P0140 moderate

O2 Sensor Circuit No Activity (Bank 1, Sensor 2)

What does P0140 mean?

The P0140 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Circuit No Activity (Bank 1, Sensor 2). This is a moderate severity code.

Common Symptoms

  • Check Engine Light on
  • Emissions test failure
  • No catalyst monitoring data
  • Possible P0420 triggered

Probable Causes (Ranked by Likelihood)

  • Failed downstream O2 sensor Very High
  • Heater circuit failure preventing sensor warm-up High
  • Open signal wiring Moderate
  • Exhaust leak neutralizing the sensor signal Low

Step-by-Step Diagnostic Procedure

  1. Monitor downstream sensor voltage during a highway drive. Should show steady signal in the 0.6-0.8V range.

  2. Test heater circuit resistance.

  3. If heater is bad, replace the sensor and retest.

  4. Check wiring continuity from sensor to PCM.

Frequently Asked Questions

Is P0140 the same as a dead catalytic converter?

No. P0140 means the downstream O2 sensor is not producing data. P0420 is the code for catalyst inefficiency. A failed downstream sensor must be replaced before evaluating catalyst condition.

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