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P0140 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


Error code P0140: Problem in Oxygen Sensor Circuit


The error code P0140 appears when there is a significant problem in your vehicle’s post catalytic oxygen sensors. The DTC error code P0140 suggests that the inbuilt oxygen sensors have malfunctioned, and there is no activity in Bank 1’s Sensor 2. These oxygen sensors are placed behind the catalytic converter, which controls exhaust emissions. The oxygen sensors monitor and evaluate the intensity of exhaust from the convertor. The data and values the oxygen sensors record are interpreted by the car’s Power Control Module (PCM). The PCM controls the converted emissions and alters the engine’s overall performance. If oxygen sensors malfunction, the car’s Power Control Module would log the DTC error code P0140. 

The car’s exhaust emissions system functions on the data logged by oxygen sensors. Oxygen sensors work at optimum voltage ranges, depending on the oxygen content. Catalytic converters send low voltage if they detect substantial oxygen content and vice versa. Controlled exhaust emissions will be released if your vehicle’s catalytic converter is working at its best efficiency. The DTC error code P0140 appears when the O2 sensors do not detect oxygen values in specified ranges. 


The inbuilt oxygen sensors in Bank 1 act as pollution indicators that send constant signals to the main ECM. Any malfunction in O2 sensors affects the working efficiency of the catalytic converter and causes error code P0140. To deduce the primary cause, one should thoroughly examine the bank 1 and O2 sensors. Below are the possible reasons that might trigger error code P0140.

  • Malfunctioned or damaged sensors
  • Problem in primary circuit and wiring 
  • Hardware or software problem in main Power Control Module (PCM)
  • Frayed wires and connectors
  • Melted harness due to direct heat from the exhaust
  • Moisture in harness connector
  • Accumulated carbon and soot on sensors


As the PCM detects the DTC error code P0140, it notifies the driver by the illuminated check engine light. With time, every vehicle’s catalytic convertor loses its efficiency to control emissions. However, the error code P0140 does not affect the overall drivability of the vehicle. Nonetheless, you need to repair it to avoid unforeseen problems.Mentioned below are the likely problems one can experience:

  • Illuminated check engine light on the dashboard
  • Increased gas emissions from the silencer or the tailpipe
  • Failed and incomplete vehicle emission test
  • Compromised air to fuel ratio
  • Noise in air injection system pump
  • Fluctuations in the engine while accelerating and decelerating


It is imperative to conduct a thorough and detailed inspection of your vehicle to deduce major problems causing error code P0140. The car’s PCM would also detect problems during the self-start and notify the driver. While carrying out the initial diagnosis, one can look for compromised or burnt wiring in the primary sensor’s circuit. After a preliminary self-analysis, one can remove the accumulated soot or carbon from the O2 sensors. It is best to refer to your car’s manual before conducting a thorough self-analysis. Every automobile brand has its specified error codes and their potential causes. The self-diagnosis may include the following steps: 

  • Start the ignition and scan for error code using OBD-II Scanner
  • Check for frayed connections and harness connector
  • Look for fuses and connectors
  • Visually suspect heater and O2 sensors
  • Clean and repair the ground circuit

A professionally experienced motor technician analyze the error code P0140 using an OBD-II scanner. Moreover, the mechanic would search for potential reasons that caused the catalytic converter to malfunction and produce the DTC error code P0140. The auto mechanic or the electrician would visually analyze the wiring, circuits, connectors, and fuses attached to the O2 sensors. The mechanic can also reset the entire PCM and check whether the code reoccurs. The automobile mechanic or the motor-technician  would follow the steps below to diagnose the problem causing the DTC error code P0140:

  • The mechanic would use an OBD-II scanner to decode the error from the PCM. While scanning the PCM, the mechanic would freeze the previous frame data to diagnose the root cause issue. The frozen frame data would highlight the potential failures that cause error code P0140
  • After the initial diagnosis with the OBD-II scanner, the mechanic would visually check Bank 1 circuits, wiring, and connectors. Moreover, he would also check the carbon emissions released during the ignition
  • Next, the mechanic would monitor the voltmeter readings and check whether the O2 sensor voltage is within the ideal range of 410-490 mVThe auto mechanic technician would monitor the mass airflow data and evaluate variable throttle changes. The air injectors and O2 sensors also need to be replaced if necessary
  • The automobile technician would further check the value of resistance between the terminals and the circuit’s ground
  • The mechanic would conduct a detailed inspection after going through the user manual as every brand has different specifications

Common Mistakes in Diagnosis:

With the DTC error code P0140 occurs, there’s a fair chance that the O2 sensors and their circuits are compromised. While examining the error code P0140, a mechanic should check for airflow sensors and injection pumps before replacing them. Moreover, the burnt wires and connectors need repairing or replacing before changing the entire air injection pump and its circuit. The mechanic should also look for contamination and moisture on O2 sensors.

How Serious is the DTC P0140 Error Code?

If the error code P0140 persists, it can directly malfunction and impact the mass airflow sensor. The airflow sensors regulate and maintain the volume and flow of incoming air in your vehicle’s engine. At times, replacing the motor and wiring isn’t the correct solution. It is important to closely check all fittings, sensors, circuits, and fuses linked to oxygen sensors. If error code P0140 isn’t resolved, it would certainly impact your vehicle’s average fuel consumption and overall efficiency. 

How to Fix This?

To enjoy a hassle-free drive, one should always maintain their vehicle according to the instructions mentioned in the car owner’s manual. It is imperative to deduce the root cause of the error code P0140 and then replace sensors and integrated circuits linked to them. Moreover, it is advisable to consult a certified motor technician who uses an OBD-II scanner to evaluate the primary cause of error code P0140.


Every motor engine and its integrated parts need regular maintenance and cleaning. It is essential to maintain your vehicle’s overall health and condition to avoid DTC error codes. Before replacing the entire circuit and O2 sensors, one should consult a qualified mechanic to get the right advice. The error code P0140 needs to be fixed on a priority basis to avoid engine malfunction and excessive fuel consumption.

P0140 Code – What Does It Mean & How To Fix It