Service tire monitor light is on

First try the TPMS reset procedure. 1. key on engine off, parking brake on. 2. turn park lights on and off 4 times you will hear a horn chirp twice, you are in program mode. Start at L/F tire release air for 10 seconds, wait 15 seconds until horn chirp, after chirp go to R/F tire do the same until horn chirp then R/R let air out til the chirp then L/R do the same after the L/R chirp, turn key off and you are done, note you have only 5 min. to complete. If you do not hear horn chirp at each tire, you will have to start from beginning. When complete, remember to add air to each tire, 35 psi is recommended. If this does not work, you probably have a bad TPMS tire sensor which will require replacement. Some auto parts stores will diagnose your tire sensors for free, so check around.

Is it just a dummy light on the dash or is it more specific like L.F tire low,ect? if its a dummy light then you need to go to a garage with a tire pressure monitor service to to check to see if the batteries in the monitors are still good or if you are just dealing with a leaking tire. If you Tahoe uses wheel speed sensors to monitor tires and pressure you may have a faulty wheel speed sensor or a heads up that your wheel bearing is wearing and the gap between the tone ring and sensor have increase or decreased good luck