You have driven normally, perhaps for several days, yet an OBD scanner still reports one or more monitors as Not Ready. This does not tell you which component, if any, is faulty. It tells you that the vehicle has not reported the required completed self-test in the observation window that the scanner is displaying. 1
There is no universal number of miles that guarantees all readiness monitors will complete. Different systems use different conditions; some require specific operating circumstances or may be prevented by an issue that needs diagnosis. An arbitrary 'just drive 100 miles more' recommendation may waste time or overlook useful evidence. 1
What to Check Before Another Trip
First confirm the scanner is showing since DTCs were cleared status. Some devices can also show monitor status for the current drive cycle, and those are not interchangeable. Next check whether the MIL is commanded on and whether you have actually read confirmed and pending DTCs. Note whether a battery disconnection, repair or code clear happened before the first incomplete reading. 1 2
If several monitors are incomplete just after a confirmed reset, a reset-related explanation is plausible. If one monitor persists across repeated comparable readings with no known reset, that is useful information to bring to a technician. Neither pattern proves a specific mechanical cause. 1 1
Keep a Before-and-After Record
Our free log is designed for this exact problem. Enter today's statuses as they appear on the scanner, including Not Supported and Unknown. Save that reading with the date, observations and recent events. After a later scan, add another reading under the same diagnostic horizon. The tool will highlight supported monitors that changed from incomplete to complete and any contradictions worth checking. It will not turn an unexpected return to Not Ready into a false 'part failure' alert.
Record your scanner observations.
When to Seek More Specific Information
If an active MIL or confirmed fault code is present, address that evidence first. If monitors remain incomplete despite attempts to follow verified manufacturer conditions, request the exact OEM information for your engine/calibration or have a qualified diagnostic technician evaluate the case. Do not repeatedly erase codes to clear an inspection failure: it can reset monitor states and destroy useful evidence. 1 1
Never try unsafe acceleration, braking or speed-holding maneuvers based on a generic web list. Manufacturer test procedures are vehicle-specific; use ordinary safe operation and appropriate professional guidance.
Common Questions
Can a monitor be incomplete without the Check Engine Light on? Yes; readiness and MIL are different observations. Check both. Does Not Ready mean the emissions component failed? No, not from this status alone. Can I compare two screenshots from different scanners? You can record them, but differences in source, reporting window or vehicle support may make the comparison inconclusive.
Related: EVAP not ready → Read the guide; trouble codes and readiness → Read the guide; inspection limits → Read the guide.
Sources & limits
These references support general explanations, not a verified drive cycle for your vehicle. Check inspection requirements with your current official program.