Code E1: Solution 1: Under the hood of the treadmill, near the cylinder over which the belt runs, is a readout sensor that measures speed. If the reading sensor is too far away from the magnet, the speed cannot be read and the display shows code E1. Slide the reading sensor a little more toward the magnet until it just passes it. Solution 2: If solution 1 does not help, the cable connected to the reading sensor may have become loose due to vibration. Attach the cable to the reading sensor and to the circuit board.
Code E3: Code E03 means that there is a fault in the circuit board. This can be solved by replacing the entire circuit board. The circuit board is often attached with 2 screws, loosen them. Before pulling all the cables from the old circuit board, take a picture of the circuit board to see for yourself which cable is where. The cables are often attached with a little glue. This glue is hard and can be easily removed with a small screwdriver. Now that you have taken the picture you can insert the new circuit board and put the cables in the right place.
Code E7: The supplied "Safety Key" is not on the treadmill. Attach it to the display to get the treadmill running again.