Reading trouble codes

The Codes tab is the heart of the app. One scan reads all three kinds of trouble code from every module that answers, and groups them.

Confirmed codes

A confirmed code is a fault the engine computer has seen often enough to be sure about. This is the group that turns your check engine light on, and the group to work through first.

Pending codes

A pending code is a fault seen once, which the computer is waiting to see again before it commits. Most emissions faults have to happen on two separate drives before the light comes on, and a pending code is the state in between.

Pending codes are genuinely useful. They are early warning. A pending P0420 weeks before the light comes on is time to work out whether it is the catalytic converter or an oxygen sensor lying about it, rather than a surprise the week of an inspection.

A pending code that does not recur clears itself. That is the system working.

Permanent codes

A permanent code is a confirmed fault that the vehicle will not let you erase. Clearing codes with any tool leaves it in place, and it stays until the car has re-run the relevant self test and satisfied itself the fault is actually gone.

This exists specifically to stop someone clearing codes in the car park outside an emissions station. You cannot work around it, and neither can we.

Codes stored with the light off

If the app lists codes and your dashboard light is off, nothing is broken. It happens for several ordinary reasons: the codes are pending rather than confirmed, the fault was intermittent and the light self-extinguished after enough clean drives, or the codes are in a module whose faults do not light that particular lamp.

The app puts a banner at the top of the Codes tab when it spots this, so the mismatch is explained rather than left to worry you.

Severity

Each code carries a severity: low, medium or high. Treat it as a rough sort order for where to start, not a verdict. A high severity misfire like P0301 is genuinely worth stopping for. A low severity evaporative code like P0455 usually means a loose gas cap and can wait until the weekend.

Severity is about what the fault can do to the vehicle, not about what the repair costs.

Rescanning

The refresh icon at the top, tooltip Rescan, reads the car again. Pull down on the list to do the same thing. Use it after clearing codes, after a repair, or after driving a while to see whether a pending code has firmed up.

When descriptions do not appear

The codes themselves come from your car and always work. The plain English explanations come from us and need an internet connection.

With no signal you still get every code number, grouped correctly, with a banner reading Descriptions need an internet connection. Tap Retry descriptions once you have signal back and the explanations fill in without rescanning the car. This matters more than it sounds: plenty of breakdowns happen where there is no coverage, and a code number you can write down is better than an error screen.

Reading the whole scan at once

The printer icon at the top left produces a report of the entire scan, which you can preview, print, share or email. Chapter eleven covers reports.

What to do next

Tap any code to open it. Chapter six is what that screen tells you.