What does the code C1223 mean when the Check.

Hello,

C1223 Left Rear Wheel Speed Sensor Input Signal Is Zero this means the wheel speed sensor when out or the connection got dirty/corroded.

Here is a guide so you can test the sensor

https://www.2carpros.com/articles/abs-wheel-speed-sensor-test

you will need to use a jack as well

https://www.2carpros.com/articles/jack-up-and-lift-your-car-safely

Here is what it's like to change on your car (Below)

Please let us know what you find.

Cheers, Ken