Readiness Monitors and Smog Checks: Will Your Car Pass?

Last updated October 28, 2026 · By OBD Scanner Guide Editorial Team

A smog check on a 1996 or newer car is mostly a computer check: the station plugs into the OBD2 port and asks whether the check engine light is commanded on and whether the car’s self-tests, called readiness monitors, have finished. The short answer on whether you will pass: if the light is off and no more than one monitor is incomplete on a 2001 or newer car (two on a 1996 to 2000 car), most programs that follow the federal procedure will pass it. California is stricter, and some states differ, so check before you go. A basic scanner with an I/M readiness function tells you in about a minute. This is an editorial guide based on federal and state program pages and published product specs; no testing was done.

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What readiness monitors are

The OBD2 system runs self-tests on emission-related systems. Some run all the time; others only run under specific conditions, such as after a cold start, during steady cruising or with a certain fuel level. Each monitor reports “complete” (ready) or “incomplete” (not ready). Not ready does not mean failed; it means the test has not finished since the last reset.

Not every car has every monitor; a scanner shows “N/A” for ones your car does not support. The continuous and non-continuous split above follows the ANCEL AD310 manual’s description, which is typical of how scanners present it.

The pass rules, by program

The federal OBD inspection procedure, 40 CFR 85.2222, lets model year 1996 to 2000 vehicles pass with two or fewer unset monitors and 2001 and newer vehicles with no more than one. A check engine light commanded on is a fail. Codes stored without the light commanded on are not a fail under that procedure, and a light that does not come on at key-on with the engine off is also a fail.

States run their own programs on top of that:

As of October 2026. California’s Bureau of Automotive Repair says new regulations from October 1, 2025 require all monitors that can feasibly set to be set, but its readiness rules explainer says pass/fail criteria stay as above while BAR collects data, and any change will be announced in advance. Other states set their own rules; check your program’s page before you test.

Why monitors reset to not ready

The Texas DPS readiness FAQ calls disconnecting the battery the most common cause, and lists the usual reasons it happens: tune-ups and engine repairs, a dead battery replacement, and radio or alarm installs. Clearing trouble codes with a scan tool does the same thing. New York’s DMV adds two less obvious ones: an engine computer that needs a software update, and a pending problem that has not lit the check engine light yet.

That last one matters. If a monitor refuses to complete after a week of normal driving, the car may be detecting a marginal fault each time the test runs and not finishing it. Check for pending codes.

How to check readiness before you go

1. With the engine off, plug the scanner into the OBD2 port under the dash.
2. Turn the ignition on (or start the engine, as the tool directs).
3. Open the I/M readiness function. Note each monitor as complete, incomplete or not supported.
4. Read stored and pending codes while you are connected.
5. Compare the count of incomplete monitors with your state’s allowance for your model year.

If you see one incomplete monitor on a 2001 or newer car in a state that follows the federal allowance, you are likely fine. If you are in California with a 2000 or newer gas car, anything other than EVAP incomplete is a problem.

How to use an OBD2 scanner walks through connecting, reading codes and saving freeze frame in the right order.

If you want a dedicated readiness light, the FOXWELL NT301 has an I/M hot key with red, yellow and green LEDs and a speaker, per Foxwell. On a phone, BlueDriver lists a Smog Check feature that reads the monitors. Best OBD2 scanner compares them.

How to get monitors to complete

There is no universal drive cycle, because each carmaker sets its own enabling conditions. In order of preference:

1. Use your vehicle’s drive cycle. Check the owner’s manual (New York DMV suggests looking under “OBD”) or service information. California BAR’s OBD Test Reference lists drive cycles for vehicles known to be hard to set.
2. Drive normally for several days. Include an overnight cold start, some idling, steady highway cruising and stop-and-go driving.
3. Try a generic cycle. The New York DMV’s not-ready brochure publishes one: from a cold start idle in drive for 2.5 minutes with the A/C and rear defroster on; turn them off, accelerate to 55 mph and hold for 3 minutes; coast down to 20 mph without braking; accelerate to 55 to 60 mph and hold for 5 minutes; coast to a stop. It suggests a half to three-quarters tank of fuel and says most cars need two cycles with a cool-down between. It also notes the generic cycle will not work on every vehicle and that you must obey traffic laws. Only do the highway portions where the speed is legal and safe.

Fuel level matters for EVAP: many EVAP monitors only run within a band of tank fill, which is why the half-to-three-quarters advice exists.

If you fail as not ready

• New York: if not-ready monitors are the only reason and your inspection has expired, the station can issue a 10-day extension to finish the drive cycle; a re-inspection fee may apply, per NY DMV.
• California: the Smog Check Referee can help vehicles that have trouble meeting the readiness requirements, per BAR.
• Everywhere: check for pending codes, ask whether a software update applies, and confirm the monitor completes on your own scanner before paying for another test.

Code-specific readiness traps

Mistakes to avoid

• Clearing codes the morning of the test. It guarantees not-ready monitors.
• Disconnecting the battery to “reset the computer”. Same result.
• Assuming California follows the federal one-monitor rule. For 2000 and newer gas cars it does not.
• Reading readiness with a dealer tool in enhanced mode. Texas DPS notes it must be in generic OBD2 mode to show readiness.
• Driving a generic drive cycle unsafely. Speeds and coasting steps only where legal and safe.

Verdict

Before any OBD smog check, spend a minute with a scanner: light off, no stored codes, and incomplete monitors within your state’s allowance for your model year. If monitors are incomplete after a repair or a battery change, drive through a real mix of conditions for several days, follow your vehicle’s drive cycle if one exists, and only go back once the scanner says ready.