What does it mean?
The upstream oxygen sensor (O2S) is located ahead of the catalytic converter. It is used to determine the concentration of oxygen in the exhaust gas. This information is used by the PCM to control the engine air/fuel mixture. The sensor compares amount of oxygen in the exhaust to the surrounding air (there is an opening in the sensor that is exposed to the atmosphere). It generates a corresponding voltage which is transmitted to the PCM. The PCM then controls injector pulse based on this value.
Modern vehicles use a heated oxygen sensor (HO2S). These sensors contain a heating element that brings the sensor to operating temperature faster. This allows the PCM to use the signals input sooner, for more precise fuel control and reduced emissions. The heater circuit is energized through a relay that closes when the engine is cranked. The PCM monitors the heater circuit and will turn on the check engine light if it finds a problem.
Code P0135 stands for Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1). This indicates the PCM has detected a problem with the bank 1 oxygen sensor. Bank 1 refers to the side of the engine that has the #1 cylinder. Bank 2 is the opposite side of the engine. If you’ve got a four-cylinder, there will only be one bank. A typical heated oxygen sensor