98 Z71 4WD Problem

First off, I have studied http://www.automotiveforums.com/t692443-wont_go_into_4lo_or_hi_just_blinks.html and it appears our problem is something different.

My son's K1500 5.7 4wd will not engage, My son-in-law also has a 98 Z71 so we have a good truck to check parts and operations with.

We have swapped out the front differential actuator, the dash board switch, and have a brand-new transfer case actuator installed, but it still blows the transfer case fuse.

If we pull the 2-wire connector off the transfer case actuator and check it with a meter while pushing one of the 4wd switches the voltage fluctuates and you can hear the switch pulsating, s-i-l truck holds a stready 12v. The fuse will blow also if we unplug the 6-wire plug that I assume is connected to the front differential actuator.

What's the next step? Jump the wires from the t-case to the firewall and see if there is a short somewhere in between in the original harness? Does anyone have a recommendation for a good wiring diagram we could consult?

First off, I have studied http://www.automotiveforums.com/t692443-wont_go_into_4lo_or_hi_just_blinks.html and it appears our problem is something different.

My son's K1500 5.7 4wd will not engage, My son-in-law also has a 98 Z71 so we have a good truck to check parts and operations with.

We have swapped out the front differential actuator, the dash board switch, and have a brand-new transfer case actuator installed, but it still blows the transfer case fuse.

If we pull the 2-wire connector off the transfer case actuator and check it with a meter while pushing one of the 4wd switches the voltage fluctuates and you can hear the switch pulsating, s-i-l truck holds a stready 12v. The fuse will blow also if we unplug the 6-wire plug that I assume is connected to the front differential actuator.

What's the next step? Jump the wires from the t-case to the firewall and see if there is a short somewhere in between in the original harness? Does anyone have a recommendation for a good wiring diagram we could consult?


the vehicle does not go into 4wd...this means that the transfer case or encoder transfercase motor is defective....

the locking actuator is for the front diff and ONLY locks the front axles together,,,,it does NOT engage 4WD,,,,,


what fuse exactly blows,,,,and this fuse blows if I understand this correctly only when the transfercase encoder motor is connected?????

the vehicle does not go into 4wd...this means that the transfer case or encoder transfercase motor is defective....
So you are ruling out a wiring problem?

the locking actuator is for the front diff and ONLY locks the front axles together,,,,it does NOT engage 4WD,,,,,
Yes we know that, but does the 6 pin plug power the front diff actuator? And also power the 2H/4H/4L indicator lights?

what fuse exactly blows,,,,and this fuse blows if I understand this correctly only when the transfercase encoder motor is connected????? Fuse #2, TCase. When the 2-wire lead is disconnected from the new actuator it will not blow

Should we remove the Tcase actuator and plug the wires up to see if it will work properly? Should we try to manually rotate the transfer case shaft while the actuator is removed to see if the transfer case is defective?

The T-CASE fuse is "HOT AT ALL TIMES", so if it's blowing when you select 4WD then it could be an internal short in the T-CASE Control Module. If it's blowing as soon as you put a new one in then it's most likely a wiring problem.

So you are ruling out a wiring problem?


Yes we know that, but does the 6 pin plug power the front diff actuator? And also power the 2H/4H/4L indicator lights?

Fuse #2, TCase. When the 2-wire lead is disconnected from the new actuator it will not blow

Should we remove the Tcase actuator and plug the wires up to see if it will work properly? Should we try to manually rotate the transfer case shaft while the actuator is removed to see if the transfer case is defective?

I would remove the encoder motor from the vehicle and see if the fuse will not blow...if the encoder is binding this would increase the current so that the fuse will blow..

if the wire/connector is shorted to ground somewhere it would always blow the fuse,,,connected or not..to the transfercase ENCODER motor...

the voltage to this encoder motor reverses to engage or dis-engage 4WD...so if one wire going to it where shorted,,I guess it is possible with the voltage reversing it is possible one wire is shorted,to the ground/frame,which should be revealed when testing ..encoder removed..It sure appears that the encoder is binding.....

the front diff should not be of concern,,,your problem is no 4wd..
only the transfercase can do this..

what is the fluid condition???open drain plug and allow some of the fluid to come out for review..

Thanks to all, we will check these suggestions out.

We tried 2 aftermarket encoder motors with no luck. Gave up and took to tranny shop. He puts a GM encoder unit on and it work fine. And over $700 bill. After the bill he says the aftermarket encoders are no good. Luckily, O'Reilly's refunded the cost of the two encoders.

Now the 4wd quit again. Encoder and actuator all sounding like they are working right. With motor off, put in 4wd. Front driveshaft will not rotate by hand like it will in 2wd. Sounds right. Jack up front wheels and they are free wheeling in 4wd when we turn by hand and driveshaft doen not rotate.

Any more hints?

We tried 2 aftermarket encoder motors with no luck. Gave up and took to tranny shop. He puts a GM encoder unit on and it work fine. And over $700 bill. After the bill he says the aftermarket encoders are no good. Luckily, O'Reilly's refunded the cost of the two encoders.

Now the 4wd quit again. Encoder and actuator all sounding like they are working right. With motor off, put in 4wd. Front driveshaft will not rotate by hand like it will in 2wd. Sounds right. Jack up front wheels and they are free wheeling in 4wd when we turn by hand and driveshaft doen not rotate.

Any more hints?

what was the condition of the transfercase fluid ? what was the color of the transfercase fluid...drain plug debris ?before fix and after fix...

We tried 2 aftermarket encoder motors with no luck. Gave up and took to tranny shop. He puts a GM encoder unit on and it work fine. And over $700 bill. After the bill he says the aftermarket encoders are no good. Luckily, O'Reilly's refunded the cost of the two encoders.

Now the 4wd quit again. Encoder and actuator all sounding like they are working right. With motor off, put in 4wd. Front driveshaft will not rotate by hand like it will in 2wd. Sounds right. Jack up front wheels and they are free wheeling in 4wd when we turn by hand and driveshaft doen not rotate.

Any more hints?

Try turning a front wheel while in 4hi with only 1 wheel off the ground

after a closer look we see the right CV joint has gone to lunch...

after a closer look we see the right CV joint has gone to lunch...



what was the condition of the transfercase fluid ? what was the color of the transfercase fluid...drain plug debris ?before fix and after fix...