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.
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
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 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'. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
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.
What actually makes the computer set an oxygen sensor code?
The OBD II regulation requires four separate detections for an oxygen sensor (Title 13 CCR 1968.2, section (e)(7.2)): deterioration in voltage, response rate or amplitude that would push emissions past 1.5 times the FTP standards; loss of circuit continuity; out-of-range values; and the case where the sensor has degraded enough that the fuel system stops using it and falls back to open loop. A sensor can therefore set a code while still producing a signal that looks plausible on a scan tool. This is the threshold the monitor is designed around, not a description of your specific fault — the regulation says what the system must detect, not how to find it on your vehicle.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
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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.
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Test heater circuit resistance.
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If heater is bad, replace the sensor and retest.
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Check wiring continuity from sensor to PCM.
Sources 3
This page is built from documented references. Verify against your own service info before repair work.
- California Code of Regulations, Title 13 section 1968.2 (OBD II)malfunction criteria, section (e)
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- Ford Mustang and Taurus
- Toyota Tacoma
- Honda Element
- Nissan Frontier
- Chevrolet Malibu
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