Readiness monitors and emissions tests

Open Readiness from the Home screen. This is the screen to check before an inspection, and almost nobody knows it exists.

What a monitor is

Your engine computer runs a set of self tests on the emissions equipment. Each test is a monitor, and each has a name: catalyst, evaporative system, oxygen sensor, oxygen sensor heater, exhaust gas recirculation, and others depending on the vehicle.

Each one is either complete, meaning it has run since the last memory wipe and has a result, or not ready, meaning it has not run yet.

An emissions station checks that the light is off, that no codes are stored, and that the monitors have run. A car that is mechanically perfect but has just had its codes cleared fails on the third one.

The verdict at the top

The screen leads with the answer: Ready for an emissions test or Not ready yet. Everything below explains it.

Since codes cleared

This is the section that matters for an inspection. It lists every monitor with one of three states.

Ready means the test has run and has a result.

Not ready means it has not run since the last time the computer’s memory was cleared.

Not supported means your vehicle does not have that system. A car with no secondary air injection reports that monitor as not supported permanently, and that is correct, not a problem.

This drive cycle

Some vehicles also report how the monitors are doing on the current trip, with Complete, Not yet and Not this cycle. Where your car reports it, the app shows it as a second section.

It is useful for watching progress in real time. It is not what an inspection reads.

Getting the monitors to run

They reset themselves, through driving. There is no button, no tool and no shortcut that does it.

What they need is variety: a cold start after the car has sat overnight, some steady highway cruising, some stop-and-go, and then leaving it alone again. Commonly 50 to 100 miles of mixed driving, though it depends on the vehicle. Driving the same four miles to work twice a day can take a fortnight.

The evaporative monitor is the stubborn one. On many vehicles it will only run with the fuel level between roughly a quarter and three quarters of a tank, at a particular ambient temperature range, after a long enough soak. It is often the last one to go green.

Most tests allow one incomplete monitor

Inspection rules vary by jurisdiction, and many allow one incomplete monitor on a newer vehicle and two on an older one. The evaporative monitor is frequently the one permitted to be incomplete, precisely because it is so hard to run.

So Not ready yet on this screen does not automatically mean a fail. One amber monitor out of eight is often fine. Six are not.

Saving it for the station

The printer icon on this screen produces a readiness report you can show, print or email. The screen also re-reads itself every fifteen seconds while it is open, so you can watch a monitor flip on a drive.

What to do next

Chapter nine is live data, which is what the car is doing right now rather than what it remembers.