What does it mean?
A stored code P015B, simply means that the powertrain control module (PCM) has detected a delayed response time from the upstream (before the catalytic converter) oxygen (O2) sensor or circuit for engine bank one. Bank 1 indicates the bank of the engine which contains the number one cylinder. Heated oxygen sensors are constructed with a zirconium dioxide sensing element. It is protected by a vented, steel housing.
Platinum electrodes connect the sensing element to wire leads in the O2 sensor wiring harness. The harness is connected to the PCM through the controller area network (CAN). With the engine at normal operating temperature and running, the PCM is supplied with an electrical signal reflecting the percentage of oxygen particles in the engine exhaust compared to the oxygen content of ambient air. Exhaust gases exit the combustion chambers through exhaust manifold(s) and down pipe(s).
Exhaust then flows through the O2 sensor vent holes (in the steel housing) and across the sensing element. Ambient air is drawn through the wire lead cavities where it is trapped in a small chamber in the center of the sensor. The trapped ambient air (in the chamber) is heated by the exhaust, forcing the oxygen ions to produce (energy) voltage.
Varying degrees in the concentration of oxygen molecules in ambient air (drawn into the center cavity of the O2 sensor) and the concentration of oxygen ions in the spent exhaust gases, cause the heated oxygen ions inside the O2 sensor to jump between platinum layers very rapidly and repetitiously. Fluctuations in voltage occur as the rushing oxygen ions jump between the layers of the platinum electrodes.
These variations in voltage are identified by the PCM as changes in exhaust oxygen concentration which indicate that the engine is either running lean (too little fuel) or rich (too much fuel). When more oxygen is present in the exhaust (lean condition), the voltage signal from the O2 sensor is low and is higher when less oxygen is present in the exhaust (rich condition).
This data is used by the PCM primarily to calculate fuel delivery and ignition timing strategy but also to monitor catalytic converter efficiency. If the O2 sensor in question fails to cycle as rapidly and/or regularly as expected, over a set period of time and under certain predetermined circumstances, a P015B code will be stored and a malfunction indicator lamp may be illuminated.