Exhaust Gas (Oxygen) Sensor

Sensor measures amount of unburned oxygen in exhaust gases. When heated in the presence of exhaust gases, sensor provides a voltage signal which is used to adjust air/fuel mixture (amount of injection time), so that optimum combustion can occur. Two types of oxygen sensor are used.

G20 and Q45 use a Zirconia oxygen sensor which, when heated in the presence of exhaust gases, produces a varying voltage signal relative to oxygen content of exhaust gases. Sensor also contains an additional heating circuit in order to bring sensor quickly to operating temperature. Ground for heating element is controlled by ECU. Two oxygen sensors are used on Q45.

M30 uses a Titania oxygen sensor, which is a type of resistor. ECU provides Titania oxygen sensor with a 1-volt reference signal. Resistance of ceramic Titania varies when subjected to lean and rich conditions. A rich exhaust gas mixture causes sensor resistance to drop and a lean exhaust gas mixture causes sensor resistance to increase.

ECU monitors signal from oxygen sensor and adjusts air/fuel mixture based upon this signal. Sensor also contains an additional heating circuit to quickly bring sensor to operating temperature.