Check engine light

P0140 - Oxygen Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

First inspect the exhaust system for leaks ahead of the catalytic converter. Next, view the signal voltages coming from the other three oxygen sensors once the engine is warmed up. The two front sensors should switch between "rich" and "lean" about twice per second. The two rear sensors should switch typically about once per every minute or two. If the Engine Computer is happy with how the right rear sensor is responding, the goal is to have the left one do the same thing. If both front sensors are developing similar signal voltages, that proves both sides of the engine are using the same amount of fuel, then, if both catalytic converters are working, the two rear sensors should be reporting similar values. When one rear sensor is not developing a signal voltage, it is usually due to a failed sensor, but before a mechanic will just throw a part at the problem and hope it fixes it, he will introduce an artificial rich and lean condition to see how the sensors respond.