Readiness monitors are self-tests the ECU runs to verify emissions systems are working. After a battery disconnect or a code clear, these reset to “Not Ready” and must complete before most inspection programs will pass your vehicle.
• Continuous monitors: Misfire, Fuel System, Comprehensive Components — run all the time.
• Non‑continuous monitors: Catalyst, O2 Sensor, O2 Sensor Heater, EVAP, EGR/Secondary Air, Heated Catalyst — need specific conditions (drive cycle) to complete.
Inspection programs read these flags to ensure your vehicle has self‑tested properly. Too many “Not Ready” statuses means an automatic fail even if no codes are present.
Each manufacturer has exact steps, but a generalized sequence helps many vehicles complete monitors:
1) Cold start and idle 2–3 minutes (A/C off, electrical loads minimal).
2) Steady cruise 40–55 mph for 5–10 minutes.
3) Decelerate without braking (closed throttle) to ~20 mph.
4) Vary speeds between city (25–35 mph) and highway (55–65 mph) for 10–20 minutes.
5) Park, key off, and allow a full cool‑down for EVAP tests if needed.
• Fault codes are still present or intermittent (pending/permanent).
• Fuel level outside required range (often 15%–85%) for EVAP.
• Coolant temperature never reaches normal operating range (thermostat/stats stuck open).
• Vehicle never experiences steady cruise or closed‑throttle decel conditions.
• Recently cleared codes; some monitors need multiple trips.
Most OBD‑II scanners show an “I/M Readiness” screen. Look for each monitor’s status (Ready / Not Ready / Unsupported). Unsupported monitors don’t count against you for inspections.
• Learn to read codes: How to Read Codes on Your Car.
• Understand OBD‑II basics: OBD‑II Beginner’s Guide.
• Need a better scanner for readiness? How to Choose an OBD‑II Scanner.
How many monitors can be Not Ready and still pass? It depends on your state; some allow one or two Not Ready monitors on 2001+ vehicles. Check your local rules.
Does clearing codes fail inspection? Clearing resets monitors, which likely causes a fail until monitors complete again.
Do I have to do the exact factory drive cycle? It helps, but many vehicles set with varied normal driving over a few days.
