O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 3)
The P0146 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 3). This is a low severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $80 - $300 (O2 sensor $60-$200; labor $50-$150)
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
- No noticeable drivability symptoms
- Catalyst monitor readiness will not complete
- Failed emissions test
- Slightly increased emissions
Probable Causes (Ranked by Likelihood)
- Failed O2 sensor producing no signal Very High
- Open circuit in the sensor signal wiring High
- Disconnected or corroded sensor connector Moderate
- O2 sensor heater failure preventing warm-up Moderate
- PCM signal circuit fault Low
Frequently Asked Questions
Can I drive with code P0146?
Yes, you can drive normally. Sensor 3 is used for post-catalyst monitoring only and does not control fuel delivery.
What does no activity detected mean?
The PCM expects the O2 sensor voltage to fluctuate as exhaust composition changes. When the voltage stays fixed and does not move, the PCM determines there is no sensor activity, indicating the sensor has failed or is not connected.
Is P0146 the same as P0140?
They are the same type of fault -- no activity detected -- but for different sensors. P0140 is bank 1 sensor 2, while P0146 is bank 1 sensor 3. Not all vehicles have a sensor 3.
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
-
Monitor sensor 3 voltage on a scan tool. If the reading is stuck at approximately 0.45V (mid-range) and never fluctuates, the sensor has no activity.
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Check the sensor heater circuit -- if the heater has failed, the sensor may never reach operating temperature.
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Disconnect the sensor and check signal wire continuity from the connector to the PCM.
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Inspect the connector for corrosion, pushed-out pins, or water damage.
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If wiring is intact, replace the O2 sensor.
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
- 2005-2013 Toyota Avalon (3.5L V6)
- 2007-2015 Lexus IS350 (3.5L V6)
- 2008-2016 Honda Pilot (3.5L V6)
- 2006-2014 Ford Explorer (4.0L V6)
- 2009-2017 Nissan Pathfinder (3.5L V6)
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