[TheOtherOne]

It seems this may be the encoder motor in the transfer case.

I got the following information from another message board. Does anyone know if it applies to a 1999 Tahoe?

It is very important that the mounting surfaces be clean and free of debris. The sealing

O-ring must be correctly in place on the encoder pilot to ensure a positive seal

SERVICE PROCEDURE (for 1992 S-10 Blazer 4.3W pushbutton 4WD)

To remove the encoder motor assembly:

1. Disconnect the negative battery cable.

2. Raise the vehicle and support with suitable safety stands.

3. Disconnect the electrical connection to the transfer case encoder.

4. Remove the front propeller shaft.

5. Remove the front output shaft yoke

6. Remove the encoder motor assembly by removing the (3) 8mm hex bolts.

NOTE: REMOVE ONLY THE 8mm HEX NUTS AS SEVERE DAMAGE TO INTERNAL COMPONENTS OF THE encoder

MOTOR ASSEMBLY MAY RESULT IF THE TORX HEAD BOLTS ARE REMOVED. DO NOT REMOVE THE TORX HEAD

BOLTS.

To install the encoder motor assembly:

1. All mounting surfaces must be clean and free from burrs and debris.

2. Set the sealing 0-ring on the encoder motor pilot.

Note: Check the alignment of the transfer case sector shaft with the drive sleeve in the

encoder motor assembly. The transfer case should be in 4-High (The flats on the sector shaft

vertical) for proper alignment. Rotate the transfer case sector shaft for proper alignment if

required.

3. Install the encoder motor assembly. Torque the bolts to 18 N.m (13 lbs.ft.).

4. Install the front output shaft yoke as outlined in section 7D-13 of the 1992 or 1993 S-10

Truck Service Manual (TRANSFER CASE OUTPUT SHAFT SEAL REPLACEMENT).

5. Install the front propeller shaft.

6. Connect the encoder motor electrical connection.

7. Connect the negative battery cable. Lower the vehicle.