It is the sensor which measures the oxygen concentration after the exhaust gases have been through the cat. The signal is compared with that from the sensor in front of the cat (upstream) to check that the cat is effective.
Either the sensor is defective or a wire in the circuit is broken.
Currently in spacecadet's garage: Laguna 2 1.6 51 plate 5-speed
What the fault code df 083 was saying oxygen sensor heating circuit. New oxygen sensor was not required. Most likely cause of defect loss of 12v feed to heating element within sensor Hth Regards Mickeybo
Currently in mickeybo's garage: 1996 Renault Clio 1.9 Diesel.
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