Not ready?
Start with
what you know.

Your scan tool says EVAP Not Ready, Catalyst Incomplete, or something similar. You may have just changed a battery, cleared a check-engine code, or driven for days without seeing a monitor finish. The useful question is not simply how to force a monitor to Ready; it is what your readings actually establish and which information you should check next. 1 1 1

Start with the reading, not a guess. Our free OBD Readiness Troubleshooter helps you record the statuses your scan tool or inspection report provides. Enter the supported monitors, Check Engine Light status, any diagnostic codes you have checked, and relevant recent events. It then explains what is observed, what remains uncertain, and the next reasonable data checks. You can add another reading later to see what changed and print a summary for a mechanic. It does not connect to your car or magically determine whether a part has failed.

What Does Not Ready Mean?

An OBD readiness monitor is a built-in emissions-related self-test. When a supported monitor reads Not Ready, its required self-test has not completed in the relevant observation window. That can happen after a code clear or battery disconnection, but it can also reflect test-enabling conditions that have not occurred or another issue that needs professional attention. A missing test result does not establish that an EVAP valve, oxygen sensor, or catalytic converter is defective. 1 1 1

Ready means a supported monitor reported completion at the time of the scan. Not Supported means the monitor is not applicable or is not reported as supported by the vehicle's system; it is not another way of saying Not Ready. Unknown means you do not yet have enough trustworthy information. Our tool keeps all four states distinct rather than converting blanks into failures.

What You Need to Use the Tool

You can begin with the I/M readiness section of an OBD-II scan tool or an inspection report. Ideally, note whether its readings are since DTCs were cleared or for the current driving cycle; those windows must not be mixed. Also record whether the ECU commands the MIL on, whether confirmed/pending codes were checked, and whether the battery was disconnected or codes were cleared recently. If you don't know an answer, select Unknown. 2

The site does not require your VIN, an account or a subscription. You can keep your case privately on your device, update it after your next scan and export it. No server-side diagnostic records are needed.

How the Results Work

The assistant does not rank random repairs. It first checks urgent warnings, then active MIL or known trouble-code information, missing scan context, recent reset events and incomplete-monitor patterns. Next checks are provided as a short list of evidence-gathering steps, not as guaranteed repair instructions. If an OEM-specific drive cycle is required, the assistant tells you that a year/make/model alone may not establish the correct procedure and points you toward the manufacturer's documentation. 1

If your Check Engine Light is flashing or your vehicle exhibits serious symptoms, do not attempt a drive cycle based on a website; arrange appropriate professional help. If you simply want to know the legal emissions-test result, consult your current local program. Rules and vehicle exceptions are not uniform across the US. 3 4

Get Started

Record your scanner observations.

Additional guides

• Monitors still incomplete after ordinary driving → Read the guide
• Readiness after a battery change → Read the guide
• Trouble codes vs readiness → Read the guide
• What Ready / Not Ready / Not Supported mean → Read the guide

This is an informational tool, not a professional repair diagnosis or a smog-test certificate. The explanations on this page draw on official OBD readiness guidance and manufacturer-specific examples. References are listed below.