Car Mechanics (UK)

LAMBDA/OXY­GEN SEN­SORS

- Belarus · Robert Bosch · Volvo Cars · Belgium · Iceland · Volvo 262

In­vented by Bosch and fit­ted first to the Fed­eral-specificat­ion Volvo 200-series in the mid-1970s, Lambda sen­sors can now be found on many mod­ern ve­hi­cles. They are crit­i­cal to cat­alytic con­verter longevity and ef­fec­tive­ness, be­cause the con­verter works only in very nar­row air/fuel mix ra­tios, the op­ti­mum of which is known as ‘Lambda 1’ or 14:1. Lambda/oxy­gen sen­sors de­tect the ex­haust gases’ oxy­gen con­tent, prompt­ing the en­gine ECU to ad­just the fuel/air mix­ture ac­cord­ingly.

As Lambda ra­tio is con­sid­ered dur­ing an MOT test, note that the value is cal­cu­lated. Any leak in the ex­haust sys­tem might cause the Lambda value to be in­flu­enced suf­fi­ciently to cause an MOT fail. The sen­sors tend to be re­li­able, although they fail with time and can be ‘poi­soned’ by exposure to gly­col – be wary of Lambda sen­sor dam­age if your en­gine has suf­fered from head gas­ket fail­ure, for ex­am­ple.

Take care when fitting a new Lambda sen­sor. Not only are they frag­ile, but also their plugs and ca­bles should be kept away from heat sources. ELTA Au­to­mo­tive rec­om­mends that new sen­sors are fit­ted when­ever you fit a re­place­ment ex­haust sys­tem/cat­alytic con­verter, not only be­cause the ex­ist­ing items can be dam­aged eas­ily, but be­cause they also have a fi­nite life of be­tween about 45,000 miles for an un­heated sen­sor and 100,000 miles for a heated type.

Once an old sen­sor is un­screwed (not­ing that you can buy ded­i­cated Lambda sen­sor sock­ets from sup­pli­ers such as Laser and Draper) and you are not plan­ning to re­place the pipe, clean the threads with a suit­able tap to re­duce the risk of over­tight­en­ing the new part, which risks crack­ing the sen­sor’s internal ce­ramic wall (on heated de­signs). Most new Lambda sen­sor threads are pre-greased and ap­ply­ing cop­per grease is not rec­om­mended, be­cause you risk con­tam­i­nat­ing the sen­sor nose and un­der-tight­en­ing the part as a con­se­quence. Should more than one Lambda sen­sor be fit­ted, re­place them all to­gether.

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