P0151: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)
The upstream oxygen sensor on bank 2 is stuck reading low voltage, which looks like lean exhaust on that side of the engine.
What P0151 means
P0151 is the bank 2 match to P0131. The upstream sensor on the side of the engine opposite cylinder 1 is staying below about 400 millivolts for longer than the computer allows, which signals a lean exhaust on that bank. As RepairPal explains for this family of codes, the exact time and voltage limits vary by maker, and on wideband air-fuel sensors the code means the sensor stayed lean biased too long. The engine may really be lean on bank 2 because of an intake gasket leak or vacuum leak on that side, or the sensor may be reading false because of an exhaust leak or a failing element. When P0174 is set at the same time, the lean condition is probably real. Shops compare both banks on a scan tool, add propane to see whether the sensor responds, and smoke test the intake and exhaust. A sensor that does not react gets replaced; a sensor that reacts normally points to a leak or fuel problem instead.
Common symptoms
- Check engine light on
- Hesitation or rough idle
- Lower fuel economy
- May appear with P0174
- Failed emissions test
Most common causes
- Failing bank 2 upstream oxygen sensor
- Exhaust manifold leak on bank 2
- Vacuum leak on bank 2
- Signal wire shorted to ground
- Low fuel pressure
What to check yourself first
If P0174 is also set, focus on vacuum leaks and fuel delivery first. Check for exhaust leaks at the bank 2 manifold. Inspect the sensor wiring for heat damage.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace oxygen sensor | $440-$523 | When the sensor will not respond to added fuel. |
| Smoke test for vacuum or exhaust leaks | $61-$90 | Finds vacuum or exhaust leaks on bank 2. |
| Replace intake manifold gasket | $683-$834 | If the intake gasket on bank 2 is leaking. |
| Electrical diagnosis to find a wiring or connector fault | $122-$179 | For a shorted wire. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
Related repair guides
- Tundra in Limp Mode With Code P2440 or P2442? The Air Injection Pump Problem Explained
- Ram 1500 Ticking on Cold Start? Broken Exhaust Manifold Bolts, Repair Cost and What to Ask
Related codes
- P0150 O2 Sensor Circuit (Bank 2 Sensor 1)
- P0174 System Too Lean (Bank 2)
- P0131 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)
- P0155 O2 Sensor Heater Circuit (Bank 2 Sensor 1)
- P0430 Catalyst System Efficiency Below Threshold (Bank 2)