Readiness sets an OBD monitor to "ready" when it cannot complete on its own, usually because its system is disabled in the same file. Only the self-test report changes: emissions, fault codes and the warning lamp stay as they were. For tuners and workshops: send the file with a request, we check the ECU and return a file with corrected checksums, on average within 30–60 minutes.
What OBD readiness monitors are
Apart from the fault memory, the ECU keeps a separate list of self-tests called monitors. Each one checks its own system: the catalyst, the oxygen sensors, the evaporative system (EVAP), EGR, the particulate filter. A scan tool reads their status in the OBD section as Mode 1 PID 01. The same reply shows whether the MIL is on and how many confirmed codes are stored.
A monitor has three states. Complete means the test has run since the last reset, not that the system is healthy: a test that found a fault has also run, and its result is a stored code. Incomplete means the test has not run yet, even on a car in perfect order. Not supported means the car never had that system.
Apart from the continuous ones, monitors only run under the right driving conditions, which is why they sit at "Not Ready" after a reset.
Why monitors show Not Ready after clearing codes or flashing
Readiness is counted from the moment the ECU last cleared its diagnostic memory. Anything that clears that memory also resets readiness:
- clearing codes with a scan tool, including after flashing a file;
- writing a file to the ECU, as a rule, whether it is a software update or a tune;
- disconnecting, draining or replacing the battery, on many cars.
On a healthy car this sorts itself out. California's CARB suggests driving as usual for about a week, and the Ohio EPA mentions two or three days of city and highway driving. The flip side is that an active fault stops some monitors from running at all. Toyota lists an unlit MIL as a precondition for its EVAP test, and VW requires no stored faults in the ECU before its readiness drive.
How long to drive before the monitors are ready
Each monitor has its own requirements. Some examples from manufacturer documentation:
| Monitor | What it needs (example) |
|---|---|
| Misfire | VW TDI: restart the engine and let it idle for 45 seconds |
| Oxygen sensors | Honda: warm engine, about 3.5 miles and a deceleration with the throttle fully closed |
| Catalyst | Honda: about 5 miles of stop-and-go driving with periods of steady cruise |
| EGR | Honda: about 1 mile with a warm engine. VW TDI: about a minute with exhaust above 300 °C and no coasting, 20 seconds steady in 3rd gear at 1800 rpm, then 8 seconds of coasting |
| EVAP | Toyota Prius: an 8-hour soak, or until coolant and intake air are within 7 °C of each other, both between 4.4 and 35 °C, MIL off; then about 15 minutes at 80–104 km/h (50–65 mph) |
| PM filter, NMHC catalyst | VW TDI: build up soot and complete a regeneration |
| NOx / SCR | VW TDI: 30–40 minutes at a steady 80–120 km/h (50–70 mph) in 5th or 6th gear, longer in winter |
The full VW TDI procedure takes 60–90 minutes of driving, and VW's bulletin on these diesels states that incomplete readiness does not point to a technical problem.
After flashing any file, be it Stage 1 or a return to stock, open the readiness screen and tell the owner that "Not Ready" is normal and the monitors will set with driving. Avoid clearing codes for no reason: VW advises resetting the ECU only when a code is stored and the MIL is on, otherwise the whole cycle starts over.
When a monitor will never become ready
Driving fixes it
- codes cleared, battery disconnected, file flashed
- short trips, frost or heat: the monitor lacks its conditions
- the particulate filter has not reached a regeneration yet
Driving does not fix it
- the MIL is on or a fault is stored: repair it first
- the component is removed or disabled in software, so there is nothing to test
- the sensor the monitor relies on is disabled, such as the rear oxygen sensor for the catalyst
On the same VW TDI, the PM filter and NMHC catalyst monitors complete through a regeneration. After DPF OFF the ECU no longer starts regenerations, so both monitors stay incomplete. Something similar can happen to EGR after EGR OFF and to the catalyst after CAT/LAMBDA OFF, depending on how that ECU implements the monitor.
What the Readiness option changes
The file changes how the ECU reports readiness for monitors whose systems are disabled: instead of a permanent "Not Ready" they show as complete. The method depends on the ECU family. The option usually goes into the same file as the system disable itself.
| Item | Stock | With Readiness |
|---|---|---|
| Monitor of the disabled system | incomplete, the test never finishes | shown as complete |
| Other monitors | set by driving | same as stock |
| Fault codes and MIL | set by real faults | unchanged |
| Actual emissions | as they are | unchanged |
The option repairs nothing, does not turn off the MIL and does not put removed parts back. At a roadworthiness test in the EU, missing factory emission control equipment is a reason for failure in itself under Directive 2014/45/EU. In Germany a tailpipe measurement has again been mandatory in the emissions test since 2018, and monitor readiness has no effect on that result. Individual faults unrelated to the disabled system are handled with DTC OFF.
How to order
- Read the original file with the tool you normally use, over OBD or on the bench.
- Upload it to the portal, select READINESS and list the monitors in the comment. If a system is disabled in the same file, add that option to the order.
- Wait for our reply: solutions are ECU-specific, so we check the file and tell you whether one exists for yours. The finished file with corrected checksums takes 30–60 minutes on average.
- Flash the file and check the readiness screen: the remaining monitors will set with driving.
The Readiness option does not make a vehicle compliant with emission standards: actual emissions, fault codes and the condition of its systems stay exactly as they are. Using it to pass a roadworthiness or emissions inspection that the car would otherwise fail is cheating the inspection, and it is illegal. Disabling emission systems on public roads is prohibited in the EU, the UK, the US and many other countries. The service is intended for professionals and applies where the law permits it: motorsport, off-road use, vehicles not used on public roads. Responsibility for using the file lies with the vehicle owner.
Send the file with a READINESS request: we will check the ECU, and the finished file arrives in 30–60 minutes on average.
Order ReadinessFrequently asked questions
What are OBD readiness monitors?
They record whether the ECU has run the self-test of each emission system since the last reset: catalyst, oxygen sensors, EVAP, EGR, particulate filter. Complete means the test has run, not that the system is healthy: the result shows up as fault codes.
Why are the monitors Not Ready after clearing codes or flashing?
Readiness is counted from the moment the diagnostic memory was cleared. Clearing codes, flashing a file and, on many cars, disconnecting the battery reset it, and the monitors have to set again through driving.
How long do I need to drive to set the monitors?
On a healthy car, usually two or three days to about a week of normal city and highway driving. EVAP, which needs a long cold soak, and the particulate filter, which needs a regeneration, tend to take longest.
Do I need the Readiness option after Stage 1?
No, if all systems are fitted and working: after flashing, the monitors will set on their own. The option is only for the monitor of a system disabled in the file.
Why does a monitor stay incomplete even though the car is driven every day?
Most often an active fault or a lit MIL is blocking it, because some monitors will not run while it is present. Other causes are monitors with special conditions, such as EVAP, or a component or sensor that is removed or disabled in software.
Will Readiness turn off the check engine light?
No. The option only changes the readiness report; fault codes and the MIL work as before. Faults unrelated to the disabled system are handled with DTC OFF.
Can I pass an inspection with the Readiness option?
The option does not make the car compliant, and using it to pass an inspection the car would otherwise fail is illegal. Besides, in the EU missing factory emission equipment is a reason for failure in itself, and in Germany the emissions test measures gases at the tailpipe.
Which ECUs is the Readiness option available for?
The solution is matched to the specific ECU. Send the file with a request and we will check whether there is a solution for yours; the finished file arrives in 30–60 minutes on average.