OBD2 Readiness Monitors: What They Are (Inspection/MOT)
Table of contents
Key Takeaway
Need to pass an emissions inspection? You must understand readiness monitors first.
OBD2 readiness monitors are self-tests your car runs to verify each emissions subsystem is functioning. They must be "complete" before an emissions inspection — most inspection programs fail vehicles with more than 1-2 incomplete monitors. Clearing codes or disconnecting the battery resets all monitors, requiring 50-100 miles of mixed driving to complete again. STEER displays each monitor's current status live.
What Are Readiness Monitors?
Readiness monitors are self-tests the vehicle runs to verify that emissions systems are working. They must be "complete" (or "ready") to pass an emissions inspection. For complete code references, see our [OBD-II codes pillar](/codes/).
The Monitors
| Monitor | What It Tests | Type |
|---|---|---|
| Catalyst | Catalytic converter efficiency | Continuous |
| Heated Catalyst | Heated cat warmup | Continuous |
| EVAP | Fuel vapor system integrity | Non-continuous |
| Secondary Air | Secondary air injection | Non-continuous |
| Oxygen Sensor | O2 sensor response | Non-continuous |
| O2 Heater | O2 sensor heater function | Non-continuous |
| EGR | Exhaust gas recirculation | Non-continuous |
| Misfire | Engine misfire detection | Continuous |
| Fuel System | Fuel delivery control | Continuous |
Why Monitors Reset
Clearing codes (Mode 04) or disconnecting the battery resets all monitors to "not ready." They need 50-100 miles of varied driving to complete again.
How to Complete Monitors
Drive a mix of city and highway for 50-100 miles. Include cold starts, steady highway cruising, and stop-and-go city driving. Most monitors complete within 2-3 drive cycles.
STEER tracks monitor completion live
Driving 100 miles hoping you've completed enough monitors to pass inspection is a frustrating gamble. The [STEER OBD-II adapter](/obd2-scanner/) shows each monitor's current status — Ready or Not Ready — in the app, so you know exactly when to schedule re-inspection. No paying for a re-test only to fail again.
Frequently Asked Questions
How many readiness monitors can be "Not Ready" and still pass inspection?
Most US OBD-II testing states allow up to 2 incomplete monitors for 2000+ model year vehicles and 1 incomplete monitor for 1996-1999 vehicles. Specific rules vary by state — check your DMV or emissions inspection program. The catalyst and EVAP monitors are usually allowed to be incomplete because they are the slowest to set; the misfire, fuel system, and comprehensive monitors are continuous and must be ready.
How do I complete OBD2 readiness monitors quickly?
Follow the manufacturer's drive cycle when available, or a standard pattern: cold start (engine below 122°F), 4-5 minutes of city driving, 5-10 minutes of highway cruise at steady speed, 30 seconds of idle, deceleration coast, and another idle period. EVAP and catalyst monitors require partial fuel level (15-85% tank) and stable ambient temperature. Total time: 100-200 miles of mixed driving for full completion.
Why are my readiness monitors not ready after I drove 100 miles?
Some monitors require specific operating conditions that may not occur in routine driving. EVAP needs cool engine + partial fuel + stable temperature. Catalyst needs sustained mid-load cruise. EGR needs specific load/RPM windows. If you only drive short trips, certain monitors may never complete. Try a single longer highway drive with at least one cold start and varied speed.
Can I cheat readiness monitors before an emissions test?
No — and attempting to is a federal Clean Air Act violation. Tools that claim to "force" monitors to Ready usually just write false PIDs that inspection programs detect and flag. Some shops offer to mask incomplete monitors, but the inspection software cross-checks against actual monitor history and flags inconsistencies. The legitimate path is to fix the underlying fault, clear the code, and drive enough miles for monitors to complete naturally.
Get plain-English answers on your iPhone
STEER reads your car's codes the moment they trigger and translates them into something you can act on.
Related reads
Keep going. These pair well with what you just read.
- OBD-II
OBD-II Codes Explained: A Complete Guide
A complete breakdown of OBD-II diagnostic trouble codes. Learn what P0, C0, B0, and U0 codes mean and how to read them.
14 min read - OBD-II
Where Is the OBD-II Port in My Car?
Can't find the OBD-II port? Here's exactly where to look, what it looks like, and what you can do with it.
5 min read - OBD-II
Best OBD-II Scanners 2026: Buyer's Guide
The complete buyer's guide to OBD-II scanners in 2026. Compare types, features, and prices to find the right one for you.
10 min read - OBD-II
Bluetooth OBD2 Scanner — Authoritative Buyer's Guide (2026)
BLE vs Classic Bluetooth, iPhone vs Android, $10 dongle vs $100 premium. Here is the honest buyer's guide that explains every tradeoff before you click "Add to Cart."
13 min read