My AEM X-Series OBDII gauge keeps rebooting showing "OBD2" and does not display data. What's wrong?

The AEM OBDII gauge only works with the CAN bus protocol of the OBDII port. An OBDII port can use any of five communication protocols, and many cars (especially older models, e.g. a 2007 Fiat Panda) use a non-CAN protocol. A generic phone OBD adapter supports all protocols, which is why it may work when the AEM gauge does not. First test the gauge on another car that uses CAN to confirm the gauge is working. If your vehicle does not use CAN on OBDII, this gauge cannot read it.