Transfer Case Will Not Shift

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2011 GMC Yukon XL, 2011 GMC Yukon, 2011 Chevrolet Tahoe, 2011 Chevrolet Suburban, and 2011 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Cause	Correction
DEFINITION: The transfer case will not shift from 2 wheel drive to 4 wheel drive or there is a gear clashing when shifting from hi to lo modes. When shifting from 2HI or 4HI to 4LO, the transmission must be in neutral and the vehicle speed below 3 mph. Review the correct owners manual shifting procedures with the customer. Inspect for the correct fluid level. Inspect the drain plug for large metal deposits. Small metal flakes and fine metal dust on the plug magnet are to be considered normal. Review the Symptoms - Transfer Case and perform the necessary inspections.
Front axle actuator	NOTE: A transfer case that will not shift into 4WD may be caused by the front axle actuator. If the symptoms occur during cold temperatures, flush and fill the front axle with synthetic fluid. Refer to Front Axle Lubricant Level Inspection (9.25 Inch Axle) , Front Axle Lubricant Level Inspection (8.25 Inch Axle) . Perform the Diagnostic System Check - Vehicle (with HP2) , Diagnostic System Check - Vehicle (without HP2) before using the symptom tables, in order to verify the following conditions are true: There are no diagnostic trouble codes (DTCs) present. The control modules can communicate via the serial data link. Inspect for an intermittent. Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections . Some symptoms may be caused by loose wiring. Test the system after moving or connecting harnesses, but before replacing parts. Refer to Four-Wheel Drive Does Not Engage .
Electrical system	Perform the Diagnostic System Check - Vehicle (with HP2) , Diagnostic System Check - Vehicle (without HP2) before using the symptom tables, in order to verify the following conditions are true: There are no diagnostic trouble codes (DTCs) present. The control modules can communicate via the serial data link. Inspect for an intermittent. Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections . Some symptoms may be caused by loose wiring. Test the system after moving or connecting harnesses, but before replacing parts. Refer to Four-Wheel Drive Does Not Engage .
Transfer case shift fork pads broken or missing	NOTE: A growl, rattle, or grinding noise that occurs when a shift is commanded may be caused by broken or missing shift fork pads which may lead to incomplete engagement of the high/low clutch teeth. Refer to High/Low Shift Components Cleaning and Inspection . Replace the shaft forks and pads as required. Refer to Transfer Case Disassemble , and Transfer Case Assemble .
Transfer case high/low clutch gear tooth damage	NOTE: Excessive gear tooth damage may cause a will not shift or gear clash when shifting condition. Inspect the gear teeth for excessive damage. Refer to High/Low Shift Components Cleaning and Inspection . Inspect the splines of the high/low clutch and rear output shaft to ensure the clutch moves freely on the shaft. Replace components as required.
Clutch pack	A worn clutch pack may set a DTC and disable shifting. Refer to Diagnostic System Check - Vehicle (with HP2) , Diagnostic System Check - Vehicle (without HP2) .
Shift levers and shift components	NOTE: An incorrect technician repair using mismatched heavy duty (HD) and light duty (LD) shift levers and shift lever balls may lead to a will not shift condition. Refer to Transfer Case Description and Operation for additional shift lever and shift lever ball information. Apply plate installed incorrectly after a service overhaul. Worn shift lever components may set a DTC and disable shifting. Refer to Diagnostic System Check - Vehicle (with HP2) , Diagnostic System Check - Vehicle (without HP2) .
Rear output shaft snap ring broken or out of position	NOTE: A broken or mis-positioned rear output shaft snap ring may lead to a will not shift condition. Inspect for a broken or mis-positioned rear output shaft snap ring.
Transfer case high/low planetary carrier assembly	NOTE: In situations where there is excessive input shaft gear teeth wear, it may not be possible to engage 4LO. Inspect the planetary gears and high/low internal gear for wear or damage. Refer to High/Low Planetary Carrier Cleaning and Inspection . Inspect the input shaft gear teeth for wear or damage Replace components as required.