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.
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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
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.
-
Check the sensor heater circuit -- if the heater has failed, the sensor may never reach operating temperature.
-
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.
-
If wiring is intact, replace the O2 sensor.
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.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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