What does it mean?
Modern vehicles use both an upstream and downstream oxygen sensor. 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. The downstream oxygen sensor is located behind the catalytic converter and is used to check converter efficiency. It does so by checking the oxygen content of the exhaust after it leaves the converter. For this reason, downstream O2 sensors are known as catalyst monitors. Modern vehicles use heated oxygen sensors (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 P0036 stands for HO2S heater Performance Bank 1 Sensor 2.
This indicates the PCM has detected a problem with heater circuit of the downstream 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. The related code for the other bank is P0056 HO2S Heater Performance Bank 2 Sensor 2. This indicates the PCM has detected a problem with the bank 2 downstream oxygen sensor heater. Oxygen sensor diagram