The Home screen and your vehicle

The app has four tabs along the bottom: Home, Codes, Live and Settings. Home is where it lands once you connect, and it is designed to answer the only question most people arrived with.

The vehicle header

At the top sits what the app has worked out about the car it is plugged into. It reads your VIN from the engine computer and decodes it, so you should see a make, model and year rather than a serial number.

Some vehicles do not publish a VIN. On those you get a year and a region instead, which is what the app could safely determine, and everything else in the app works exactly the same.

Tapping the header opens the Vehicle screen, covered below.

The status card

The large card underneath is the answer. It reads one of four ways.

No trouble codes means the engine computer reports no stored faults. If your check engine light is off, that is the whole story.

Trouble codes found with a count means there are stored faults but the warning light is not on. This is normal and chapter five explains why.

Check engine light is on means both: the light is lit and there are codes behind it.

Couldn't read trouble codes means the scan did not finish. Tap it to try again.

Tapping the card takes you to the Codes tab either way.

Scan codes

The blue Scan codes button re-reads the car from scratch. The app scans when it connects, so the button is for after you have changed something: cleared a code, tightened a gas cap, replaced a sensor, driven a while.

Pull down on the screen to refresh everything at once, which re-reads the VIN, the vehicle details, the codes and the readiness monitors together.

The four tiles

Below the status card are four checks, each with its own screen.

Readiness is emissions monitor status, and chapter eight covers it. Underneath the tile the app prints how many monitors are ready, because that is the number that decides whether a test station passes you.

Fuel trim measures how hard the engine is working to correct its own fuel mixture.

Battery check reads charging voltage.

Acceleration times a run. All three are in chapter ten.

The Vehicle screen

Tapping the vehicle header opens a screen with everything the car will tell you about itself, in three groups.

Identity is the VIN, the model year and what the app decoded from it: model, series, check digit, manufacturer.

Engine & drivetrain is the engine, cylinder count, displacement and drive type, where the VIN encodes them.

Provenance is where the vehicle was assembled.

Underneath those is Safety recalls, which is the one thing on that screen that does not come from your car. The app looks up open recall campaigns for your vehicle. If that lookup fails, it says so and offers Try again. It will not tell you there are no recalls when it simply could not find out, which is a distinction worth trusting.

What to do next

Chapter five is the Codes tab: the three kinds of trouble code, and why the light being off does not mean nothing is stored.