This error message almost always indicates an upper PCA problem when they are consistently displayed. Failures causing this error message to be displayed are rare.
If the error message is consistently displayed when the unit is powered up, the upper PCA should be replaced. It is possible to see this message displayed intermittently due to external causes. If the unit's AC input significantly dips during the power-up test sequence the test could fail resulting in this message being displayed. Treadmills operating on non-dedicated AC circuits may see this message displayed on an intermittent basis.