P0151 code: O2 Sensor Circuit Low Voltage (Bank 2, Sensor 1)
P0151 means o2 Sensor Circuit Low Voltage (Bank 2, Sensor 1). The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0151 means
This is the Bank 2 twin of P0131: the upstream oxygen sensor on the bank opposite cylinder 1 (V-type and flat engines only) is reporting a voltage stuck low — a continuous lean reading — for longer than the computer accepts. Since Sensor 1 is the fuel-control sensor for its bank, the computer may respond by adding fuel or by dropping that bank out of closed-loop control entirely. The sensor itself is the most frequent cause, but a genuine lean condition on Bank 2 (a vacuum leak on that side of the intake, for example), an exhaust leak near the sensor drawing in outside air, or a signal wire shorted to ground can all look identical. Comparing Bank 1 and Bank 2 fuel-trim data is the quickest way to tell a lying sensor from a genuinely lean bank.
P0151 symptoms
- Check-engine light
- Reduced fuel economy
- Rough or uneven idle, sometimes hesitation
- Failed emissions test
What it costs to fix P0151
Typical range: $150–$600 · about ~0.3–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Upstream oxygen (O2) sensor | $50–$250 | ~0.3–1.5 hrs |
| Exhaust leak repair near the sensor | $20–$200 | ~0.5–2 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
Sensor price is ordinary; access is the variable. Bank 2's upstream sensor is notoriously buried on some transverse V6 layouts, pushing labor toward the high end, while on longitudinal V8s it can be as easy as Bank 1.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0151 for my exact vehicle →
How to fix P0151
Moderate — doable at home with common tools and patience
- Compare fuel trims between the two banks
On live data, put Bank 1 and Bank 2 long-term fuel trims side by side. Bank 2 trim climbing far higher than Bank 1 says that bank is genuinely running lean; trims that look similar on both banks say the sensor is lying — this one comparison steers the whole diagnosis.
- If Bank 2 reads genuinely lean, hunt for a vacuum leak on that side
Inspect intake gaskets, vacuum hoses, and connections on the Bank 2 side of the engine, listening for hissing. Unmetered air entering one bank leans it out and drags its upstream sensor low without the sensor being at fault.
- Check for an exhaust leak near the Bank 2 sensor
Look and listen around the Bank 2 manifold and the sensor's bung for soot trails or cold-start ticking. A leak upstream of the sensor pulls in outside air between exhaust pulses and reads as a false lean.
- Inspect the sensor's wiring for a ground short
Trace the Bank 2 upstream sensor harness for sections pinched against the block or melted on the manifold. A signal wire shorted to ground holds the voltage low continuously and mimics a dead sensor exactly.
- Replace the Bank 2 upstream sensor
With trims normal and no leaks or wiring damage found, the sensor has failed — the most frequent outcome. Fair warning on access: on some transverse V6 layouts this sensor is buried against the firewall, so assess reachability before committing to the driveway.
DIY or shop? The fuel-trim comparison and leak checks are excellent DIY diagnosis, and on longitudinal V6/V8 engines the sensor swap is straightforward. Where it tips to a shop is access — some transverse V6s bury the Bank 2 upstream sensor badly enough that a lift makes the difference — or when trims confirm a genuine lean condition, since pinpointing a vacuum leak properly calls for a smoke machine.
Tools for the DIY steps: OBD-II scan tool with live fuel-trim data · O2 sensor socket · Penetrating oil · Long extensions and swivels · Flashlight and inspection mirror
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0151.
Start a case with P0151 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0151?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0151: common questions
Is P0151 the same as P0131?
Same fault, opposite side of the engine: P0131 is low voltage from the Bank 1 upstream sensor, P0151 from the Bank 2 upstream sensor. Only V-type and flat engines have a Bank 2, so this code never appears on an inline four.
How do I know if it's the sensor or a real lean condition?
Compare fuel trims between banks with a scan tool. If Bank 2's trims are heavily positive while Bank 1 looks normal, that bank may genuinely be lean — think vacuum leak on that side. If trims look similar on both banks, suspicion shifts to the sensor and its wiring.
Can I drive with P0151 for a while?
A code alone can't clear the car, but here's the urgency: the engine runs less efficiently, and weeks are a reasonable window for the repair; months are pushing it, since poor fuel control slowly punishes the catalytic converter on that bank.
Why is this sensor expensive to replace on my V6?
On transverse V6 engines, Bank 2 usually faces the firewall, and its upstream sensor can be difficult to reach without removing other parts. The sensor costs the same as any other — the difference is labor time.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0151 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0151 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.