P0140 - O2 Sensor Circuit No Activity Detected (Bank 1, Sensor 2)
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0140 is set when the Engine Control Module (ECM) detects a lack of voltage activity from the secondary Oxygen (O2) sensor on Bank 1. After the engine reaches operating temperature and enters closed-loop operation, the ECM monitors the sensor downstream of the catalytic converter. If the sensor voltage remains stationary (typically at the 450mV bias voltage) for a predetermined period, the ECU determines the circuit is inactive. This sensor mainly monitors catalytic converter efficiency.
Possible Causes
Defective O2 sensor (Bank 1, Sensor 2) - internal open circuit
Corrosion or poor connection in the sensor connector
Wiring harness open or shorted in the signal or ground circuit
Faulty Engine Control Module (ECM) or software issue
Symptoms
Recommended Solution
- Visual inspection: Inspect wiring and connectors under the vehicle for mechanical damage or heat damage from the exhaust system.
- Measurement: Monitor sensor signal using a scan tool (Live Data). The voltage should fluctuate when enriching or leaning the mixture. Verify proper ground and 0.45V bias voltage from the ECM.
- Check heater circuit: A failed heater can prevent the sensor from reaching operating temperature. Measure heater resistance (typically 5-15 Ohms).
- Replacement: If wiring is intact but no activity is detected at operating temperature, replace the O2 sensor (Bank 1, Sensor 2). Clear codes and perform a drive cycle.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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