Fuel Trim

FUEL TRIM

Control of the fuel/air mixture occurs using known principles. However the signal from the front probe is now of a linear character. This means that the engine control module (ECM) notices small changes throughout the voltage range and can control the fuel/air mixture much faster and more precisely than before.
Both heated oxygen sensors (HO2S) contain as before a PTC resistor which is supplied with voltage from the engine control module (ECM) in order to reach operating temperature quickly.
If the engine control module (ECM) determines that the ambient air is very cold and damp it may delay starting to heat up the heated oxygen sensors (HO2S) a few minutes. This is to prevent the heated oxygen sensor (HO2S) warm ceramic being touched by cold drops of water and then cracking.
The oxygen sensitive ceramic which measures oxygen levels in the exhaust gases consists of Zirconium dioxide.