Includes Keys, Ironman, Alliance, Milestone, Encore, Health Trainer, some Smooth models, some Cardio Zone models, Galyans, and several other brands.
Meaning of code:
The safety key is missing. The key is not hitting the switch properly. You may need to remove the console and make sure the key is hitting the switch (if you have an insertable key). If you have a magnetic switch, the safety switch pickup on the underside of the console may have moved. These can be easily hot glued back in place.
Turn off the treadmill, unplug it, wait 30 seconds, then plug it back in and put the safety key in place. Make sure the metal piece below the "emergency stop" sticker is still in place.
Try the calibration help topic from our repair help section.
If all the switches check out and the treadmill still won't clear the SI1 code, you need to replace the console.