If your vehicle is showing seatbelt height adjuster on the pillar is jammed or won't lock in place, here are the most likely causes and the parts you'll need to fix each one.
Over time, dust, dirt, and interior grime can accumulate inside the B-pillar track, causing the sliding mechanism to bind, stick, or become difficult to move.
The internal spring or plastic locking tab that holds the adjuster at the desired height can wear out or snap from repeated use, causing the adjuster to slide freely without locking.
If the B-pillar trim was recently removed for interior work, the seatbelt anchor bolt may have been over-tightened or the plastic trim misaligned, physically pinching the sliding mechanism.
Excessive force, such as yanking the belt violently or a previous collision, can bend the metal track inside the pillar, making it impossible for the adjuster to slide or lock properly.