What Does P0150 Mean?
The upstream O2 sensor on Bank 2 (Bank B, Sensor 1) is not cycling properly between rich and lean voltages. The PCM expects this sensor to oscillate between high (rich) and low (lean) voltage readings as the fuel system operates in closed loop, but the switching pattern is outside the expected parameters. This is the primary fuel control sensor for Bank 2 and directly affects air-fuel ratio management. The driver may notice poor fuel economy and rough engine performance.
Common Causes
40%
Failed or degraded upstream O2 sensor on Bank 2 with abnormal switching behavior
20%
Vacuum leak or air leak on Bank 2 intake causing a persistent lean condition
15%
Exhaust leak near the Bank 2 exhaust manifold introducing ambient air
15%
Fuel delivery issue on Bank 2 — clogged injector or low fuel pressure
10%
Sensor wiring fault, open signal wire, or corroded connector
Diagnostic Steps
1
Monitor Bank 2 Sensor 1 O2 voltage at 2500 RPM — the sensor should oscillate between 0.1V and 0.9V at a rate of 1-3 Hz; a fixed voltage or extremely slow cycling confirms the fault.
2
Check Bank 2 short-term and long-term fuel trims — trims more than +/-10% indicate the PCM is compensating for an underlying air-fuel ratio issue separate from the sensor.
3
Perform a propane enrichment test near the Bank 2 intake and exhaust — introduce propane and verify the sensor responds immediately by going rich (above 0.7V).
4
Inspect exhaust manifold and connections on Bank 2 for leaks — use a smoke machine or spray soapy water on joints while running.
5
Disconnect the sensor and measure internal resistance and heater resistance — signal leads should show high impedance (100K+), heater should be 2-25 ohms.
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
The upstream O2 sensor on Bank 2 (Bank B, Sensor 1) is not cycling properly between rich and lean voltages. The PCM expects this sensor to oscillate between high (rich) and low (lean) voltage readings as the fuel system operates in closed loop, but the switching pattern is outside the expected param...
The most common cause of P0150 (Oxygen Sensor Cycle Fault, Engine Bank B, Upstream of Catalytic Converter) is: Failed or degraded upstream O2 sensor on Bank 2 with abnormal switching behavior
Typical repair costs for P0150 range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive with caution. An upstream O2 sensor that isn't cycling properly means the PCM cannot accurately control fuel delivery for Bank 2, potentially leading to lean misfires, catalytic converter damage, or rich running that wastes fuel. Repair soon.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0150 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel System / Emissions
Difficulty
Type
Generic (SAE)
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