EVAP Monitor Not Ready: Meaning, Causes, and Fixes

If your scan tool displays “EVAP Monitor Not Ready,” you may wonder what could be wrong with your car’s system. In this article, I will discuss what “EVAP System Monitor Incomplete” means and why it does not automatically mean that your car’s system is faulty.

EVAP System Monitor Incomplete: What it means

The Evaporative Emission Control System (EVAP) system is a crucial system. It monitors fuel vapor leaks and prevents fuel vapor from polluting the atmosphere. “EVAP Monitor Not Ready” is more or less saying your vehicle doesn’t detect fuel vapor because the EVAP monitor is not ready for a self-test. If it detects such a problem, the monitor activates the MIL immediately. Then, the OBD scanner displays the information.

There are specific driving and engine conditions that should be met for the proper running of the EVAP monitor. The EVAP monitor will not function if you do not meet those conditions, starting from the previous time you:

  1. Cleared all DTCs from the Power Control Module memory
  2. Disconnected or replaced your battery
  3. Ran your monitor

In EVAP system monitoring, the charcoal canister stores the fuel vapor and prevents it from polluting the atmosphere. When the engine is on, the PCM unlocks the purge valve. This allows the intake vacuum to extract the vapors from the canister into the engine. 

If the PCM does not detect airflow when the engine is on, and the purge valve is opened, it triggers the MIL. Or if it detects any leak equivalent to or higher than the required air, it will set off the check engine light.

Most Common Causes of EVAP Monitor Incomplete

  • A broken gas cap can cause leaks, affecting your car’s emissions. In effect, the EVAP monitor will not be complete.
  • If you recently reset your vehicle’s computer or changed the battery, the monitor may not be ready. It will require time under some operating conditions for the system you complete the essential checks.
  • If there are issues with the sensors controlling the EVAP system, it can cause the monitor not to be ready.
  • Faulty canister and canister purge valve. These two play a vital role in the normal functioning of the EVAP system. If faulty, they can alter the operator of the EVAP system.
  • Leaks in the system can render the monitor incomplete. The underlying problem may relate to issues with the valves, houses, and other system parts.
  • If the drive cycle of your vehicle isn’t complete, the EVAP monitor will not be complete. Granted, your vehicle can only complete the emission tests if it undergoes a full drive cycle. 

How to Get Your EVAP system Monitor Ready 

First, you may need to carry out a lot of checks on some parts in your vehicle’s system. 

  • With a scan tool, run an inspection and maintenance diagnosis to observe all monitors.
  • Check the charcoal canister, and replace it if faulty. 
  • Check the vacuum hoses. If there is any damage or a need for replacement, take action as soon as possible. 
  • Inspect the gas cap, and ensure it’s in good condition. You may as well need to tighten it if it is loose.
  • Repair or replace faulty canister purge valve.

Tips to Run a complete EVAP monitor drive cycle

As I mentioned earlier, an incomplete drive pattern may cause EVAP monitor not to be ready. So, the right thing to do is to run a complete cycle. But you must take some precautionary tips to have a successful outing.

Here are the conditions that enable you to run a complete EVAP monitor drive cycle:

  • An EVAP self-check may become inaccurate if your fuel level is extremely low. So, ensure your fuel tank is ¼ to ¾ full. 
  • Allow your vehicle to rest for up to eight hours without turning on the engine. The ambient temperature must fall between 30 and 95 degrees. 
  • Barometric pressure must be above 75 kPa. 
  • Ensure the ignition voltage is between 11 and 18 volts. 
  • To run the monitor, drive your car around for 10 minutes at 45 to 65 mph on the highway.
  • Ensure the malfunction indicator lamp (MIL) is in OFF status before starting the cycle
  • The temp values of the Intake Air temperature (IAT) sensor and engine coolant temp (ECT) sensor should be 7 degrees Celsius (45℉) and 29 degrees Celsius (85℉), respectively.
  • However, the temp value of IAT should not be -16oC (2℉) higher than ECT. Likewise, the temp value of the ECT sensor should not be -11°C (12℉) higher than the IAT sensor.
  • The throttle position sensor range should be 0.09% and 0.3%


What does “EVAP Monitor Not Ready” mean?

Your vehicle’s computer cannot perform a self-test to check the EVAP system’s functionalities.

If my EVAP monitor is not ready, can I pass an emission test?

You can pass an emission check if that’s the only unready monitor. But if other readiness monitors are also incomplete, your car will not pass an emission test until all OBD II readiness monitors are “ready.”

Read more:

Final Thoughts

The EVAP Monitor Not Ready notifies you that your precious vehicle might not pass emission checks. The reason is that the emission control system is deactivated and cannot check fuel vapor leaks. If the steps above do not resolve the issue, you may need to see a trainer mechanic for diagnosis. 

Remember that your car’s brand, model, and year will determine the number of drive cycles the system will need to run the EVAP monitor. Before you begin the drive cycle, ensure that other components in the EVAP system are operating efficiently. Clear all DTCs in consonance with the EVAP system to enable the EVAP monitor to run smoothly.

  • Eric Williams

    I'm the founder of Daily Car Tips. I wrote articles in the automotive industry for more than 10 years, published in USA and Europe. I love sharing my knowledge and insights with fellow enthusiasts. Join me on this journey as we explore the exciting world of cars together!

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