99 Tahoe front axle won't unlock

[chris peter]

I replace my transfer case (NP8) motor because it would not shift in to neutral. Did not want to have any problems this winter. Now it won't shift into 2WD or neutral and when in 4WD Auto the front axle is locked all the time. I did not want to try 4WD LO because if it got stuck that would be worse. I can hear the motor working and the light blinks but goes back to 4WD. I was in 2WD when I started the project and had not tried the 4WD for sometime. When driving no strange noises but it is locked in 4WD you can tell when you make a turn. When I installed the motor I had to shift the transfer case with a crest wrech but it clicked in some what easy but i'm not sure how easy it should be I thought it was a little hard to move. That was done to line up the motor with the transfer case. I can hear the front axle actuator making noise when you shift from 4WD to 4WD Auto but no noise from 4Wd to 2WD. Did I get a bad motor or is it the front Axle actuator not unlocking you would think in 4WD auto it would unlock. I disconnected the battery and also tried pulling #2 fuse in both cases you can hear the motors but same result. I change the transfer case fluid every spring always looks good. Could a bad axle actuator be the problem if it is stuck engaged. Any Ideas would be helpful please.

[chris peter]

Update, just went and checked wiring connections and found that the body control module has been replaced. I purchased truck used so the previous owner replace it with a used part. Would that need to be reprogramed or on a 99 tahoe with NP8 is not programable on that model year.

[chris peter]

Update Replace the transfere case motor for the second time with a new motor that came in the neutral position and now I'm stuck in neutral position. I have no blown fuses. I did have power to the motor. I can hear the tccm clicking four or five times when I turn the Ignition on but when I push any of the buttons they don't even light up. The tccm clicked two times before now it clicks a lot more. Anyone Ideas please.

[j cAT]

your post is a little hard to follow exactly.

the vehicle in auto 4wd is when the front axles are locked as one.the front diff actuator does this.

when in 4wd low/hi the encoder motor engages the front locked axle to the rear axle.

lets say you cannot get the vehicle to go from 4wd to 2wd . then you must examine the fluid condition. is it blue ? if not then the transfercase is n/g.

the bcm normally needs to be programmed. but you have had this vehicle for some time so if it worked before it should be ok.

with no service 4wd lights and the drivetrain not responding correctly this is usually the transfercase ..

the 4wd select switch will cause the service 4wd light to come on but just to be sure change it or resolder the pins on the switch circuit board...

[chris peter]

j cat thanks for your response. I have more information for you the 4wd service light is on. when I turn the key on the tccm clicks 4-5 times it never did this before. The red neutral light is on when I push 2wd, 4wd, Auto, 4low the lights now don't even light up. The new motor I put on does not make any sound at all. No blown fuses. I had it scanned at the dealer and the result was an open circuit in the encoder motor. Thats why I installed this second motor. Before when I was stuck in 4wd high( first motor I installed) the front axle was locked in even in 4wd auto the hub would not unlock. Do you think I have a bad tccm? The fluid was changed 2 months ago it was blue and the 4wd selector switch is new. When I installed the motor I had to put the transfer case into neutral to install the motor and I did not think it was to hard to shift the sector into neutral it took a little effort but not to much.

[j cAT]

Originally Posted by chris peter

j cat thanks for your response. I have more information for you the 4wd service light is on. when I turn the key on the tccm clicks 4-5 times it never did this before. The red neutral light is on when I push 2wd, 4wd, Auto, 4low the lights now don't even light up. The new motor I put on does not make any sound at all. No blown fuses. I had it scanned at the dealer and the result was an open circuit in the encoder motor. Thats why I installed this second motor. Before when I was stuck in 4wd high( first motor I installed) the front axle was locked in even in 4wd auto the hub would not unlock. Do you think I have a bad tccm? The fluid was changed 2 months ago it was blue and the 4wd selector switch is new. When I installed the motor I had to put the transfer case into neutral to install the motor and I did not think it was to hard to shift the sector into neutral it took a little effort but not to much.

if you can get the dtc code number for that 4wd failure . the locking of the front axle is the locking actuator motor in the front axle.

the open circuit may mean wiring issues. you will need to follow back the wires , not easy job. check the 4wd control module behind the 4wd switch assy. check for connector/wire failures..

[chris peter]

j cat when I install the new motor I disconnected the battery. So after I connected the battery thats when it new it was in neutral. The hubs must have unlocked. I realize I should get it scanned again but now I'm stuck in neutral. I'm tempted to pull the endcoder motor disconnect the front actuator wire and manually put it in 2wd so I can get it to the dealer. I did find this (A new transfercase Teflon(R)-coated shift detent plunger (poppet) has been developed in order to correct this condition. This coating on the exterior surface of the poppet should reduce shift effort and wear. If you determine that the transfercase actuator is inoperative, replace the actuator and the poppet. What do you think could this be my fix? Where is this (poppet) located? This is a service bulletin. Have you heard of this?

[chris peter]

Problem solved, Here's the solution I purchased the truck from someone that never used the 4wd. The transfer case shift sector was very tight from no use. I installed a new transfercase Teflon(R)-coated shift detent plunger (poppet) GM Part #12474072 and fresh auto trac II fluid. Then put a cresent wrench on the shift sector coming out of the transfer case and worked it at least a 100 times until it felt like shifting my motorcycle trans nice easy clicks. It was so tight before it was causing the encoder motors to fail right away. I had the transfer case scanned at the dealer twice and it said bad encoder motor open circuit both times 2 new motors turned into junk. The parts store was good about taking the motors back. Now I think every fall I will remove the encoder motor work the shift sector with fresh auto trac fluid in the transfer case before winter.