Readiness monitors are the self-tests your car's computer runs on its emissions systems, like the catalytic converter, oxygen sensors, and EVAP system. Each monitor reports ready once it completes its check. Smog stations look at these to make sure the systems have been verified before passing your vehicle.
Animated: how a Emissions Readiness Monitors actually works
🔧 How It Works, Step by Step
1
Systems are checked
The computer runs separate tests for the converter, O2 sensors, EVAP, and more.
2
Conditions must be met
Each monitor needs specific drive conditions like warm-up, cruising, or idle.
3
Monitor runs
When the right conditions occur, the test runs and evaluates the system.
4
Status set to ready
A passing test flips the monitor from not ready to ready.
5
Inspection reads status
A smog check confirms enough monitors are ready before passing the car.
🧩 The Key Parts
Onboard diagnostics
Runs and stores the results of each emissions self-test.
Drive cycle logic
Defines the conditions each monitor needs to run.
Readiness flags
Record whether each monitor is complete.
OBD-II port
Lets a scanner or smog station read the monitor status.
📋 Free OBD2 Code Cheat Sheet
The 50 most common check engine codes with likely cause and DIY fix cost. Sent once.
🩺 Signs of a Failing Emissions Readiness Monitors
Monitors not ready at a smog check
Failed inspection due to incomplete monitors
Recent battery disconnect or code clearing
Check engine light preventing readiness
Scanner shows monitors incomplete
Repeated failed drive cycles
⚠️ Common Problems
Reset monitors
Clearing codes or disconnecting the battery resets all monitors to not ready.
Incomplete drive cycle
Not driving the required mix of conditions leaves monitors unset.
Active fault
An unresolved emissions fault stops a monitor from ever completing.
❓ FAQ
How do I set my readiness monitors?
Drive a normal mix of city and highway conditions over several days after codes clear. A specific drive cycle for your car sets them fastest.
Can I pass a smog check with monitors not ready?
Most states allow only one or two incomplete monitors. Too many not ready will fail the inspection until you drive to set them.
Why did my monitors reset?
Disconnecting the battery or clearing trouble codes wipes the stored results, so the monitors must run again to become ready.