DTC P0134: Ho2S Circuit - Insufficient Activity (Bank 1; Sensor 1 - SOHC): Description
WARNING: This page is about a different car, the 2002 Pontiac Sunfire, 2002 Pontiac Grand Am, 2002 Oldsmobile Alero, and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
The Powertrain Control Module (PCM) supplies a voltage of approximately 0.45 volt between the Heated Oxygen Sensor (HO2S) 1 high signal and the low signal circuit. The HO2S 1 varies the voltage within a range of approximately 1 volt if the exhaust is rich, to approximately 0.1 volt if the exhaust is lean.
The sensor is like an open circuit and does not produce any voltage if the temperature is less than 600°F (315°C). An open sensor circuit or a cold sensor causes an open loop operation.