P0151: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)
P0151 means the upstream oxygen sensor on bank 2 is reporting a voltage that is too low, so the engine computer may be reading the air-fuel mix incorrectly. The most common fix is replacing the bank 2 sensor 1 O2 sensor or repairing its wiring, typically about $150 to $350 at an independent shop.
- Severity
- Moderate
- Can I drive?
- Drive with caution
- DIY?
- Possible with some experience
- Repair cost range
- $100 – $600
Get the answer for your exact car
Add your car and a few details. DashClue asks up to 3 questions, then tells you the most likely cause and what it should cost.
FreeNo card neededAnswer in about 2 minutes
What does P0151 mean?
This code points to the oxygen sensor before the catalytic converter on bank 2, which is the side of the engine without cylinder 1 on a V-type engine. That sensor helps the computer fine-tune fuel delivery by measuring how much oxygen is in the exhaust. If the sensor signal stays low, the computer may think the engine is running lean even when it is not, or it may be getting a bad signal because of a wiring fault or exhaust leak. On many vehicles, the problem is the sensor itself, but wiring damage, poor connections, or a lean engine condition can also set the code.
Common symptoms
- Check engine light on
- Rough idle
- Poor fuel economy
- Hesitation on acceleration
- Loss of power when accelerating
- Strong exhaust smell
Causes, fixes and costs
P0151: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)
General guide for most cars. Your car may differ.
The car usually still runs, but fuel economy and drivability can get worse, and a real engine problem may be hidden. Stop driving if the engine starts misfiring badly, stalling, or the check engine light flashes.
Most likely causes
- 1
Faulty bank 2 sensor 1 oxygen sensorHigh
If the light stays on and the engine runs mostly normal but fuel economy drops or the idle feels a little rough, the sensor itself is often the problem. Heated sensors wear out with age and can stop switching correctly.
Quick check: Look at live data with a scan tool; if the sensor voltage is stuck low or responds very slowly, the sensor is suspect.
- 2
Damaged wiring or connector at the O2 sensorHigh
If the code returns after bumps, rain, or under-hood heat, or if the wiring looks melted, rubbed through, or corroded, the signal may be opening up. Intermittent symptoms often point to harness or connector trouble.
Quick check: Inspect the sensor harness and plug for broken insulation, loose pins, corrosion, or contact with the exhaust.
- 3
Exhaust leak near bank 2 sensor 1Medium
A leak ahead of or near the sensor can pull in outside air and make the sensor read lean or low. This is more likely if you hear ticking, smell exhaust in the engine bay, or the code appeared after exhaust work.
Quick check: Listen for a ticking exhaust leak on cold start and inspect the manifold, gasket, and pipe joints near bank 2.
- 4
Lean engine condition on bank 2Low
If the engine also has lean codes, misfires, or a rough idle, the sensor may be telling the truth. Vacuum leaks, low fuel pressure, or injector problems can create a real low-voltage reading.
Quick check: Check for other lean or misfire codes and inspect fuel trims, vacuum hoses, and fuel delivery.
Can you fix it yourself?
Possible with some experience
Difficulty: Moderate. A careful DIYer can inspect the wiring, check for exhaust leaks, and replace the sensor with the right socket and penetrating oil if access is reasonable. If you need live data, smoke testing, or wiring diagnosis, ask the shop to test the sensor circuit and check for lean conditions before replacing parts.
Show the stepsHide the steps
- Scan for related codes and freeze-frame data
- Inspect the bank 2 sensor 1 connector and harness
- Look for exhaust leaks near bank 2 upstream of the sensor
- Check live data to see whether the sensor is stuck low or slow
- Replace the sensor if testing points to a failed sensor
- Clear codes and road test to confirm the fix
Estimated repair cost
$150 – $350
Bank 2 sensor 1 oxygen sensor: parts ~$50-$180, labor ~$100-$170
- Wiring repair or connector repair$100 – $300
- Exhaust leak repair near upstream sensor$120 – $500
- Diagnose and repair lean engine condition$150 – $600
Prices vary by vehicle, engine layout, and local labor rates.
Frequently asked questions
Can I drive with P0151?
Usually yes for a short time, but you should get it checked soon. If the engine runs rough, stalls, or the check engine light starts flashing, stop driving.
Will P0151 fail an emissions test?
In most places it can fail an emissions or readiness test because the check engine light is on and the engine computer sees a fault. Clearing the code right before a test usually will not help if the issue is still present.
Do I need to replace the oxygen sensor first?
Not always. A wiring problem, exhaust leak, or lean engine condition can set the same code, so a quick inspection and live-data check can save money.
Is bank 2 sensor 1 the upstream sensor?
Yes. Sensor 1 means the upstream sensor before the catalytic converter, and bank 2 is the engine side without cylinder 1 on V-type engines.
Can bad gas mileage be caused by P0151?
Yes. If the engine computer is getting a bad O2 sensor signal, it may add too much fuel or not enough, which can hurt fuel economy.
Related codes
Related problems
This guide covers most cars and is general advice, not an inspection. Prices are typical US independent-shop ranges and vary by region, car and shop. If your brakes, steering or a warning light feel unsafe, stop driving and contact a mechanic.