* Binding in the Front Differential: This is the most likely culprit. With 4WD and the inter-axle lock engaged, all four wheels are mechanically linked. If there's a problem within the front differential (broken or severely worn components, debris, etc.), it could bind, causing one or more wheels to lock.
* Binding in the Front Axle: A problem with the CV joints, axles, or wheel bearings on the left side could also cause binding, leading to the locked wheel. This could be exacerbated by the 4WD engagement.
* Inter-axle Lock Issue: While less likely to cause a *single* wheel to lock, a malfunctioning inter-axle lock could contribute to the problem. It's possible the system is binding or applying excessive force unevenly.
* Brake Caliper Seizure (Less Likely): A severely seized brake caliper on the left front wheel could contribute to the issue, but it would likely be noticeable even in 2WD. The fact it's locked while parked in 4WD with the inter-axle lock engaged suggests a drivetrain problem is more prominent.
* Transfer Case Problem: Though less common, a problem in the transfer case could contribute to the binding if it's improperly engaging or disengaging.
Crucially: Do not attempt to force the wheel to turn. You risk causing significant damage to the drivetrain.
What to do:
1. Do not drive the vehicle. Towing it is necessary.
2. Have it professionally diagnosed: A qualified mechanic specializing in 4WD systems needs to inspect the vehicle. They'll likely need to check the front differential, axles, and transfer case. They can determine the exact cause of the binding.
3. Do not attempt DIY repairs unless you have extensive experience with 4WD systems. Incorrect repairs can cause further, more costly damage.
The combination of 4WD engagement, the inter-axle lock, and a single wheel locking strongly indicates a mechanical issue within the drivetrain that requires professional attention.
