P0151
O2 Sensor Circuit Low Voltage Bank 2 Sensor 1.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 1
- AreaFuel and air metering
- 51
- FaultThe specific fault in that area
What it means
P0151 means the control unit has seen a persistently low signal voltage from the upstream oxygen sensor (Bank 2, Sensor 1), the one fitted before the catalytic converter on the side of the engine opposite cylinder 1. The signal has stayed below the expected range, typically near or below about 0.1 volts, rather than switching between rich and lean as it should. The fault may be in the sensor, its heater or wiring, or a genuine lean running condition on that bank.
Symptoms
- Check engine light on
- Poor fuel economy or rough running
- Hesitation or poor acceleration
- Rough idle or occasional misfire feel
- Failed emissions test
- Fuel trim readings stuck lean or at their limits on Bank 2
Possible causes
- Ageing or contaminated upstream oxygen sensor on Bank 2 giving a lazy or low signallikely
- Exhaust leak upstream of the sensor letting in air and giving a false lean readinglikely
- Vacuum leak or unmetered air entering on Bank 2, causing a genuine lean mixturelikely
- Damaged, chafed or corroded wiring or connector to the sensor, including a short to ground or sensor reference or signal wire issuespossible
- Low fuel pressure or a restricted or faulty injector on Bank 2 causing a lean conditionpossible
- Faulty mass airflow sensor or other airflow measurement fault causing incorrect fuellingpossible
- Fault in the engine control unit sensor circuitrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting engine load, temperature and fuel trims when the fault set
- Check for other related codes such as lean codes, misfire codes or airflow sensor codes, and deal with those first
- Inspect the Bank 2 sensor wiring and connector for damage, heat damage, water ingress, corrosion and poor pin tension
- Look and listen for exhaust leaks near the manifold, flexible joint and sensor mounting on Bank 2
- Check for vacuum leaks and induction leaks, such as split hoses, intake manifold gaskets and the crankcase breather system
- View live data: compare Bank 2 Sensor 1 voltage and fuel trims against Bank 1, and check whether the sensor switches when you briefly enrich or lean the mixture
- Check fuel pressure and injector operation against the manufacturer's specification for the model and engine
- Test the sensor circuit for supply, ground and signal faults using the manufacturer's wiring diagram and procedure
How to fix
- Repair or replace damaged wiring or the connector on the Bank 2 sensor circuit
- Repair any exhaust leak upstream of the sensor
- Fix any vacuum or intake air leaks found, such as perished hoses or leaking gaskets
- Replace the Bank 2 Sensor 1 oxygen sensor if it is confirmed faulty or contaminated, after finding the cause of any contamination
- Correct fuel delivery faults such as low fuel pressure or a faulty injector on that bank
- Replace a faulty airflow sensor if testing shows it is reading incorrectly
Can I keep driving?
The car can usually be driven for a short time, but a lean mixture can raise combustion temperatures and harm the catalytic converter, so get it checked soon. Avoid heavy loads and long journeys, and stop if the engine runs badly or misfires.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.