This is for Medtronics Brand. Not sure how the others work.
Whenever you get a Cal Error, it will tell you to Meter BG. You will normally get two chances to get a good calibration. If, you get a second Cal Error you will get a Bad Sensor reading and you will need to insert another sensor. This is what I found to help avoid getting a bad sensor.
Turn off the sensor, do everything that is needed to get a good stable glucose reading. This may take some time. Restart the CCM. You can choose the new sensor or lost sensor button and it should start working again.
I should add that I also, look at the ISIG number to give me an idea if the sensor is ending. Another words, if it's low like around 5 that's usually a sign that it probably needs changing so, trying to restart it would be a waste of time.
The opinions expressed in WebMD User-generated content areas like communities, reviews, ratings, or blogs are solely those of the User, who may or may not have medical or scientific training. These opinions do not represent the opinions of WebMD. User-generated content areas are not reviewed by a WebMD physician or any member of the WebMD editorial staff for accuracy, balance, objectivity, or any other reason except for compliance with our Terms and Conditions. Some of these opinions may contain information about treatments or uses of drug products that have not been approved by the U.S. Food and Drug Administration. WebMD does not endorse any specific product, service, or treatment.
Do not consider WebMD User-generated content as medical advice. Never delay or disregard seeking professional medical advice from your doctor or other qualified healthcare provider because of something you have read on WebMD. You should always speak with your doctor before you start, stop, or change any prescribed part of your care plan or treatment. WebMD understands that reading individual, real-life experiences can be a helpful resource, but it is never a substitute for professional medical advice, diagnosis, or treatment from a qualified health care provider. If you think you may have a medical emergency, call your doctor or dial 911 immediately.