1998 Tahoe 4WD problem

first snow and icy conditions today so I wanted to try the 4 wheel drive out for the first time since I bought my Tahoe. It has the push buttons on the dash 2 wheel Hi, 4 wheel Auto, 4 wheel Hi and 4 wheel Low. I read the owners manual and it says to push the appropriate button and the light on the button will flash until it engages and then the light will glow steady. Mine flashes and never glows steady and it remains in 2 WD. What are the reasons it would do this?

is there any service 4wd light on the i/p cluster? do you actually hear the t-case shift?

thanks for your reply. There is no light on that indicates trouble and I haven't notice a sound that I would associate with a shift to four wheel drive. The truck only has 91000 and has been well cared for. I just expected the 4WD to function properly. When I drove it in bad conditions yesterday I just thought it was in 4WD, but apparently it gets around pretty good in rear wheel drive only..lol. It took me a little while to realized that it hadn't shifted to 4WD . I am not familiar with this vehicle and don't know how it feels when it's 4WD is activated. I have a 4WD Ford Ranger and there is a big difference in it's feel between 2 and 4 WD so I expected that same assurance that the Tahoe was in 4WD. I had to read the manual to know that the light on the switch should not be blinking. I first tried the auto high and it blinked for awhile and then went back to 2 WD high. The 2 WD light is on steady as it should be. I currently have a truck in the transmission shop because reverse went out so I suppose I'll ask him what he thinks is wrong with the Tahoe when I pick up my other truck. I was hoping it would be something simple or common to these vehicles and I could get a clue as to what it might be and what needs to be done to fix the problem.

put it in neutral and press 4lo. you should definitely hear and feel a clunk even if the front axle does not engage. that would be the t-case shifting first. if it does not shift check fuse TCASE #2 20amps and 4WD #24 20amps. both located on the i/p fuse block. if it still does not clunk as it should either the tccm relay is bad(it should click when attempting to shift and you can hear it under the left dash) or the shift motor or its circuit is bad.

SunlitComet said:

put it in neutral and press 4lo. you should definitely hear and feel a clunk even if the front axle does not engage. that would be the t-case shifting first. if it does not shift check fuse TCASE #2 20amps and 4WD #24 20amps. both located on the i/p fuse block. if it still does not clunk as it should either the tccm relay is bad(it should click when attempting to shift and you can hear it under the left dash) or the shift motor or its circuit is bad.

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I checked the fuses and they appeared good, but I swapped them with other fuses that I knew were working and still no clunk and yes there is a click under the dash left side. It clicks when I choose 4WD and when I go back to 2WD. Does that mean my tccm is good?

the tccm is functioning but whether the relay in it or the shift motor works is another story. use the document below to test for continuity of the shift motor and brake while it is disconnected from the system and test the outputs of the tccm to the shift motor to see if the shift motor is receiving power as it should when attempting a shift. the brake is energized while the shift motor changes settings.

SunlitComet said:

the tccm is functioning but whether the relay in it or the shift motor works is another story. use the document below to test for continuity of the shift motor and brake while it is disconnected from the system and test the outputs of the tccm to the shift motor to see if the shift motor is receiving power as it should when attempting a shift. the brake is energized while the shift motor changes settings.

Click to expand...

Thanks for your help.

SunlitComet said:

the tccm is functioning but whether the relay in it or the shift motor works is another story. use the document below to test for continuity of the shift motor and brake while it is disconnected from the system and test the outputs of the tccm to the shift motor to see if the shift motor is receiving power as it should when attempting a shift. the brake is energized while the shift motor changes settings.

Click to expand...

I took it to the transmission shop that just did a rebuild for my Ford Ranger. They did a scan and determined that it was the actuator. his cost from O'Reilly's was $76.00 and they installed it while I waited and it fixed the problem. Since I had just spent a *** on my other vehicle he did it for cost of parts + tax and no labor so 82.00 bucks took care of it. I'm glad to have it working properly for the upcoming winter. Thanks again for your help. I wanted to let you know what the problem turned out to be and the fix.

your service 4wd light does work tho correct?

Thanks! I had just run into the same issue with my 99. It turned out to be the TCASE #2 fuse. I replaced it and it's working fine now. I've always subscribed to the "fuses don't blow for no reason" theory. What would cause that fuse to blow and is it a sign of something big to come on the repair front? I also conveniently subscribe to the "sometimes fuses just blow" theory. I really am my own worst enemy!