DTC P0135: Ho2S Heater Performance - Bank 1, Sensor 1: Description

Heated Oxygen Sensors (HO2S) are used in order to minimize amount of time required for closed loop fuel control operation and to allow accurate catalyst monitoring. HO2S heater greatly decreases amount of time required for fuel control sensors to become active. HO2S heater is also required by catalyst monitor sensor to maintain a sufficiently high temperature which allows accurate exhaust oxygen content readings further from engine. PCM will run heater test only after a cold start, and only once during an ignition cycle. A cold start is determined by Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) at time of start-up.

When engine is started, PCM monitors HO2S voltage. When HO2S voltage indicates a sufficiently active sensor, PCM looks at how much time has elapsed since start-up. If PCM determines that too much time was required for HO2S to become active, this DTC will set. Time for HO2S to reach operating temperature is based on ECT at start-up and average Mass Airflow (MAF) since start-up. Higher average airflow or higher start-up ECT equals a shorter time to HO2S activity.