Emission Tests

The self-tests the ECU runs on its own, and why they matter before an inspection.

Besides the fault codes, the ECU runs self-tests on the emission systems and reports whether each one has completed. This screen shows that state.

The content has nothing to do with your country's mandatory periodic inspection or with the dealer's scheduled service. It is an internal report from the ECU about its own tests.

  1. Connect and start the engine

    Connect the adapter and start the engine. The monitors appear as the ECU runs them over the drive cycle.

  2. Read the two columns

    Status since DTC clear shows what has completed since the last time the codes were cleared. Status current drive cycle shows what has already run on this trip.

    The first column is the one that matters for an inspection; the second shows the progress right now.

  3. Interpret the results

    Each monitor appears as PASSED, NOT PASSED or N/A. The rows marked N/A are monitors your car does not implement.

    Manufacturers publish different subsets, so several rows in that state are normal and do not mean anything is wrong.

  4. Get the car ready for the inspection

    In countries where the inspection reads the OBD port, incomplete monitors fail the vehicle on their own, even with nothing wrong with it.

    The monitors complete with mixed driving, alternating town and highway, cold engine and warm engine, over a few days. There is no shortcut, which is why clearing codes shortly before an inspection is a bad idea.

If something goes wrong

It depends on the adapter being connected and on the engine running. With the ignition on alone, without starting, most ECUs do not report the monitors.

That is normal. Each manufacturer implements a different subset of the monitors the standard foresees, and a car with several N/A rows is not faulty because of it.

They depend on specific conditions and need mixed driving: stretches of town and highway, a cold start and some time at a steady speed. A short, always identical route may never complete the cycle.

That result is expected, because clearing the errors resets the monitors. They need several days of mixed driving to complete again and, over that period, the car can fail an inspection that reads the OBD port.

← All guidesIn the FAQ: Diagnostics →