, change the filter, comes with fresh gasket.
Neoprene gaskets can be reused, cork gaskets are one time use. Don't overtighten the pan bolts.
This is a cheap fluid service relative to cost of a trans overhaul or replacement.