The 2000 GMC Jimmy was one of the first generation of GMC Vehicles where four-wheel drive could be engaged through dash-mounted buttons that tied into mode switches and electronic controls rather than the old school, floor-mounted switch. Like older model four-wheel drives, the SUV needed to be idle when gears were shifted from two-wheel to four-wheel drive and it was recommended that four-wheel drive not be engaged while on dry pavement. The system changed somewhat in the early 2000s as GMC redesigned its line of trucks and SUVs.
GM 4WD warning lights normally come on briefly for several seconds when the vehicle is turned on and when moving between 2WD and 4WD. However, they are not lights that signal a time for routine maintenance. If they come on while driving or come on and then began blinking, it can signal a number of potentially serious conditions that need attention.
The light should shine for several seconds when shifting from 2WD to 4WD. If the light only blinks briefly, it is signaling the vehicle did not succeed in shifting gears. This could signal a faulty position sensor in the encoder motor.
Blinking will occur if you are attempting to shift in a manner that is not allowed, such as trying to shift into 4WD when the vehicle is in motion. To successfully shift gears, the Jimmy must be either stopped or in neutral. .
Software failures are rather common problems as these vehicles ages. The warning light will appear when the transfer case control module (TCCM) software is failing. This will require replacing the TCCM
The actuator in the front differential may be sticking and need to be replaced. Check all vacuum hoses for leaks. Also check the actuator itself to see it the cable is pulling the axle coupler.
