Limp mode what causes limp mode?

Yes, that is the whole idea of Limp Mode. It limits you to first and second gear so you can limp slowly to the nearest garage without causing catastrophic damage to the engine. What you need to do is connect a good quality DTC code reader scan tool and see the real reason that Limp Mode has been engaged.

https://www.google.com/search?q=1999+jeep+cherokee+limp+mode+causes

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Limp mode stops when the problem that caused it is repaired, which you have not done yet, whatever you did was not the problem that forced the vehicle into limp home mode keep doing the diagnostics and fix it right.

Limp mode is triggered by a serious issue with the cars transmission or engine controls.

Most limp modes are caused by transmission faults but can be caused by engine sensors and blown fuses. If your car is in limp mode the fault will be stored in the ECM.
You need to read the fault codes stored in your ECM to know which sensor has caused this problem. You didn't say what model vehicle you have and it would take a number of hours to list all the possible codes and reasons.
Get someone with a code reader for your model vehicle.

Limp Mode is usually a transmission failure
that will have to be diagnosed-check for codes
& google what they are

There are overheating & possibly other limp
modes on some vehicles

Can't use it at all like that & not cause a problem

Need a repair shop or dealer

Limp in mode has to deal with engine sensors and electrical power and grounds from the computer IF the basic engine is good such as compression, fuel pressure, charging system.

Use a bottle of yellow HEET dry gas to remove any moisture problem in the fuel.

Clean / replace air filter.
Check ATF at level ground. Top off ATF to MAX level.

You may have to have your ******/computer ran for any codes to give you a better idea of why it is limp mode. There are many causes of limp mode. A sensor or solenoid or bad wire will send the computer into limp mode. The TPS and map sensor both can affect limp mode

you need to know what caused the limp mode and repair it otherwise you won`t be able to get it out of limp mode.