Every one of the 298 codes now has a where-to-start guide

Some codes used to carry a single line of definition. Now every one says what to check first, and why the part is not the first move.

The code reference holds 298 entries, and every one now has a guide — not only what the code means, but where to start checking.

Why this is not «just more text»

A code names the place where the unit saw a mismatch, not the part you should buy. The difference is expensive: P0171 — «lean mixture» — does not mean «the oxygen sensor died»; the sensor honestly reported that there was not enough fuel. Replacing it swaps out an honest witness and leaves the fault in place — there is a separate piece about that.

So every guide follows the same order: cheapest first. What can be checked by hand and eye in ten minutes, and only then what costs money.

What turned out most useful

While writing, a few ideas kept recurring across dozens of codes, and they save the most:

• Connector and wire before the part. A corroded contact gives exactly the same code as a dead sensor and costs nothing. It is the first move for most sensor codes.
• «Internal module error» codes are almost never about replacing the module. They arrive in bunches after a flat battery or a bad earth. Someone who is not told this gets sold a module for the price of a used engine.
• Several codes at once: look for a shared cause. Power, an earth, the bus. Paste them all into the multi-code reader to see where they add up to one cause.
• Half the gearbox codes start with the fluid level and the connector on the outside. Solenoids stick because of dirty fluid far more often than they die.
• Nearly every fuel vapour code starts at the fuel cap. The check takes ten seconds. P0457 names the cause outright rather than the place.

Where to look

The powertrain codes are 249 entries in one list, and browsing it without knowing the code is pointless. So they are split by system: ignition, emissions, the gearbox and five more sections. Each carries its own hints about where trouble in that group usually starts.

If you do not know the code but do know how the car behaves, start with the symptoms: misfiring, hunting idle, rising consumption.

What next

The right move now is not to add codes for the sake of the number, but to improve what is written. One page with an honest guide is worth more than two with definitions.

Guidance is written once for the site and the app alike — it is the same text.