Centre Oxygen Sensor
The wiring to the oxygen sensors must not be squeezed or in any other way damaged. It is also not allowed to grease the contacts for the oxygen sensors as the oil in the grease would interfere with the reference air and the function of the oxygen sensors. Even the area where the cable harness connects to the oxygen sensor body must be protected from contamination for the same reason.
The centre oxygen sensor is basically identical to the rear oxygen sensor and is only found on versions with three oxygen sensors. The oxygen sensor is located after the first stone in the catalytic converter and is instead used for the rear oxygen sensor while waiting for it to become sufficiently hot.
Preheating element
Heating works in the same way as for the rear oxygen sensor. The centre oxygen sensor has, however, a stronger heating coil to get the full functionality of the measurement more quickly. The Heating time for the centre oxygen sensor is short, about 30 - 40 seconds.
The oxygen sensor, including heating element, can be diagnosed by the Engine Control Module (ECM), and signals from the oxygen sensor can be read out.