Monitoring of the oxygen situation is performed with the oxygen sensor located in the exhaust manifold through the feedback to the ECM; the ions can vary an air/fuel mixture and instantly adjust the ratio for the maximum efficiency and minimal emission, with the optimum coefficient of 14.7 to 1. If the sensor is open, then it develops a Code 13, a low or high voltage issue causes the engine to run on open loop creating Codes 44 and 45. For the sensor to work correctly it must have good electrical connection; it must not be choked with excess air; it must come to operating temperature of about 600 °F (315°C) and should preferably use unleaded fuel. This requires a sharp focus during servicing not to damage the permanently attached pigtail and connector, do not let contaminants get near the electrical parts, do not use cleaning solvents, and ensuring that silicone boot is properly placed. In case of replacement, the sensor is fitted in a different location depending on the type of engine and must not be replaced if the engine is cold or below 120°F. The location of the silicone boot should be observed and the sensor pulled back very gently just to avoid stripping the threads. To facilitate easy unfastening at a later stage, some threads on the sensor require an anti-seize compound with the sensor subsequently tightened to the required torque and connected to the main engine wiring harness.