Getting an E2 Cal error but its only triggered when the weight is over 165 lbs. What could this be?

It seems like the issue might be related to lubrication or belt tension. When there's a larger load on the treadmill, it requires more effort to maintain speed. The E2 error indicates a speed issue, which aligns with the situation you're describing. Applying treadmill lubricant may help resolve the problem. We recommend using a treadmill-specific lubricant for the best results.