When you make purchases through links on this site, The Track Ahead may earn an affiliate commission. Also, these posts are based off my own experiences. I am not responsible for any action you take as a result of reading this. Learn More

It was time for my Acura CL-S to get a smog check, so I got my paperwork and headed to a nearby smog station. I didn’t think much of it as there wasn’t any serious issues with my car that I’d think would keep it from passing smog. I got to the smog station and the technician did a smog test; he came back to me saying that it didn’t pass smog because the OBD II monitors were not ready.

The smog tech further explained that if my battery had died recently, this would have caused the issue with the OBD II monitors being “not ready”. Whenever the battery dies, the OBD II monitors reset and you have to go through a drive cycle in order to allow these monitors to run and complete their operations. After that, I’d be able to come back to get smogged again.

So what exactly are these OBD II monitors that are “not ready” and what does it take to perform a OBD II drive cycle? I’ll dive more into the details, provide the required steps to do an OBD II drive cycle, and offer up more helpful information in this post.

What does OBD II Monitors “Not Ready” Mean?

What this means is that the on-board computer in your vehicle has not checked all of the emissions control components. Each of these components related to engine, transmission, fuel systems, and other emission controls talks with a readiness monitor. If the diagnostic data was reset (such as through a scan tool) or the battery was disconnected, then the on-board computer will report out as incomplete or not ready. If the diagnostic checks have been performed, then the computer reports out as complete.

If you’re about to get a smog test or plan to get one in the near future, and you are working on a vehicle trying to clear an engine code, it is best to make the repair and allow the on-board computer to clear the code on its own. It’s not a good idea to clear the trouble codes through a code reader because it will reset the readiness monitors. This will cause your OBD II readiness monitors to reset, causing the same issue as if your battery had died. With either scenario, you will need to perform a drive cycle before it may pass smog.

In order to get the OBD II readiness monitors to change from not ready to ready, you will need to perform a drive cycle. A drive cycle basically means running your vehicle and driving through several different conditions. Simply driving your vehicle normally over time will complete a drive cycle as you will typically encounter the conditions that would be required for a full drive cycle. However, if you need to get the OBD II monitors ready sooner, then you can perform a drive cycle to expedite this process.

How to Perform a Drive Cycle to Reset OBD II Monitors

A “drive cycle” mainly consists of four stages of operating a vehicle:

  1. Vehicle rest to get to “cold” condition
  2. Vehicle operation
  3. Higher highway speed
  4. Lower city speed

Each vehicle manufacturer may have their own specific drive cycle procedure, so you may have better luck following the specific drive cycle for your vehicle. For example, if you own a Ford you may search online: “ford how to complete drive cycle”. If you own a Toyota, search online: “toyota how to complete drive cycle”.

Some vehicles are more finicky with their drive cycles than others, but in general if you do normal driving over a period of time (200-300 miles), you will eventually complete a drive cycle. If you are in need of completing one now so that you can get your readiness monitors ready for smog, then either perform the generic drive cycle procedure below or follow a manufacturer-specific drive cycle.

Generic Drive Cycle Procedure

If you look for a generic drive cycle procedure, you will get a number of different instructions. But, in general they follow the four main stages of operating the vehicle during a drive cycle: cold vehicle, vehicle operation, higher speed, lower speed. Here is a common generic drive cycle procedure:

  1. Make sure there are no OBD II error codes on your vehicle. Use an OBD II Plug-in scan tool or a Bluetooth scan tool that communicates with your smartphone to check this.
  2. Ensure fuel tank is between 1/4 to 3/4 full.
  3. Allow vehicle to sit for at least 8 hours to ensure it is “cold”.
  4. Start vehicle to perform a “cold start”.
  5. Put in neutral or park, and idle engine for 2-3 minutes (also have rear defroster and A/C on if equipped).
  6. Turn rear defroster and A/C off, go on the highway and steadily accelerate until you reach 55 mph; then drive and maintain this speed for about 10 minutes.
  7. Exit highway and allow the vehicle to coast to slow down to a stop if possible.
  8. Drive in a City setting for about 15 minutes where you will experience stop-and-go conditions.
  9. This completes the drive cycle procedure.

Do All OBD II Readiness Monitors Need to Be Complete in Order to Pass Smog?

When I performed the drive cycle in my vehicle, I initially tried to get every one of my readiness monitors ready. The most difficult one to get into a “complete” or “ready” status was the EVAP Monitor. This is usually one of the last monitors to complete out, so I was struggling with this one. After some further research, I found that for my vehicle, I didn’t even need to have the EVAP Monitor complete in order to pass smog.

Depending on your vehicle’s model year and fuel type, you may be allowed a number of readiness monitors to be incomplete, yet still pass smog. You may reference the table below to determine whether or not you have any exceptions for passing your smog test.

Fuel TypeModel YearsNumber of Incomplete Readiness Monitors
Allowed in Order to Pass Smog Test
Gasoline1996-1999Any One
Gasoline2000 & NewerEVAP Monitor
Diesel2007 & NewerAny Two
Information from: https://www.bar.ca.gov/Industry/OBD_test_reference

How to Check OBD II Monitor Readiness by Yourself

While performing a drive cycle in an attempt to get my OBD II monitors ready, Iused an OBD II scan tool to check the readiness monitors after driving my car. I’d prefer not to go back to the smog station and find out that not all readiness monitors were ready; resulting in having to go out and perform the drive cycle all over again. Who knows how many times I’d have to do that.

A better option is to check the OBD II monitors yourself. The first OBD II scan tool I used is one of the standard handheld plugin ones that has a built-in screen to read codes. This also has the option of checking your readiness monitors. On my older code reader pictured below, determining the exact monitors and whether they were incomplete/complete is a bit difficult to do. The newer OBD II handheld code readers have better screens and readouts so that can more easily see whether or not the readiness monitors are complete.

ANCEL AD310 OBD II Scanner Car Engine Fault Code Reader

Another option for checking your readiness monitors is using an OBD II Bluetooth code reader, which allows you to connect to an app on your smartphone. I felt this was a better option for checking and testing your readiness monitors.

Veepeak BLE OBD2 Bluetooth Scanner for iOS & Android, Bluetooth 4.0

With the Bluetooth module left plugged in and your smart phone mounted, you can easily see whether or not your drive cycle was completed successfully. I used the app DashCommand, which has a lot of functionality but in this case I used it to check the readiness monitors.

There are other applications you can use, but DashCommand is a very popular one that can do other things such as monitor fuel economy, check performance, and read engine trouble codes. The last I checked, it was available for $10 on App Store for iOS (it is also available for Android as well.)

My Acura CL Type-S took quite a while to get the OBD II monitors to complete and even with all the driving I did, I still ended up with one monitor incomplete, which was the EVAP monitor. Again, since my vehicle is a gas-powered vehicle model year 2003, the EVAP monitor did not have to be completed in order to pass smog. As you can see below, it took me several drive cycles to fully complete 7 of the available readiness monitors in order to pass smog.

So using an OBD II Bluetooth code reader was ideal for my situation as it was difficult to get my readiness monitors ready and I was trying to get it complete quickly so I could pass smog. With the Bluetooth code reader plugged in, and the DashCommand app up, I could perform a drive cycle, check if the monitors were complete or not, and then continue with another drive cycle if needed. In the end, it took a few drive cycles and in total about an hour of driving time in order to get the OBD II readiness monitors ready and to successfully pass smog.




Hi there! I'm Scott and I run The Track Ahead. My goal is to provide helpful articles and tutorials based on my experience and research related to car maintenance and automotive detailing. When I'm not writing and not working my day job, you can find me spending time with my family and working on home and car projects.

Write A Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.