P0133 Signal Period for Oxygen Sensor Ageing.
Oxygen sensor aging is determined by the DME by monitoring the period (oscillating frequency) of the sensor signal. With an old sensor, the duration of the period is too long.
Reasons for this could be frequent driving in the lower load range (city driving, short distances, etc.) or a contaminated sensor. Bad wiring could be a issue but typically you'd get no signal rather than a degraded signal if the wiring was bad.
Clear the code and see if it returns. If so, then you may have to replace it.
Good reading here:
https://sites.google.com/site/mikefocke2/oxygensensors