This sounds like you have a speed sensor issue. Typically if the motor turns and the speed sensor is dirty, the wire is loose, or the sensor is not close enough to read the flywheel correctly, the treadmill does stop with an error code. If you have an idea where the speed sensor is, you may want to do the following. Get canned air and blow away any debris, spider webs, or dust away from the speed sensor. You can also disconnect it from the main power board and reconnect it. It may be loose. Last, if there is an adjustment bracket (something that can be loosened then tightened to move the sensor closer to the flywheel), then you should move it closer to the flywheel It needs to
be a credit card's distance from the flywheel, but not touching. Worst case scenario, you have a bad sensor. In that case, you will need a new speed sensor.