Technical Description of OBD-II Trouble Code
Malfunction in the O2 Sensor Circuit (Bank 2 Sensor 1)
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to vehicles equipped with OBD-II. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The O2 sensor generates a voltage based on the oxygen content in the exhaust. The voltage ranges between .1 and .9 Volts, with .1 indicating a lean mixture and .9 indicating a rich mixture. Sensor #1 is the first sensor located downstream from the engine.
The ECM (Engine Control Module) continuously monitors this voltage while in closed loop to determine the amount of fuel to inject. If the ECM determines that the O2 sensor voltage was too low (less than .4 Volts) for an extended period of time (more than 20 seconds, time varies with model), this code is triggered. The code P0150 refers to Bank 2.
Potential Symptoms
Depending on whether the problem is intermittent or not, there may be no symptoms other than the illumination of the MIL (malfunction indicator lamp). If the problem is constant, then symptoms may include one or more of the following:
Causes
Usually, a faulty oxygen sensor is the cause of P0150, but this is not always the case. If your O2 sensors have not been replaced and they are old, it is likely that the sensor is the problem. However, it could also be caused by any of the following:
Possible Solutions
Using a scan tool, determine if Bank 2, sensor 1 is switching properly. It should rapidly alternate between rich and lean mixtures.
1. If it is switching properly, the problem is likely intermittent. Examine the wiring for any visible damage and perform a wiggle test by manipulating the connector and wiring while observing the O2 sensor voltage. If the voltage drops out, repair the affected part of the wiring harness.
2. If it is not switching properly, try to determine if the sensor is accurately reading the exhaust. Do this by briefly removing the vacuum supply to the fuel pressure regulator. The O2 sensor reading should become rich, indicating a response to the additional fuel. Reinstall the regulator supply and induce a lean condition by removing a vacuum supply line from the intake manifold. The O2 sensor reading should become lean, indicating a response to the leaner exhaust. If the sensor operates properly, then the sensor may be functioning correctly and the problem may be holes in the exhaust or an unmetered vacuum leak in the engine (NOTE: Unmetered vacuum leaks at the engine are almost always accompanied by lean codes. Refer to the appropriate articles for diagnosing an unmetered vacuum leak). If there are holes in the exhaust, it is possible that the O2 sensor may misread the exhaust due to the additional oxygen entering the pipe through those holes.
3. If none of the above is the case and the O2 sensor is not switching or is sluggish, unplug the sensor and ensure that there is a 5 Volt reference voltage to the sensor. Then check for a 12V supply to the O2 sensor’s heater circuit. Also check for continuity to ground on the ground circuit. If any of these are missing or are not at their proper voltage, repair any open or short in the appropriate wire. The O2 sensor will not function properly without the correct voltage. If the proper voltages are present, replace the O2 sensor.
