What a code tells you

Tapping a code opens the screen this whole app exists for. A code number on its own is not information. What you need is what it means, what the engine was doing when it happened, and what to check first.

The plain English line

At the top is the code, and under it what it actually means in a sentence you can act on. P0171 reads as a lean fuel mixture on bank one rather than “System Too Lean Bank 1”, because the second version is the thing you were going to have to translate anyway.

Conditions when this happened

This is freeze frame, and it is the most underused thing in any scan tool.

At the moment a fault sets, the engine computer photographs itself: engine speed, load, coolant temperature, vehicle speed, fuel trims, whatever that vehicle stores. The app shows that snapshot under Conditions when this happened.

It is the difference between guessing and knowing. A misfire recorded at 2,800 rpm under load on a warm engine is a different fault from one recorded at idle from cold, even though both store P0301. Read this before you buy any parts.

Generic OBD-II stores one freeze frame, for the fault that turned the warning light on, so not every code in a list has one.

Description, causes and steps

Description is the longer explanation: what the system does and what going wrong looks like.

Potential causes is ranked by how often each one is actually the answer, not alphabetically and not by cost. The order is the useful part.

Troubleshooting steps is where to start, in sequence. Each step is chosen to rule something out, so working down the list narrows the problem instead of shuffling it.

Component names the part of the vehicle involved, which helps when the code language is abstract.

Other manufacturers’ meanings

Some codes mean different things on different makes. Where that is true, the app shows what the code means elsewhere, clearly marked as other manufacturers, and Applies to names the makes the main definition covers.

This exists because a search engine will happily hand you a Ford answer for a Toyota code. The app tells you which one you are reading.

At the foot is Source: SAE J2012, the standard the generic definitions come from.

Reading further

Our code library has longer write-ups for the codes people hit most, with the diagnostic sequence set out at more length than fits on a phone screen. The guides cover whole systems rather than single codes, which is often what you actually need: a P0420 is rarely a conversation about one part.

Explain in depth

At the foot of the screen is Explain in depth, which is the AI analysis. It cross-references the code against your specific vehicle, the other codes stored and your live data, and sorts its answer into what is most likely, what is probably not it, and what to check next. Each check is tagged DIY or Workshop.

This is the one paid feature in the app. Chapter twelve covers it.

What to do next

Chapter seven is clearing codes, and the one trap that catches people every time.