DTC P0136: 1/2 O2 Sensor Heater Circuit Malfunction (4.0L With CALIF. Emissions): Description

1/2 Heated Oxygen Sensor (HO2S) heater voltage is monitored after ignition is turned on and voltage is more than 10.4 volts. DTC will set in Powertrain Control Module (PCM) when PCM senses relay control circuit between PCM and relay coil does not match desired state. Possible causes for DTC to set are: blown fuse, defective HO2S downstream heater relay, defective PCM, defective connectors or defective wiring.