P0151
O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)
The PCM sees the front oxygen sensor on bank 2 reporting too little voltage. That can happen when the engine is actually running lean, when the sensor is biased low, or when wiring or exhaust leaks affect the reading. Because this is the upstream sensor, it can interfere directly with fuel control.
- SEV
- 3/5
- DRIVE
- CAUTION
- DIY
- $20-$250
- SHOP
- $120-$650
Quick answer
AI-CITATION READYWhat it means
Can you drive with it?
Most common causes
- Vacuum leak, intake leak, or other true lean-running condition on bank 2
- Exhaust leak ahead of the Bank 2 Sensor 1 oxygen sensor
- Faulty or biased-low Bank 2 Sensor 1 oxygen sensor
Typical repair cost
DIY usually runs $20-$250. Typical shop repair lands around $120-$650, depending on the root cause.
01 / Definition
P0151 means the PCM detected a low-voltage condition in the oxygen-sensor signal circuit for Bank 2 Sensor 1. This is the upstream sensor before the catalytic converter on the side of the engine that does not contain cylinder 1. The low signal can be caused by a lean air-fuel mixture, exhaust leak, weak sensor, wiring fault, or heater problem that keeps the sensor from responding normally.
02 / Drive status
With caution. Short trips are usually possible, but the engine can run lean, hesitate, or lose fuel-control accuracy. Diagnose it soon because a real lean condition can lead to drivability complaints or catalyst damage over time.
03 / Symptoms
- Check engine light on
- Poor fuel economy
- Rough idle or hesitation
- Possible lean surge on light throttle
- Failed emissions test
04 / Causes
| 1 | Vacuum leak, intake leak, or other true lean-running condition on bank 2 | high |
|---|---|---|
| 2 | Exhaust leak ahead of the Bank 2 Sensor 1 oxygen sensor | high |
| 3 | Faulty or biased-low Bank 2 Sensor 1 oxygen sensor | high |
| 4 | Damaged wiring, poor ground, or connector corrosion in the sensor circuit | medium |
| 5 | Heater-circuit issue slowing sensor warm-up or response | medium |
05 / Diagnostic sequence
- 01Verify P0151 and check freeze-frame data plus related fuel-trim or misfire codes.
- 02Inspect for vacuum leaks, cracked hoses, intake leaks, or exhaust leaks ahead of Bank 2 Sensor 1.
- 03Review live data for Bank 2 Sensor 1 and compare it with Bank 1 Sensor 1 if the engine has two banks.
- 04Inspect the sensor connector and wiring for heat damage, corrosion, oil contamination, or poor ground.
- 05Confirm the heater circuit is working so the sensor can warm up and switch normally.
- 06Test fuel pressure or injector balance if the engine may truly be running lean on bank 2.
- 07Replace the sensor only after mixture, exhaust, and wiring faults are ruled out.
06 / Repairs
| 1 | Repair vacuum leaks, intake leaks, or exhaust leaks affecting Bank 2 Sensor 1 readings | $20-$300 |
|---|---|---|
| 2 | Repair wiring, connector, or ground faults in the Bank 2 Sensor 1 signal circuit | $20-$150 |
| 3 | Replace the Bank 2 Sensor 1 oxygen sensor if testing shows it is biased low or slow to respond | $70-$280 |
| 4 | Correct fuel-delivery or injector problems if bank 2 is truly running lean | $100-$500 |
07 / Related codes
08 / FAQ
What does Bank 2 Sensor 1 mean on P0151?
It is the upstream oxygen sensor before the catalytic converter on the side of the engine that does not contain cylinder 1.
Does P0151 always mean the engine is lean?
No. A bad sensor, wiring fault, or exhaust leak can create a low-voltage reading even if the mixture is not truly lean.
Can I keep driving with P0151?
Usually for short trips, but it should be diagnosed soon because true lean running can hurt drivability and converter life.
09 / Source and method
- DATA BASIS
- OBD-II REFERENCE + OBD2.HELP
- METHOD
- STATIC VALIDATION
- SAFETY
- INFORMATIONAL
This page combines OBD-II diagnostic reference data with OBD2.help generated diagnostic guidance for code meaning, likely causes, and repair direction.
Publishing uses deterministic schema and build validation, plus manual spot checks on representative pages before release.
Safety-critical diagnosis and repairs should be confirmed with a qualified mechanic, especially when the vehicle is misfiring, overheating, or losing power.