There is a problem with the rear (post catalytic converter) oxygen sensor.
What P0140 really means:
When the oxygen sensor stops producing voltage, or goes beyond the calibrated voltage, the computer declares a problem. In the majority of vehicles, the rear oxygen sensor acts only as a monitor for catalytic efficiency and does not have any input in fuel management. When the catalytic converter works properly, the oxygen in the exhaust stream measured by this sensor should produce a steady voltage on the rich side of the scale, which indicates the converter is using up oxygen in chemical activity.
What causes a P0140 code?
The rear oxygen sensor acts as the pollution police. Other than telling that the catalytic converter is not doing its job, in most cars, there is little else for it to do. You will not notice any difference in the way the car performs. These sensors go bad over time, especially if the car has small oil or coolant leaks that contaminate the exhaust, so there is little you can do to prevent failure.
What is the severity is a P0140 code?
Minor, however a prudent approach might catch small issues in the converter before they become big.
What repair(s) are needed to resolve a P0140 code?
Replace the rear oxygen sensor. Although the rear oxygen sensor does not change performance in most cars, a mechanic should diagnose the problem. A bad reading in the rear oxygen sensor might be caused by a failing catalytic converter, or it might conceal a converter beginning to fail.
What is the estimated cost to resolve a P0140 code?
- Estimated part(s) cost = $100-150
- Estimated labor cost = $50
- Estimated Total Cost = $150-$200
Comparatively speaking, the replacement of the rear oxygen sensor is not overly expensive. The sensor itself is not as sophisticated as the front one, so the price will be in the $100 to $150 range. The sensors are usually very accessible which keeps the price lower than other equivalent part replacement for labor as well.
Service article written by an ASE Master Technician