P0140 code definition
O2 Sensor Circuit No Activity Detected (Bank 1, Sensor 2)
What the P0140 code means
P0140 is the OBD-II generic code which indicates that the O2 sensor for Bank 1, Sensor 2 failed respond to the fuel cutoff or fuel enrichment signals by the Engine Control Module (ECM).
What causes the P0140 code?
The ECM determines that the O2 sensor has no activity
The O2 sensor for Bank 1, Sensor 2 does not respond (does not have a voltage change between 410-490 mV) to the fuel cutoff or fuel enrichment signals from the ECM for more than 74 seconds
The O2 sensor and mass airflow sensor comparison is misinterpreted by the ECM
The ECM could be malfunctioning in the O2 circuit
What are the symptoms of the P0140 code?
The Check Engine Light will come on, indicating a problem
Hesitation (upon acceleration after a deceleration phase)
The ECM loses the ability to keep the fuel system air-to-fuel ratio correct (could cause erratic driving symptoms)
How does a mechanic diagnose the P0140 code?
Scans codes and documents freeze frame data
Monitors the O2 sensor data to see if the voltage is is moving above or below 410-490 mV
Monitors the mass airflow sensor data for responses to throttle changes, per specifications
Follows the manufacturer's specific pinpoint tests for further diagnosis of the code (tests differ between manufacturers)
Common mistakes when diagnosing the P0140 code?
- Check the mass airflow sensor for proper operation and contamination before replacing the O2 sensor.
The no response of the O2 sensor can be caused by a mass airflow sensor being contaminated and not calculating the amount of air entering the engine on the intake side.
How serious is the P0140 code?
This code can be due to problems with the mass airflow sensor, which is needed to calculate the proper amount of air entering the engine. Along with the O2 sensors, failure of any of these components will cause the ECM to miscalculate the air/fuel ratio going into the engine.
The ECM can lose control or get the wrong input from sensors like the mass airflow sensor or the O2 sensor if they are within specification but incorrect.
These problems can cause erratic drive complaints, which can compromise a driver's safety.
What repairs can fix the P0140 code?
After scanning and clearing all fault codes and verifying the failure:
- Test the O2 sensor to see if it changes when the fuel mixture is enriched
- Test the mass airflow sensor for the proper readings per specifications
- Replace the O2 sensor if contaminated or fails tests
- Replace the mass airflow sensor if contaminated or fails tests
- Clean out the mass airflow sensor to see if readings change
Additional comments for consideration regarding the P0140 code
The no response of an O2 sensor may be due to a mass airflow sensor that is contaminated from things like oil from an oil impregnated air filter, as is common to all sensors. This oil coats the sensor and can cause it to become inaccurate. Cleaning the sensor may or may not fix the problem.
Need help with a P0140 code?
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