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EmissionsSeverity Medium: diagnose soon

P0140O2 Sensor Circuit No Activity Detected (bank 1 sensor 2)

What it means

The oxygen sensor bank 1 sensor 2 signal stays flat (around 0.45 V) once the engine is warm. The ECU sees no switching at all. The downstream sensor (after the catalyst) is mainly used to check how well the catalyst works.

Symptoms

  • Check engine light
  • Usually no change in how the car drives
  • Catalyst monitor may not complete

Common causes

  • Open signal circuit
  • Sensor heater not working, so the sensor never gets hot enough
  • Failed sensor
  • Engine never reaching closed loop (e.g. thermostat stuck open)

What to check first

  1. Check the heater circuit and its fuse
  2. Graph the sensor once warm; a flat 0.45 V usually means open circuit
  3. Check that coolant temperature reaches normal
Can I drive with P0140? Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

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P0140: questions and answers

What does P0140 mean?

P0140: O2 Sensor Circuit No Activity Detected (bank 1 sensor 2). The oxygen sensor bank 1 sensor 2 signal stays flat (around 0.45 V) once the engine is warm. The ECU sees no switching at all. The downstream sensor (after the catalyst) is mainly used to check how well the catalyst works.

What are the symptoms of P0140?

Check engine light. Usually no change in how the car drives. Catalyst monitor may not complete.

What causes P0140?

Open signal circuit. Sensor heater not working, so the sensor never gets hot enough. Failed sensor. Engine never reaching closed loop (e.g. thermostat stuck open).

How do you diagnose P0140?

1. Check the heater circuit and its fuse 2. Graph the sensor once warm; a flat 0.45 V usually means open circuit 3. Check that coolant temperature reaches normal

Can I drive with P0140?

Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.