# How to debug a not connected sensor

The Built-In Self Test (BIST) will fail indicating that no sensor is connected with the BIST = 0x4F (79). This could be due to:

### Sensor connection

There's no sensor connected to the transmitter or the sensor is not properly connected. Ensure that the probe is in place and that the O-ring is tightly adjusted.

### Malfunctioning sensor

If the sensor is connected properly, another cause for the reported issue could be that the sensor being used is malfunctioning. To verify this follow the next steps:

1. Ensure there are no visible damages in the probe or cable of the sensor. 
2. If available, try a different probe that is working properly. To do this follow the steps on [how to replace the sensor or probe](https://docs.twtg.io/docs/how-to/vibration-sensor-vb/how-to-replace-the-sensor-or-probe). If the NEON Vibration Sensor works with the new probe, then it's extremely likely that the old probe is damaged/malfunctioning. Contact TWTG through the [service desk](https://www.twtg.io/servicedesk) to arrange a replacement if the device is under warranty.

### No connection between the transmitter's PCB and the sensor's PCB

In very unlikely scenarios the cable between the transmitter's PCB and the sensor's PCB can be disconnected. If this is the case, contact TWTG through the [service desk](https://www.twtg.io/servicedesk) to arrange the device's repair.


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