DTC P0133: Front Heated Oxygen Sensor Circuit, Slow Response: Condition

WARNING: This page is about a different car, the 2002 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set when front HO2S response rate is below predetermined level. Possible causes are:

Front HO2S coated with contaminants.
Exhaust leak.
Open or shorted circuit.
Improper fuel.
Faulty MAF sensor.
Leak in air induction system.
Deteriorating front HO2S.