[klinn]

Originally Posted by skipr

File In Section: 04 - Driveline Axle

Bulletin No.: 99-04-21-002

Date: April, 2001

TECHNICAL

Subject:
Four-Wheel Drive (4WD) Inoperative
(Replace Transfer Case Actuator/Shift Detent Plunger)

Models:
1999 Cadillac Escalade
1998-01 Chevrolet and GMC C/K Models (Tahoe, Denali, and Yukon)
with 4L60-E or 4L80-E Automatic Transmissions (RPOs M30, MT1)
and NV246 Transfer Case (RPO NP8)

Condition

Some owners may comment that the 4WD is inoperative.

Cause

This condition may be caused by an inoperative transfer case motor (actuator).

Correction

A new transfer case 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 transfer case actuator is inoperative, replace the actuator and the poppet. Use the following procedure and the part numbers listed below.

1. Remove the transfer case actuator.

2. Install a new transfer case actuator, P/N 12474401.

3. Remove the transfer case oil drain plug. Drain the oil from the transfer case. Refer to the Transfer Case subsection in the appropriate Service Manual. If the plug is difficult to remove or stripped, refer to Corporate Bulletin Number 99-04-21-001.

4. Remove the plunger (poppet) screw. The poppet and the spring should come out with the screw.

Notice o not overtighten the poppet screw.

Overtightening may damage the screw.

Important : Verify that the 0-ring on the screw is not damaged. Replace a damaged 0-ring.

5. Install the new coated poppet, P/N 12474072 (coated blue), the spring, and the screw.

Tighten

Just so you are aware, that bulletin is for the older square front end silverado trucks (refered to as the GMT400 body line). In midyear 99 the rounded front end trucks came out (these are refered to as the GMT800 body line). The 2000 Z71 should be the GMT800 truck and that bulletin would not apply. I did find a bulletin for the transfer case module, but there are specific diagnostic trouble codes for the bulletin to apply. You need to have the transfer case module scanned for codes. If you can, post the DTCs when you get them, and I might be able to help further. The bulletin I found if for DTC B2725, and it states you should also have a "service 4wd" light on also. The ultimate fix for that is to replace the push button switch (transfer case shift control switch), but again only if the truck is acting exactly as the bulletin describes. It is really important to have the truck scanned for codes. Hope this helps.