Twenty reference sections: catalyst, canister, soot filter

The «emission controls» heading held 41 codes: the catalyst, exhaust gas recirculation, the charcoal canister, the fuel level and the particulate filter. Five different repairs and five different prices — in one list.

Somebody holding a P0455 has no business among particulate filter codes, and a diesel owner with P2458 has none among canister codes. So we sorted them out.

What has appeared

Exhaust gas recirculation (EGR) — 7 codes. The valve, its actuator and the position sensor.

Secondary air injection — 3 codes. A system that runs for ninety seconds a day — and can still fail the car at an emissions test.

Catalytic converter — 4 codes. The former «emission controls» address stayed alive and narrowed to the catalyst: P0420 is the most searched code of the whole group.

Canister and purge valves — 9 codes.

Fuel vapour leaks — 7 codes. The size of the leak is stated in the name of the code: large, small or very small.

Fuel level in the tank — 4 codes.

Diesel particulate filter — 6 codes.

One code that fitted nowhere

The cooling fan relay P0480 sits in the fourth group by number — among the emission codes — while by meaning it belongs neither to the catalyst nor to the canister. It went to the auxiliary systems, where it belongs. The layout now handles such exceptions: a section can be given a narrow extra tail without breaking its main group.

The numbers

There are now 20 sections, against eight a week ago. The reference holds 298 codes, none outside a section and none in two at once. Every code page shows which section it belongs to, and the check verifies that with one code per section.