What is the most likely cause of occasional hard steering that becomes more common in the rain?

The observation of occasional hard steering that worsens in the rain points toward a problem that could cause variations in steering assist, particularly under different load conditions such as increased friction from wet roads. A loose power steering pump belt is likely to cause the power steering pump to operate intermittently or at a reduced output, especially if the pump struggles under heavy steering loads, which can be more pronounced in slippery conditions.

When the belt is loose, it may not fully engage the pump, particularly when extra effort is needed during turns or when navigating wet surfaces. This can lead to periods of inadequate steering assist, which might not be noticeable in dry conditions but becomes problematic when moisture increases the friction that the tires experience. Therefore, a loose power steering pump belt can directly lead to inconsistent steering ease, particularly when external conditions such as rain require smoother handling.

In contrast, other options may not specifically result in the behavior observed in this scenario. Low fluid level, for example, typically manifests as a constant lack of assist rather than intermittent issues, while a faulty power steering pressure switch might cause a different set of symptoms. Low tire pressure usually affects vehicle handling in a more general sense rather than causing the specific issue of hard steering predominantly when wet.