What does it mean?
When you discover a P0150 trouble code stored in your vehicle, it means that the powertrain control module (PCM) has detected a signal voltage input from the upstream (pre catalyst) oxygen (O2) sensor for engine bank two that is inappropriate for a predetermined set of circumstances, during a certain time frame. Bank 2 is the bank of the engine that does not contain the number one cylinder. Sensor one is always the upstream or pre catalyst O2 sensor.
The O2 sensor was invented by Robert Bosch during the 1960s and most, modern, OBD-II equipped automobiles continue to utilize sensors that are either manufactured directly by the Bosch Corporation or mimic the Bosch design. At the heart of the O2 sensor is a zirconium dioxide sensing element enclosed within a vented steel housing. The sensing element is connected (usually with platinum electrodes) to wire leads in the O2 sensor wiring harness.
The connector at the end of the O2 sensor wiring harness is connected to the engine control (controller area network) harness which provides the PCM with real-time data pertaining to the percentage of oxygen in the engine exhaust compared to the oxygen content of ambient air. The upstream O2 sensor is designed to be inserted directly into the exhaust pipe, before the catalytic converter.
The most popular and efficient method of accomplishing this is by threading the sensor directly into a threaded boss that is manufactured into the exhaust pipe. The threaded boss is positioned at the most convenient position and angle for the sensing element and vented steel housing to be inserted. Removal and installation of threaded oxygen sensors will often require specially designed wrenches and sockets, depending upon vehicle application.
Several automakers also use studs welded to the exhaust pipe to secure the sensor so that the sensing element and vented steel housing are inserted into the pipe. Spent engine exhaust gases are pushed through the exhaust manifold and into the exhaust pipe where they pass over the upstream O2 sensor, before reaching the catalytic converter. Exhaust gases flow through specially designed vent holes in the steel housing and across the sensing element.
Ambient air is drawn into a small chamber in the center of the sensor, through the wire lead openings. In the small chamber it is heated, forcing the ions to produce (energy) voltage. Variations between the concentration of oxygen molecules in the exhaust and the ambient air (drawn into the O2 sensor) cause the concentration of the oxygen ions (inside the sensor) to fluctuate.
These fluctuations cause the oxygen ions inside the O2 sensor to reposition from one platinum layer to the other infinitely. The surging oxygen ions cause changes in voltage as they move between platinum layers. These changes in voltage are recognized by the PCM as variations in exhaust oxygen concentration and reflect whether the engine is running lean (too little fuel) or rich (too much fuel).
When more oxygen is present in the exhaust (lean condition) the voltage signal output from the O2 sensor is lower. When less oxygen is present in the exhaust (rich condition) the voltage signal output is higher. This data is used by the PCM to help calculate fuel delivery strategy and ignition timing, among other things. As far as I know, all O2 sensors that are currently used in OBD-II automotive applications are of the heated variety.
Battery voltage is used (as soon as the engine is started) to heat the sensing element so that it can begin providing the PCM with accurate input data more quickly. The heater element passes through the sensing element and is attached to O2 sensor harness wiring with platinum electrodes that resist extreme temperatures created by exhaust gases. The P0150 code does not pertain to the heater portion of the sensor but O2 sensor heater failure can contribute to actual O2 sensor circuit malfunctions.
Upstream O2 sensors typically fluctuate regularly between 100 and 900 millivolts (.1