I have a 99 jimmy 4wd with the 4wd high, 4wd low, and auto 4wd settings. My 4wd low will engage if I give it a good amount of time but the other two won't come on no matter what I do (neutral, drive, drive going 2-4mph). Anyone else have this problem? Any guesses?

 

Check out the DIY section for finding out what codes are stored in the TCCM (located under dash). If the TCCM stores codes then it can stop the 4x4 switches from working. Do the lights function normaly when you turn on the keys? This is the time when the computer checks electrical connections and circuits for malfunctions, if there are any problems during this time it will be stored in the TCCM for 4x4 functions. You have to get the codes scanned to find out what the problem is. With this electronic 4x4 it will go into default mode ie 4lo only from 2hi and back if there are problems in the system then it will not let it work fully to keep from breaking parts...

 

If it has Auto4wd, then the DIY article will not help. You will either need a Tech2 or equivalent scanner to access the TCCM via the DLC (data link connector). The TCCM on the Auto4wd is a serial link to the PCM not the old ALDL which could be accessed via the procedure in the DIY section.

I would suggest that you remove the TCCM (passenger side kick panel) and clean the connections. Also remove the electrical connection from the encoder motor on the transfer case and clean that connection as well. Use some electrical contact cleaner to clean out the terminals and then apply a thin coating of dielectric grease to the female plug and reassemble.

If that doesn't work, then you really should have it scanned. It will cost a bit of money ($70 around me if I had to go to the dealership), but it should identify the malfunctioning part.