What is the P0140 trouble code?
3 Answers
P0140 trouble code indicates that the oxygen sensor circuit is inactive, specifically for the second oxygen sensor in Bank 1. Possible causes include: 1. Exhaust manifold or exhaust pipe leakage. 2. Faulty oxygen sensor, its circuit, or connector. 3. Malfunction in the electronic control module (PCM or ECM), etc. Additional considerations: After troubleshooting, promptly clear the trouble code. Clearing the trouble code should be performed by a professional; do not use the method of disconnecting the battery negative ground cable to clear the trouble code, as this may cause the vehicle's computer to lose its learned memory, resulting in certain vehicle functions becoming inoperable, reduced performance, and potential long-term repair difficulties or recurrence of the trouble code after driving for a period.
P0140 trouble code indicates no activity signal from the downstream oxygen sensor in the engine control system, most commonly occurring at Bank 1, Sensor 2 position. Simply put, it means a sensor in the exhaust system has failed and can't monitor oxygen levels—possibly due to a faulty sensor, broken wiring, or computer error. I often encounter this during repairs, with the most common causes being sensor aging or water intrusion at the connector, especially after rainy days or car washes. If left unfixed, fuel consumption may increase by about 20%, emissions won't meet standards, and it harms the environment by polluting the air. Diagnosis isn't difficult: first read the trouble code, check the sensor connector and wiring voltage—if those are normal, the sensor needs replacement. Though a minor code, it affects overall engine efficiency. Regular vehicle maintenance can prevent this issue.
Last time my car's check engine light came on, and the code P0140 showed up. Turned out it was a problem with the downstream oxygen sensor. It's located in the rear section of the exhaust system and controls emissions. After it failed, I noticed a significant increase in fuel consumption. Once while driving on the highway, the engine light started flashing, so I pulled over immediately to check and found that the wiring had been chewed through. After the repair, emissions returned to normal, and fuel efficiency improved. I recommend paying attention to warning lights while driving daily—don't ignore trouble codes to avoid costly repairs to the engine or catalytic converter later. For a quick DIY check: visually inspect the sensor's position for any looseness or corrosion.
