P0150
PowertrainO2 Sensor Circuit Malfunction (Bank 2 Sensor 1)
Most of the time this is the upstream oxygen sensor on bank 2 packing up, either the sensor itself dying with age or a corroded plug behind it. P0150 means the ECU has seen the signal voltage from that sensor sitting outside the range it expects, so it can no longer trust it to help set the fuel mixture. Bank 2 sensor 1 is the front sensor on the cylinder bank that doesn't contain cylinder number 1, which only matters on V6 and V8 engines.
ⓘ Information only. This page provides general educational information about fault code P0150. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0150 mean?
P0150 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: O2 Sensor Circuit Malfunction (Bank 2 Sensor 1).
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on the dash, often the first and only thing you notice
- • Fuel economy creeping down, roughly 5-10% worse and more obvious on longer runs
- • Rough or lumpy idle, sometimes worse from cold before the engine has warmed through
- • Hesitation or a flat spot when you put your foot down
- • Black smoke or a strong fuel smell from the exhaust if the mixture has gone rich
- • Misfiring or stalling in the worst cases, when the ECU has lost a sensor it relies on
Possible causes
Causes commonly associated with P0150, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Worn out oxygen sensor on bank 2 sensor 1, the usual culprit on higher mileage cars as the element ages and the signal goes lazy or dead
- 2. Damaged or corroded wiring and connector at the sensor, common where the loom runs close to the exhaust heat
- 3. Faulty heater circuit inside the sensor, so it never reaches operating temperature and the ECU sees no proper signal
- 4. Exhaust leak ahead of the sensor pulling fresh air in and skewing the reading
- 5. Contaminated sensor element from burnt oil, coolant or the wrong fuel additives coating the tip
- 6. Vacuum leak upsetting the air-fuel mixture enough to confuse the readings
- 7. Less common: an ECU calibration fault or a damaged module, worth checking only after everything else is ruled out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Pull the live data on the scanner and watch the bank 2 sensor 1 voltage with the engine warm. A working sensor swings between about 0.1V and 0.9V. If it sits flat or doesn't move, the sensor or its wiring is the problem.
- 2. Get under the car and check the sensor plug and the wiring running back from it. Look for melted insulation, green corrosion in the connector, and chafing where the loom touches the exhaust.
- 3. Test the heater circuit resistance with a multimeter, you're looking for roughly 2-5 ohms across the heater terminals. An open circuit there points straight at a dead sensor.
- 4. Check the exhaust around the bank 2 manifold and flange for leaks. A blowing joint upstream of the sensor will give false readings that look exactly like a failing sensor.
- 5. If the signal is fine and the wiring is clean, look at fuel trims and check for a vacuum leak before you condemn anything expensive.
- 6. Only after all that comes good should you start thinking about ECU diagnostics or a firmware update.
Common questions about P0150
Will my car fail its MOT with a P0150 stored? +
The code on its own isn't a direct MOT failure, but if the engine warning light is lit when the tester plugs in or eyeballs the dash, that can count against you. The bigger risk is the emissions test. If the sensor is feeding the ECU rubbish the mixture can drift rich, and your CO and HC readings may push over the limit. Sort the sensor, drive a few cycles to clear the light, then book the test.
What's it likely to cost to put right? +
If it's just the sensor, a decent aftermarket part runs £40-£120 and an independent garage will usually fit it for £80-£180 all in. A main dealer fitting an OE sensor can easily double that. If the trouble turns out to be wiring repairs, exhaust work or any ECU diagnostics, you're looking at the higher end and the bill climbs quickly. Get the diagnosis nailed before you authorise anything.
How do I know if it's the sensor itself or the wiring on my car? +
Watch it live. With the engine warm, a healthy sensor voltage dances between 0.1V and 0.9V on the scanner. A signal stuck at one value usually means a dead sensor or a broken heater circuit, which you can confirm with the 2-5 ohm resistance check across the heater pins. If the signal cuts in and out as you wiggle the connector, your problem is the wiring or the plug, not the sensor.
Can I just clean the sensor or fix it myself? +
Cleaning an oxygen sensor rarely works and isn't worth the faff. The element either reads correctly or it doesn't, and once it's contaminated or worn it needs replacing. Fitting a new one yourself is fair game if you've got an oxygen sensor socket and can reach the bank 2 location, which on some transverse V6 layouts is buried at the back and a real knuckle-skinner. Spray the threads with penetrating oil the night before and take your time.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →