O2 Sensor Signal Biased/Stuck Lean (Bank 2)
Indicates that the O2 sensor in Bank 2 is reporting a lean mixture consistently.
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What it means (plain English)
The Oxygen (O2) sensor on one side of the engine is saying that there's too much air and not enough fuel in the exhaust, meaning the engine's running too lean.
What the computer is actually seeing
The Engine Control Module (ECM) is interpreting the O2 sensor's voltage output as consistently low, typically under 0.1 volts while the expected range is around 0.2-0.8 volts during normal operation.
What a healthy reading looks like
O2 sensor voltage should fluctuate between 0.2 to 0.8 volts during normal operation; if it's stuck near 0.1 volts for extended periods, it's likely biased lean.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check for any vacuum leaks around the intake manifold or vacuum hoses. Repair any leaks found.
- 2Inspect the wiring and connectors to the Bank 2 O2 sensor for damage or corrosion.
- 3Test the O2 sensor operation by using a scanner to monitor the voltage output while the engine is running. It should fluctuate between 0.2 and 0.8 volts.
- 4If the O2 sensor shows a steady low voltage (near 0.1 volts), replace the O2 sensor and retest.
- 5Check fuel pressure; it should be within manufacturer specifications. If low, diagnose the fuel pump and filter.
Common causes
- Faulty O2 sensor
- Vacuum leak in the intake system
- Fuel delivery issues (low fuel pressure, clogged filter)
- Exhaust leaks before the O2 sensor
- Wiring issues (frayed wires, bad connectors)
Typical repair cost
$$-$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's generally drivable but fix soon; running lean can cause engine damage if ignored.
Will this code come back after clearing?
It may come back if the underlying cause isn't fixed.
Why do I see this code alongside P0136?
Both codes can indicate issues with O2 Sensors; P0136 is for Bank 1 while P219B is for Bank 2.
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