O2 Sensor Circuit No Activity Bank 1 Sensor 2
Diagnostic trouble code P0140 indicates that the engine control module (ECM) has detected no activity from the downstream oxygen sensor on Bank 1. The ECM sets this code when the sensor's voltage signal remains stuck at a steady baseline and fails to fluctuate during normal driving conditions.
This code primarily affects emissions monitoring rather than engine performance. While it is safe to drive with this code in the short term, the vehicle will not pass an emissions inspection until it is resolved.
Common symptoms
- Illuminated Check Engine Light
- Failed state emissions test
- Incomplete OBD-II readiness monitors
- Slight decrease in fuel economy
- Usually no noticeable drivability issues
Likely causes
- Faulty Bank 1 Sensor 2 oxygen sensor
- Damaged, melted, or corroded wiring and connectors to the sensor
- Blown oxygen sensor heater circuit fuse
- Exhaust leak near the downstream oxygen sensor
- Faulty Engine Control Module (ECM)
What to check before replacing parts
Visually inspect the wiring and connector for Bank 1 Sensor 2.
Look for: Look for melted, chafed, or disconnected wires, as well as corrosion or water intrusion inside the electrical connector.
Check the fuse for the oxygen sensor heater circuit.
Look for: A blown fuse indicates a short in the heater circuit, which can prevent the sensor from reaching operating temperature and becoming active.
Monitor the O2 sensor voltage using a scan tool with live data.
Look for: Observe the Bank 1 Sensor 2 voltage; if it remains stuck at approximately 0.45V and does not change when the throttle is snapped, the sensor or circuit is inactive.
Test the resistance of the oxygen sensor's internal heater element using a multimeter.
Look for: An open circuit (infinite resistance) or a reading outside of the manufacturer's specified range indicates a failed sensor that requires replacement.
Inspect the exhaust system near the catalytic converter and downstream sensor for leaks.
Look for: Look for black soot marks or listen for hissing/ticking sounds that indicate outside air is entering the exhaust stream and skewing the sensor readings.
This page explains the generic P0140 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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