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P0151 points to the upstream O2 sensor on bank 2 (the side WITHOUT cylinder #1). Because this is the upstream sensor, it directly drives fueling - a stuck-low reading often means a real lean condition, not a sensor problem. Check fuel trims first. See O2 sensor sockets on Amazon ↗
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0151 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
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🎯 Top Causes & Probability
35%
#1 - Most Likely
Bank 2 Lean Condition (Vacuum Leak / Low Fuel Pressure)
A vacuum leak on the bank 2 intake side, a partially clogged injector, or low fuel pressure makes bank 2 actually run lean - the sensor is reporting accurately. Check long-term fuel trims on bank 2; values above +10% confirm a true lean condition that needs fixing before touching the sensor.
🔩 Part
$15–$300
👨🔧 Labor
$50–$300
⚡ DIY Difficulty
Medium
30%
#2 - Check First
Failed Upstream O2 Sensor (Bank 2, Sensor 1)
The bank 2 upstream sensor has failed and is stuck at low voltage. Common past 80k–100k miles. Replacement resolves the code if fuel trims look normal otherwise.
🔩 Part
$40–$220
👨🔧 Labor
$50–$150
⚡ DIY Difficulty
Easy
20%
#3 - Less Common
Exhaust Leak on Bank 2 Upstream
A cracked exhaust manifold or leaking gasket between the engine and the bank 2 upstream sensor pulls in fresh air, making the sensor read lean. V6 and V8 exhaust manifolds are especially crack-prone on the bank closer to the firewall.
🔩 Part
$50–$400
👨🔧 Labor
$150–$600
⚡ DIY Difficulty
Hard
10%
#4
Wiring Damage / Shorted Signal Wire
Burned or chafed wiring on the bank 2 sensor harness, or a signal wire grounded to the chassis, holds the voltage low. Inspect the harness routing near hot exhaust components.
🔩 Part
$5–$60
👨🔧 Labor
$50–$150
⚡ DIY Difficulty
Medium
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Read Bank 2 Long-Term Fuel Trim - Connect a scan tool and check LTFT on bank 2. Above +10% confirms a real lean condition - chase that cause (vacuum leak, fuel pressure, injector) first. Below +10% with a stuck-low sensor points to the sensor itself.
- Smoke Test the Bank 2 Intake Side - If trims are lean, smoke-test the intake on the bank 2 side specifically. PCV hoses, intake gaskets, and brake booster vacuum lines are common culprits.
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need