If the transmission in your Jeep Grand Cherokee does not downshift, you most likely have an issue with the shift solenoid. Unfortunately, this is a moderately difficult repair procedure because the solenoid is located inside what is arguably the most complex piece of equipment in your Jeep: the transmission. The transmissions used on the Cherokees, such as the ones made from 1984 though 2001, have the solenoid located inside the transmission oil pan.
Open the drain plug on the transmission oil pan with a socket and drain the oil into a drain pan.
Remove the bolts that secure the transmission oil pan to the transmission.
Remove the bolt that holds the transmission dipstick bracket to the bell housing with a socket. You can locate the bolt from the engine compartment.
Place a scraper between the transmission pan and the bottom of the transmission and break the seal loose so you can remove the pan.
Remove the defective solenoid by removing the bolt that secures the solenoid to the harness. Three solenoids control the shifting on the Jeep. All have white and yellow wiring harnesses connected to them. The solenoid to the left (towards the Cherokee's engine) controls shifting "overdrive." The solenoid in the middle controls shifts between second and third gear. The third solenoid, closest to the rear of the Cherokee, controls shifts between first and second and between third and fourth. If you know which gear your transmission is stuck in, replace the solenoid that corresponds with that gear. If you are not sure, remove all three.
Disconnect the wiring harness from the solenoid(s) by pulling the harness off the solenoid. Make note of each wire and where it connects if removing more than one solenoid.
Slide the new shift solenoid(s) into place. The new solenoid has a ground wire. Secure the wire to the bolt that secures the solenoid into place.
Reconnect the wiring harness to the shift solenoid(s.)
Scrape the old gasket off the transmission pan and off the mating surface of the transmission with a scraper.
Place the new gasket onto the mating surface of the pan and secure the pan back to the transmission.
Secure the transmission dipstick tube to the bell housing.
Place three quarts of transmission fluid into the dipstick filler tube.
