Wiring connector

The Lambda sensor measures the oxygen content in the exhaust gases: it is fitted on the exhaust pipe upstream of the catalytic silencer.

The sensor output signal is sent to the control unit to correct (feed-back) the mixture strength.

When the sensor supplies a low signal (voltage below 200 mV) the control unit recognizes a lean mixture and increases the injection time; subsequently, when the sensor signal is high (voltage above 800 mV), the control unit recognizes a rich mixture and decreases the injection time.

This sequence of operations is repeated with a frequency in the order of tens of Hertz, so that the engine operates with a mixture strength constantly oscillating around the stoichiometric value.

At temperatures below 300°C the ceramic material is not activated, therefore the sensor does not send reliable signals: to ensure rapid heating during starting and to maintain the temperature during idling, the sensor is equipped with a heater where the electrical resistance is always on.

The sensor can be rapidly put out of action by the presence of even the smallest amounts of lead in the fuel.

The resistance of the sensor heater can be measured by disconnecting the connector and connecting an ohmmeter as shown in the diagram.

Resistance: 4,5 ± 0,5 ohm at 20°C

lambda = 1: stoichiometric mixture
lambda < 1 : rich mixture, the CO values tend to be high
lambda > 1 : lean mixture, the CO values tend to be low

Wiring connector