Four new step-by-step guides, linked from the code pages

Catalyst, thermostat, EGR and a code that comes back after a reset. Until now a guide could only be found in its own section.

The «How to» section now holds 13 guides instead of 9. The four new ones cover what people most often ask in words rather than by code.

What was added

The code came back after a reset. Clearing a code and fixing the car are different things. The guide covers why an empty fault list right after a reset proves nothing, why you should look at readiness, and how a code returning in ten minutes differs from one returning in three days.

Check the catalyst with the oxygen sensors. Compare behaviour, not numbers: with a healthy catalyst the rear sensor stays flat instead of copying the front one's swings. And separately — why you should look for misfires before replacing a catalyst.

Tell whether the thermostat is to blame. By warm-up time and by what the temperature does afterwards. Plus how to tell a lying sensor from a stuck thermostat.

Check the EGR valve with live data. Command and error are read together; a sooted valve differs from blocked passages in that the command is there while the engine's behaviour does not change at all.

The texts are not the main part

Until now a guide could be reached almost only from its own section: the code page carried two links, both the same for all 298 codes. Someone arriving from search on the catalyst page did not find the catalyst guide — even though it was written.

Now the code page and the live-data page point to the matching guide themselves: P0420 to the catalyst, P0128 to the thermostat, P0401 to the EGR. The same from the readings: lambda, coolant temperature, EGR command.