OBD-II Code · Sensors
P0151
O2 Sensor Low Voltage (B2S1)
Severity
medium
Worth booking. It costs fuel, emissions or comfort until it is fixed.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$150–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Bank 2 upstream sensor voltage low.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Likely causes
- Lean conditionMost common
- Failed sensor
- Wiring
Read the full diagnostic procedureP0151 is bank 2 upstream signal stuck LOW — same diagnostic as P0131 but on the other bank.
P0151 is bank 2 upstream signal stuck LOW — same diagnostic as P0131 but on the other bank.
Scan fuel trims first
- if B2 STFT + LTFT are pegged at +20 to +25%, the engine is really running lean on bank 2 and the sensor is correctly reporting it.
- That points to a bank-2-specific vacuum leak (intake manifold runner gasket on a V6, valve cover gasket on bank 2 only, cracked PCV hose routed to bank 2 intake), a bank-2 fuel delivery issue (one injector on bank 2 partially clogged, or a cracked fuel rail), or a bank-2 exhaust leak upstream of the sensor introducing fresh air.
- If fuel trims are normal, the signal is being pulled low by wiring — backprobe and check for shorts to ground.
- Critically: confirm bank assignment from the FSM before you smoke-test or replace anything.
Vehicle-specific patterns2005-2010 Ford F-150 5.4L 3V — bank 2 is passenger side; throws P0151 from cracked exhaust manifolds on passenger side specifically (the well-known b…
- 2005-2010Ford F-150 5.4L 3V — bank 2 is passenger side; throws P0151 from cracked exhaust manifolds on passenger side specifically (the well-known broken-manifold-stud TSB).
- 2007-2014GM 3.6L LFX/LLT — transverse, bank 2 is front; throws P0151 from a torn front intake-manifold-runner gasket.
- 2008-2014Dodge Avenger / Journey 3.5L SOHC — sets P0151 when the front (bank 2 transverse) intake plenum gasket fails.
- 2009-2016Audi A4/A6 3.0T supercharged — sets P0151 from a leaking T-fitting on the bank 2 PCV hose. Cost band: $200-$500 for sensor; $300-$1,200 if the actual cause is a manifold or VCG leak.
Look up another code
P0151 — frequently asked
What does a P0151 code mean?
Bank 2 upstream sensor voltage low.
What causes a P0151 code?
Common causes: Lean condition; Failed sensor; Wiring.
What are the symptoms of a P0151 code?
Typical symptoms: Check engine light.
Is it safe to drive with a P0151 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $150-$400.
How do I diagnose a P0151 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
More free tools