O2 Sensor Circuit No Activity (Bank 1, Sensor 2)
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.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- easy
- Estimated cost
- $50-$200
Test O2 sensor voltage (should fluctuate 0.1-0.9V). Do not replace a $150 sensor without confirming it is actually bad first.
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Shows real-time O2 sensor readings on your phone. See if the sensor is lazy, stuck, or actually working before spending money.
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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
-
Monitor downstream (Bank 1, Sensor 2) voltage on a scan tool after the engine is fully warm. A healthy downstream sensor produces a slow, lazy signal that drifts above and below about 0.45V -- it should NOT sit pinned at one steady value. A voltage stuck near 0.45V (no activity) is what sets P0140 and points to a failed sensor or open circuit.
-
Test heater circuit resistance.
-
If heater is bad, replace the sensor and retest.
-
Check wiring continuity from sensor to PCM.
Common Fixes by Vehicle
What techs usually find when diagnosing P0140 on specific vehicles — tap your vehicle for the fix and the exact part:
2000-2010 Toyota Camry 2.4L 2AZ-FE easy DIY
Replace Bank 1 Sensor 2 (downstream, post-cat) O2 sensor. Toyota B1S2 Denso OEM only. If replacement doesn't clear within a drive cycle, check for exhaust leak at flex pipe -- air pulls cause downstream sensor to show 'no activity'.
Labor: 30 min2005-2015 Honda Civic/Accord/CR-V easy DIY
Replace downstream (post-cat) O2 sensor with Denso OEM. Honda commonly shows P0140 when pre-cat fails -- verify cat isn't plugged with a tailpipe temperature check. A failing catalyst hides as P0140 before triggering P0420.
Labor: 30 min2007-2014 GM 5.3L/6.0L Trucks (Silverado, Tahoe) easy DIY
Check post-cat O2 harness for rodent damage -- GM harness runs under the cab near the trans, squirrels love it. Repair chewed wires with solder + heat shrink before replacing sensor. If harness is intact, replace B1S2 with AC Delco.
Labor: 45 minFrequently 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.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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