Lambda sensors

Oxygen Sensors - System Applications | A 15Oxygen Sensors - System ApplicationsWhy are there sensors before and after the catalytic converter?Fig. 1 - Diagnosis Sensor voltage output - typicalFig. 2 - Control Sensor voltage output - typicalSince the introduction of ADR 36 in 1986 requiring all newpassenger vehicles to operate on unleaded fuel inAustralia, there has been constant improvement andevolution of engine management systems. This majorchange also saw the introduction and broad use of oxygensensors and catalytic converters. Starting with fairly simpleapplications using one single wire sensor in the exhaustmanifold, over the years multiple sensors for “V”configuration engines have been implemented providingmore efficient air/fuel ratio control and diagnosticcapabilities.In recent years in Australia, there has been a rapid increaseof vehicles using pre and post catalytic converter oxygensensors. These are referred to in this catalogue as Control(pre catalyst) and Diagnosis (post catalyst) oxygen sensors.The requirement for controlling the combustion process isnow only one of the functions of the engine managementsystem. Modern systems also control and monitor theoperation of the vehicle’s catalytic converter. With thefitment of sensors after the catalyst, the efficiency of thecatalytic converter can now be evaluated and various enginecontrol strategies can be employed to reduce harmfulexhaust emissions throughout various driving and engineoperating conditions.Diagnosis Sensor Operating Characteristics.Whilst the diagnosis sensor is often of the same designfamily as the conventional control sensor, sensor activityis quite different to what would be expected of a correctlyoperating pre-catalyst sensor. As shown in fig. 1, theoutput signal from the diagnosis sensor is generally a flatoutput signal of approximately 500mV, this is in contrastto the control sensor normal activity as shown in fig. 2.2009 | 2010 Bosch Automotive Aftermarket