6.6 - Oxy (Lambda) Sensors ( ,  )

These devices are fitted into the exhaust downpipe and measure the oxygen content of the exhaust gasses. For correct operation it requires operation of an inbuilt heater element and a reference atmosphere, which is obtained from normal air entering along the wiring harness. The device changes resistance dependent on the exhaust gasses and this change is measured by the ECU. Note this is different to earlier models, where the sensor produced a small voltage for the ECU to measure.

European models have two sensors, one in each downpipe. US specification models have four sensors, with the second pair fitted after the catalytic converters to allow the ECU to monitor their effectiveness.

If sensors are removed, ensure each is connected to the correct location and wiring, otherwise the ECU cannot understand the behaviour of the engine and will set a check engine error code.

When the engine is in warm-up, the ECU ignores the sensors and operates using a reference set of information. Once sufficient temperature has been reached, the ECU will begin to use the sensor outputs to control the precise fuel/air mixture of the engine.

In correct operation, probing the voltage with a DVM should show it continuously swinging between 0V and 5V. The component is easy to damage chemically, so do not use solvents such as WD40 to clean the connectors.

The wiring for the sensors is routed to the rear of the engine over the transmission bellhousing, located in place by metal clips. If the oxy sensors appear ineffective, resulting in high CO% readings, check the insulation hasn't frayed at the clips and effectively earthed the sensor.