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  • karjunkie 12/18/09 6:44 pm PST

    The computer controlled NP-136 transfer case uses two speed sensors to sense the difference in speed between the front output shaft and the rear output shaft, and engages the front axle accordingly. These trucks use an "Active On Demand" transfer case. Basically its a normal 4x4 transfer case with a big electrically actuated (by way of a motor) clutch that connects the front prop-shaft (which is being spun by the wheels full time) to the transfer case front output. Its all in the transfer case. I'd check all the fuses and the wire harness to the encoder motor and replace the encoder motor if it has gone bad. It could also be one of the speed sensors is not working and not engaging the AWD. Did you have the PCM scanned for trouble codes? I have to agree with your instructor as 9 times out of 10 it is the encoder motor.

  • zolecki 12/20/09 7:33 am PST

    Thank you for the detailed response. He ran a diagnostic on it and he told me that what it was saying is that either the computer or the encoder motor was bad, that is all he told me. I will recheck the fuses and wires, but will also go ahead and get the motor. Thank you very much.

  • karjunkie 12/20/09 8:49 am PST

    Glad to try and help! Let me know if you got it working again, as we can pass the info on to others.

  • zolecki 12/22/09 3:49 pm PST

    When I was having problems there was a loud clicking sound coming from the awd computer when the vehicle was turned on. I put in a used shift motor and now there is no clicking but the awd still doesnt work. All the wires and fuses have been checked. Are there fuses under the hood for the awd and what else could be the problem? I will talk to the instructor tommorow, but I wanted your input as well.

  • karjunkie 12/22/09 4:12 pm PST

    All I can think of is those speed sensors are not activating the AWD. I would think you'd have some codes on that though. I'd start by cleaning the connectors on the speed sensors with some electrical contact spray and see if that helps.

  • zolecki 03/28/10 9:11 am PST

    I replaced the computer, the shift motor and a bad wheel speed sensor and nothing has worked.

  • curtis21 03/10/11 8:17 pm PST

    I just had my 2003 Olds Bravada checked out at my locale shop and the codes that came up were serveral but it said to replace transfer case encoder motor. Also check the fuse in fuse box my shop said my was missing.I hope this solves you problem.

  • 87silver 10/30/11 10:26 pm PST

    I also have a 2000 Bravada with 107k mi in which the check AWD light came on. I tried to put a scanner onto the port, but found no reading. There is a 10A fuse for the computer and a 20A fuse for the entire AWD system. If the 20A is blown, it will take the computer down with it. This was the case in mine. I replaced the encoder and the AWD was active again. But now the clutches in the transfer case were binding, so I flushed it and added the new spec fluid. I then drove it in a parking lot under 5mph turning the wheel lock to lock until it was freed up. Then changed the fluid again. The AWD system is now nice and responsive again.

    Source: I didn't read this somewhere; This is cold hard logic and experience.

  • roy08 11/15/12 11:17 am PST

    hi i have a 99 olds bravada with 168000 miles and the service awd light came on and stayed on when i turn over the truck and i put in a used encoder motor in and the light went away when started the truck but a few hundred feet down the road the light comes on untill i shut off the truck and turn it back on the light goes away and when i start the truck and start going the truck is in awd but when the light comes on the awd disengages. can someone please help me here. i look for everthing that can cause this and no help. thank you

  • skinny10 12/14/14 12:43 pm PST

    Did some research... as others have stated, the replacement of the Encoder Motor which I purchased from Rock Auto did the trick. fairly easy repair, hardest part other than making sure that the vehicle is securely stationed on jack stands(only front wheels)... was to get the old electrical connector apart and new one back on , have to get both hands above the transfer case to do it. My AWD did not work at all before this replacement, works perfectly after. I also disconnected the battery for awhile, and checked all of the fuses that could have any effect on this .I understand that this may not be the solution every time, but it was easy and only cost 129.00 shipped. Best of luck everyone.

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