I just purchased a 2016 CX-5 touring in Titanium Flash Mica color. There were a few error codes that I could not find an explanation for. I ended up buying the car anyway because it was in good condition and the price was low. CarFax showed 16 oil changes, so obviously the prior owner took good care of the car. The error codes are 2 Anti-Lock brack Module Codes: C1031 and U3003 Battery Voltage Circuit Voltage Below Threshold. Does anyone know what these codes are?

 

2016, if it has the original battery it "could" be causing both fault codes.
The OEM batteries don't seem to last too long in these vehicles.
Or it could be a sensor, wiring, relay etc. etc. but the battery voltage is easy enough to check.

C1031: Possible CausesFaulty Right Rear Wheel Speed Sensor, Right Rear Wheel Speed Sensor harness is open or shorted, Right Rear Wheel Speed Sensor circuit poor electrical connection. The Anti-Lock Brake System (ABS) control module monitors the voltage at the positive (+) terminal of each sensor while the ignition switch is ON.
U3003: is a generic communication problem with battery voltage. The car has an ABS or Anti brake system control module, hydraulic pump, and solenoid valves that need some voltage to operate

 

As above, have the battery checked. Do NOT use a volt meter, have the battery load tested (for free at places like Autozone). It doesn’t matter how old the battery is, only the load test will tell you the actual battery condition. Modern vehicles (not just Mazda) are very sensitive to battery voltage due to the multiple computers on board, even a slight drop in voltage while running can trip a code. Batteries just don’t last as long as they used to, why? Well we used to run them until they would fail to crank the engine, but today if they fail to run a voltage-sensitive computer we have to replace them.