Can a vacuum leak cause P0151?

Yes. A leak on the bank 2 side lets in air the engine computer has not measured, so that bank runs lean and its upstream sensor reads low. A vacuum leak usually also pushes the bank 2 fuel trims up and often sets P0174 as well. A smoke test is the quickest way to find it.

Is P0151 the same as P0131?

It is the same fault on the other bank. P0131 is low voltage from the upstream sensor on bank 1, the bank with cylinder 1, and P0151 is low voltage from the upstream sensor on bank 2. Only engines with two banks can set P0151.

Can I drive with P0151?

For short distances, yes. Expect worse fuel economy and possibly a hesitation. If the cause is a real lean condition, it can get worse and lead to misfires, so have it diagnosed within days rather than weeks. Stop driving if the check engine light flashes.

Which sensor is Bank 2 Sensor 1?

It is the upstream oxygen sensor, the one before the catalytic converter, on the half of the engine that does not contain cylinder 1. Most V6, V8 and flat-six (boxer) engines have two cylinder banks, each with its own upstream sensor. A few inline-sixes with two exhaust manifolds, such as BMW's M54, also split into bank 1 (cylinders 1-3) and bank 2 (cylinders 4-6). Which physical side is bank 2 differs between makers, so check the service information for your engine before you order a part.

P0151: O2 Sensor Circuit Low Voltage (Bank 2, Sensor 1)

Quick Answer

Safe to drive (short-term)

P0151 means the upstream oxygen sensor on bank 2 has reported a low voltage for too long, which reads as too much oxygen in the exhaust, a lean mixture. Bank 2 is the half of a V6, V8 or flat-six engine that does not contain cylinder 1 (a few inline-sixes with a split exhaust, such as BMW's M54, also have one). It is the same fault as P0131 on the other bank. The cause is either a real lean condition on that bank, such as a vacuum or exhaust leak, or a sensor or wiring fault that makes the signal read low.

Severity: Moderate · Emissions
Estimated repair cost: From €45 to €320+, varies by vehicle

Scan your own car in about 60 seconds: see whether P0151 is really what it has, how urgent it is, and what the fix should cost. Free on iPhone and Android with an ELM327 adapter (Bluetooth LE on iPhone).

Get Skanyx free

What does P0151 mean?

P0151 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0151 and illuminates the check engine light.

Where it is on the car

Engine
Oxygen sensor before the converter (sensor 1)
Catalytic converter
Oxygen sensor after the converter (sensor 2, or 3 on some cars)
Silencer and tailpipe

This code is for bank 2. V6, V8 and flat engines have two cylinder banks, each with its own converter and sensors; bank 2 is the side without cylinder 1.

What are the symptoms of P0151?

If your vehicle has triggered P0151, you may notice one or more of these symptoms:

Check engine light on
Hesitation or stumble under acceleration
Rough or unstable idle
Higher fuel consumption
Failed emissions test
Possible P0174 (System Too Lean, Bank 2) stored at the same time

What causes P0151?

Here are the most common causes of P0151:

Failing or aged upstream O2 sensor on bank 2
: high
Vacuum leak on the bank 2 side (intake gasket, hose, crankcase breather) causing a real lean mixture
: high
Exhaust leak ahead of the bank 2 sensor drawing in outside air
: medium
Signal wire shorted to ground or damaged connector at the bank 2 sensor
: medium
Weak or clogged fuel injector on a bank 2 cylinder
: low
Sensor contaminated by coolant, oil or silicone sealant
: low

Is it safe to drive with P0151?

Generally yes, for short-term driving. You can drive to a workshop, but do not leave it for weeks. A genuine lean condition on bank 2 can cause hesitation and misfires, and the engine computer may add extra fuel to compensate, which raises fuel consumption and can harm the catalytic converter over time. If the check engine light flashes or the engine misfires, stop driving.

How do you diagnose P0151?

Follow these steps to pinpoint the root cause of P0151:

Read all stored codes and freeze frame data. P0174 alongside P0151 points to a real lean condition on bank 2. P0171 and P0174 together point to something both banks share, such as the MAF sensor, fuel pressure or a large intake leak
Warm the engine and compare Bank 2 Sensor 1 with Bank 1 Sensor 1 on live data. A narrowband sensor stuck below about 0.2 volts while the bank 1 sensor keeps switching points at bank 2
Check short- and long-term fuel trims for each bank. High positive trims on bank 2 only mean the engine computer is adding fuel to that bank, which supports a real lean condition rather than a sensor fault
Smoke-test the intake. Look for leaks at the intake manifold gaskets, vacuum hoses and crankcase breather on the bank 2 side
Inspect the exhaust between the bank 2 cylinder head and the sensor for leaks, cracks or a loose flange
Inspect the bank 2 sensor wiring and connector for chafing against the exhaust or body that could short the signal to ground
If trims are normal and no leaks are found, replace the bank 2 upstream sensor, clear the code and confirm it stays off after a drive cycle

How much does P0151 cost to fix?

Repair costs for P0151 vary depending on the root cause and your vehicle. Here are typical estimates:

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Replace upstream O2 sensor (Bank 2, Sensor 1)	€40–€180	€50–€140	€90–€320	Moderate
Fix vacuum leak on the bank 2 side	€10–€60	€40–€150	€50–€210	Moderate
Repair exhaust leak ahead of the bank 2 sensor	€15–€80	€50–€200	€65–€280	Moderate
Repair O2 sensor wiring or connector	€5–€25	€40–€120	€45–€145	Moderate

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

Full repair guides

Oxygen Sensor Replacement Cost

P0151 on specific vehicles

P0151 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0151 on Mercedes-Benz

Mercedes-Benz C-Class (V6)

See Mercedes-Benz-specific causes & cost

P0151 on BMW

BMW 5 Series (545i/540i/550i) · BMW 3 Series (E46 325i/330i)

See BMW-specific causes & cost

These codes are often seen alongside P0151 or indicate related issues:

Common questions about P0151

What does P0151 mean?: P0151 means the upstream oxygen sensor on bank 2 has read low voltage for longer than the engine computer allows. Low voltage means the sensor sees a lot of oxygen, which reads as a lean mixture. Either that bank really is running lean, or the sensor or its wiring is giving a false low signal.
Can a vacuum leak cause P0151?: Yes. A leak on the bank 2 side lets in air the engine computer has not measured, so that bank runs lean and its upstream sensor reads low. A vacuum leak usually also pushes the bank 2 fuel trims up and often sets P0174 as well. A smoke test is the quickest way to find it.
Is P0151 the same as P0131?: It is the same fault on the other bank. P0131 is low voltage from the upstream sensor on bank 1, the bank with cylinder 1, and P0151 is low voltage from the upstream sensor on bank 2. Only engines with two banks can set P0151.
Can I drive with P0151?: For short distances, yes. Expect worse fuel economy and possibly a hesitation. If the cause is a real lean condition, it can get worse and lead to misfires, so have it diagnosed within days rather than weeks. Stop driving if the check engine light flashes.
Which sensor is Bank 2 Sensor 1?: It is the upstream oxygen sensor, the one before the catalytic converter, on the half of the engine that does not contain cylinder 1. Most V6, V8 and flat-six (boxer) engines have two cylinder banks, each with its own upstream sensor. A few inline-sixes with two exhaust manifolds, such as BMW's M54, also split into bank 1 (cylinders 1-3) and bank 2 (cylinders 4-6). Which physical side is bank 2 differs between makers, so check the service information for your engine before you order a part.

Read our detailed guides

Scan your car with Skanyx to diagnose P0151

Your car logged P0151. Skanyx reads it on a standard OBD2 adapter (Bluetooth LE on iPhone), tells you whether it is safe to keep driving, and shows the €45-€320 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.