Readiness assistant

After clearing trouble codes, replacing the battery or a repair, the emission system’s self-tests (readiness tests, monitors) are reset and only run again during suitable drives. The readiness assistant shows which tests are still incomplete, which of them already finished during the current drive, and what kind of drive typically completes the rest.

obd-diag readiness --port /dev/ttyUSB0
obd-diag readiness --demo           # sample vehicle, no car needed
obd-diag readiness --port /dev/ttyUSB0 --json

In the graphical interface the assistant sits in the Readiness tab below the monitors. After “Connect & scan” it shows a driving hint for every incomplete test; the button Read status of this drive additionally asks for the status of the current drive without repeating the whole diagnosis.

Two states: since clearing and during this drive

Request	Meaning	reset
Mode 01 PID 01	status since the trouble codes were cleared	when clearing (Mode 04)
Mode 01 PID 41	status during this drive cycle	every time the ignition is switched on

PID 41 reports three states per test: complete, incomplete (the test may run but has not finished) and suspended (the conditions to start it were not met during this drive, e.g. temperature or fuel level). Because the status of this drive starts over at the next start, check it at the end of a drive with the engine running. If the vehicle does not report PID 41, the assistant only shows the status since clearing.

Driving hints

The hints describe typical drives per test, separately for petrol and diesel engines, for example for the exhaust gas sensor on a diesel: about 20 minutes at a steady speed on country roads or the motorway with a hot exhaust system, with overrun phases in between (lift off the accelerator without braking). These are rules of thumb, not a standard: SAE J1979 only defines how the status is reported. When a test runs is up to each manufacturer, and it often takes several drives, including a cold start after the car has stood for several hours. If trouble codes are stored, some tests only run once the cause is fixed.

As with readiness itself: this is not an emissions test verdict. An official emissions test always includes a tailpipe measurement.

What is sent

Only read requests: initialise the adapter, negotiate the protocol (0100), then 0101 and 0141. Both are listed in the Command reference; the answer layout is in OBD-II services. In demo mode (Try it without a car) the exhaust gas sensor is incomplete and not yet complete during this drive; the answer to 0141 there is an invented sample value because it was not recorded on the real car.