DEFINITION: A visible indication of an external fluid leak from the transfer case.

Review the Symptoms - Transfer Case and perform the necessary inspections.

Drain plug or fill plug leak

1. Inspect the drain or fill plug gasket for being faulty.
2. Install the plugs correctly. Refer to Transfer Case Fluid Replacement .

Hole plug leaking

Replace the access hole sealer.

Vehicle speed sensor leaking

1. Remove the vehicle speed sensor (VSS).
2. Inspect for the following conditions:

•	Cross threaded

•	Cut or damaged O-ring seal

•	VSS over tightened causing deformation in the VSS

•	Refer to Transfer Case Speed Sensor Replacement .

3. Replace the VSS O-ring seal if faulty. Refer to Transfer Case Speed Sensor Replacement .
4. Replace the VSS if faulty. Refer to Transfer Case Speed Sensor Replacement .

Rear output shaft seal leaking

1. Inspect for the following conditions:

•	Overfilled or improper transfer case fluid

•	Blocked vent

•	Seal improperly installed, worn or damaged

•	Seal bore damaged or cracked

•	Rear output shaft bushing for excessive wear

•	Slip yoke seal surface for wear or pitting

2. Repair or replace the following components if found faulty:

•	Adjust or replace the transfer case fluid. Refer to Transfer Case Fluid Replacement .

•	Clean or properly route the vent hose.

•	Replace the slip yoke if the surface could cause leakage. Refer to Front Propeller Shaft Replacement , One-Piece Propeller Shaft Replacement or Two-Piece Propeller Shaft Replacement in Propeller Shaft.

•	Replace the rear bushing if worn. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.

•	Replace the rear case half if the seal bore is damaged. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.

•	Replace the rear output shaft seal. Refer to Rear Output Shaft Seal Replacement .

Front output shaft area leak

1. Inspect for the following conditions:

•	Overfilled or improper transfer case fluid

•	Blocked vent

•	Loose yoke flange nut

•	Missing or damaged yoke flange O-ring seal

•	Yoke flange seal surface worn or damaged

•	Seal improperly installed, worn or damaged

•	Seal bore damaged or cracked

2. Repair or replace the following components if found faulty:

•	Adjust or replace the transfer case fluid. Refer to Transfer Case Fluid Replacement .

•	Clean or properly route the vent hose.

•	Replace the front case half if the seal bore is damaged. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.

•	Replace the yoke flange nut and O-ring seal if loose. Refer to Front Output Shaft Seal Replacement .

•	Replace the front output shaft seal. Refer to Front Output Shaft Seal Replacement .

•	Replace the front yoke flange if seal surface is faulty. Refer to Front Output Shaft Seal Replacement .

Control actuator shaft seal leaking

Replace the control actuator shaft seal. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.

Leaking at the vent tube

Leak at transfer case adapter weep hole - Automatic transmission only

1. Inspect for the following conditions:

•	Transmission fluid level low

•	Refer to Transmission Fluid Check in Automatic Transmission - 4L60-E/4L65-E and to Transfer Case Fluid Replacement .

•	Transmission rear seal for leaking

•	Transfer case input shaft seal for leaking

•	Cup plug in transfer case input shaft for leaking

2. Repair or replace the following components if found faulty:

•	Replace the transmission rear seal if leaking.

•	Refer to Propeller Shaft Front Slip Yoke Oil Seal Replacement in Automatic Transmission - 4L60-E/4L65-E.

•	Replace the transfer case input shaft seal.

•	Refer to Input Shaft Seal Replacement .

•	Inspect for the following conditions:

-	Seal improperly installed, worn or damaged

-	Seal bore damaged or cracked

-	Input shaft seal surface worn, grooved or damaged

•	Replace the cup plug in the input shaft if leaking. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.

Leak at transfer case mounting weep hole - Manual transmission only

1. Inspect for the following conditions:

•	Transmission fluid level low

•	Refer to Transmission Fluid Replacement in Manual Transmission - Aisin AR5 and to Transfer Case Fluid Replacement .

•	Transmission rear seal for leaking

•	Transfer case input shaft seal for leaking

•	Cup plug in transfer case input shaft for leaking

2. Repair or replace the following components if found faulty:

•	Replace the transmission rear seal if leaking.

•	Refer to Transmission Housing Oil Seal Replacement - Rear in Manual Transmission - Aisin AR5.

•	Replace the transfer case input shaft seal if leaking.

•	Refer to Input Shaft Seal Replacement .

•	Inspect for the following conditions:

-	Seal improperly installed, worn or damaged

-	Seal bore damaged or cracked

-	Input shaft seal surface worn, grooved or damaged

•	Replace the input shaft if the seal surface is worn. The rear output shaft seal, of the manual transmission, seals on the input shaft of the transfer case.

•	Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.

•	Replace the cup plug in the input shaft if leaking. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.

Case leaking

1. Inspect for a cracked case or case porosity.
2. Replace the faulty case half. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.

Front case half to rear case half seam leak

Disassemble and seal the case halves. Refer to Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.

Switch leaks

1. Remove the NEUTRAL or 2/4 indicator switch if leaking.
2. Inspect for a faulty gasket.
3. Replace the faulty switch gasket. Refer to Transfer Case Neutral Switch Replacement or Transfer Case 2/4 Indicator Switch Replacement .

Shift shaft detent plug leaking

1. Inspect the leaking plug for the following conditions:

•	Proper sealant

•	Stripped or damaged threads on the plug or the case.

•	Incorrectly tightened

2. Replace the detent plug if faulty and install correctly. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.

Shift shaft plugs leaking

Replace the leaking shift shaft plug. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - Isuzu T150 Unit Repair.