Why does a 2001 Jeep Grand Cherokee automatic transmission stays in first gear and not shift into 2nd gear?

Answer 1

One cause is an improperly adjusted rear band in the transmission. The transmission goes into "limp mode" if the band is out of adjustment too far. This is a mode which protectsthe tranny from further damage by keeping it in 1st gear. An improperly adjusted band can cause the shifts to be either too hard slamming into the next gear or too soft causing it to slip. The rear band in the transmission is located inside the bottom of the transmission. You must take the transmission oil pan and filter off to adjust the rear band. I have seen many different adjustment specs, but what worked for my 2004 Laredo with a 6 cyl and 42RE transmission was to loosen the lock nut on the band and then tighten the 1/4 inch adjuster bolt that is in the center of the lock nut to 72 inch pounds. NOT Foot Pounds. Then back off the 1/4 " adjuster bolt 3 5/8 turns and then re-tighten the lock nut. This smoothed out the shifts and my tranny stopped going into "limp mode". The pressure sensor and pressure solenoid are also located in the same area and can be changed very easily when you are in there. Many times the pressure sensor and/or solenoid fail and throw error codes to the service engine soon (SES) computer system. You can buy them both new on e-bay for $105. I'm sure there are many other causes of a tranny going in to "limp mode", but this is at least one of them. Unless your tranny fluid has been changed recently it is a very good idea to change the fluid and filter since you already have to drain it.