Car Mechanics (UK)


- Belgium · Caterpillar

Fit­ted to ev­ery new petrol car by law since the early 1990s, three-way reg­u­lated cat­alytic con­vert­ers have proven to be very re­li­able. They work by con­vert­ing harm­ful ni­tro­gen ox­ide, car­bon monox­ide and hy­dro­car­bons into, pri­mar­ily, ni­tro­gen, car­bon diox­ide and water.

As the pre­cious platinum/ rhodium/pal­la­dium met­als that coat the del­i­cate hon­ey­comb struc­ture within the con­verter (as shown) do not change them­selves, they are very lon­glast­ing. How­ever, they are not tol­er­ant of sud­den im­pacts or rapid cool­ing (such as driv­ing though flood water).

‘Cat theft’ has also be­come an is­sue, due to high scrap prices, es­pe­cially on taller ve­hi­cles. As a num­ber of re­place­ment after­mar­ket con­vert­ers con­tained hardly any pre­cious met­als, to keep the price down, it be­came a le­gal re­quire­ment for all cat­alytic con­vert­ers to meet cer­tain stan­dards, be Type Ap­proved and wear the ap­pro­pri­ate E-marks. Even so, coun­ter­feit con­vert­ers can still be bought, es­pe­cially for older cars that were pop­u­lar be­fore the Type Ap­proval re­quire­ment be­came law, so be wary of very cheap of­fer­ings avail­able on­line, in par­tic­u­lar.

Most diesel cars have been fit­ted with un­reg­u­lated ox­i­dis­ing cat­alytic con­vert­ers for more than 20 years. These play an ex­tra func­tion on cars equipped with DPFS, be­cause they pro­mote an exother­mic re­ac­tion that helps to in­crease DPF tem­per­a­tures and this fa­cil­i­tates soot com­bus­tion.

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