DTC P0161: 2/2 O2 Sensor Heater Malfunction (4.0L With CALIF. Emissions): Description

2/2 Heated Oxygen Sensor (HO2S) heater voltage is monitored with engine at idle for at least 12 seconds after a cold start, battery voltage is more than 9 volts, engine coolant temperature is less than 147°F (63.9°C) and ambient/battery temperature is within 27°F (-3°C) plus or minus of engine coolant temperature. DTC will set in Powertrain Control Module (PCM) memory when PCM senses 2/2 HO2S voltage is more than 3 volts for 30-90 seconds. Possible causes for DTC to set are: blown fuse, defective HO2S downstream heater relay, defective PCM, defective connectors or defective wiring.