OBD2 Readiness Monitors Explained (2022)

OBD2 Readiness Monitors are simple yet powerful self check routines. They provide insight to the car’s self-diagnostics. This tutorial will explain in detail what the readiness monitors are.

The purpose of readiness monitors is to self-test the car’s emission control systems. The monitors are also known as Emissions Monitors. Like the name indicates, they observe the performance of car’s emission related systems.

Cars may perform up to 11 system tests or routines. These tests are so called readiness monitors. The output of readiness monitors tell you whether the car’s computer has completed the tests successfully.

Readiness Monitor types

There are two different types of readiness monitors: continuous and non-continuous. Continuous monitors are different in design from the non-continuous ones. Continuous monitors are being constantly tested and evaluated while the engine is running. The non-continuous monitors need certain conditions to be met before a test can be completed.

The conditions necessary to run the non-continuous self-diagnostic tests vary. Some monitors require that the car follows a predefined drive cycle routine. Some require two drive cycles because of the need for a cool down and warm up periods between. Each emission monitor can have different requirements for the conditions.

Previously, the OBD2 standard (SAE J1979) categorized each defined monitor as either one. In the latest standard edition, this definite allocation is no longer present for all of them. Thus, OBD Auto Doctor doesn’t follow the categorization anymore either.

(Video) Emissions Test - What are I/M Readiness Monitors And How To Fix

Continuous or Non-continuous Monitors

These monitors can be of either type. It’s up to the manufacturer to decide.

  • Misfire
  • Fuel System
  • Comprehensive Component

Non-Continuous Monitors

Non-continuous monitors are different for spark ignition cars (gasoline engines) and compression ignition cars (diesel engines).

Spark ignition vehicles (Gas)
  • Catalyst (CAT)
  • Heated Catalyst
  • Evaporative (EVAP) System
  • Secondary Air System
  • Oxygen (O2) Sensor
  • Oxygen Sensor Heater
  • EGR (Exhaust Gas Recirculation) and/or VVT System
Compression ignition vehicles (Diesel)
  • NMHC Catalyst
  • NOx/SCR Aftertreatment
  • Boost Pressure
  • Exhaust Gas Sensor
  • PM Filter
  • EGR and/or VVT System
OBD2 Readiness Monitors Explained (1)

Monitoring cycles

Traditionally, the only monitor status was the status since the diagnostic trouble codes were cleared. This readiness monitor status is mandatory for all OBD2 compliant vehicles. It will show the long term status after the check engine light was reset and the DTCs cleared.

As the OBD2 has evolved, newer vehicles can now report emission monitor status also for the current driving cycle. These monitors start from the beginning every time when the monitoring cycle begins. Older cars might not support this feature. In that case, OBD Auto Doctor will mark it as NA or Not Available.

Monitor status

Readiness monitor test result yields the monitor status. Each readiness monitor will have its own output status. The completion status can be:

  • Complete or ready meaning that the test has been completed. It means that the OBD-II system has checked this emissions control system and it has passed the test. OBD Auto Doctor indicates this by green check mark.

  • Incomplete or not ready meaning the test is not completed. It means that the OBD2 system has not been able to run this routine or it has failed. OBD Auto Doctor indicates this by red exclamation mark.

    (Video) How to Check Readiness Monitors - Emission Inspection

  • Disabled meaning that the test has been disabled for the rest of this monitoring cycle. A monitor can be disabled when there is no easy way for the driver to operate the vehicle to allow the monitor to run. For example, the ambient air temperature might be too low or too high.

OBD Auto Doctor lists all the defined monitors in the software. But the actual status can be reported only for the ones that the car supports too. It is not required for a car to support all the monitors. NA or not available monitor means that the car doesn’t have that monitor. Thus it can’t be tested.

OBD2 Readiness Monitors Explained (2)

Why is a monitor incomplete or “not ready”

Clearing the diagnostic trouble codes (DTCs) and the Check Engine Light will reset the monitor statuses too. This typically occurs during or after vehicle repair.

Statuses are also reset in case of power failure. This usually happens when the battery has been disconnected. That’s why it is not advisable to disconnect the battery. If you need to disconnect the battery for example to replace it, read further. You will learn how to get the monitors back to complete.

For the current monitoring cycle, or “this drive cycle”, the status is set to incomplete upon starting a new monitoring cycle. It is a normal situation for these monitors to be incomplete when starting the engine.

Depending on your country and state, OBDII vehicle may not pass the annual inspection unless the required monitors since reset are complete. For example, the US Environmental Protection Agency guidelines allow up to two monitors to be not ready for model year 1996 through 2000 vehicles. For 2001 and newer model year vehicles only single monitor status can be incomplete or not ready.

How to get the monitors complete or “ready”?

Because the monitors are self check routines, the best way to get them ready is to drive the car. Yet, monotonic driving will not most likely meet all the needed conditions. That’s why there is so called OBD drive cycle. But before going into that, let’s go through the obvious ones.

(Video) OBDII Readiness Monitors Overview

  1. First, make sure that the MIL (Malfunction Indicator Light) is not commanded on. Having stored or even pending diagnostic trouble codes active may prevent a monitor from running to completion.

  2. Second, make sure that you have enough fuel in the car. Some monitors, for instance the EVAP monitor, may require the fuel level to be between 35% and 85% to initiate the diagnostic testing.

  3. Third, complete the so called “drive cycle”. About one week of combined city and highway driving is usually enough to allow the monitors to reach complete status. The drive cycle is explained in more details in the next paragraph.

OBD drive cycle

The purpose of the OBD2 drive cycle is to let your car run on-board diagnostics. This, in turn, allows the readiness monitors to operate. And detect potential malfunctions of your car’s emission system. The correct drive cycle for your car can vary greatly depending on the car model and manufacturer. Also, the monitor in question affects the required drive cycle.

Today, many vehicle manufacturers include these drive cycles in the vehicle owner’s manual. Typically, a few days of normal driving, both city and highway, will make the monitors ready. The following generic drive cycle can be used as a guideline if a specific drive cycle is not known. It will assist with resetting monitors when a car specific drive cycle is not available. However, it may not work for all cars and monitors.

The drive cycle can be difficult to follow exactly under normal driving conditions. Thus, it is better to drive it in restricted area!

  1. The universal OBD-II drive cycle begins with a cold start. You should have coolant temperature below 50 C/122 F, and the coolant and air temperatures within 11 degrees of one another. This condition can be achieved by letting the car to sit overnight.

    (Video) What are emissions readiness monitors anyways?? and...car repair verification using fuel trim data

  2. The ignition key must not be left ON position before the cold start. Otherwise the heated oxygen sensor diagnostic may not run.

  3. Start the engine and idle the engine in drive for two and half minutes, with the A/C and rear defroster on if equipped.

  4. Turn the A/C and rear defroster off, and speed up to 90 km/h (55 mph) under moderate, constant acceleration. Hold at a steady speed for three minutes.

  5. Slow down to 30 km/h (20 mph) without braking. Do not depress the clutch if you are running with manual transmission.

  6. Speed up back to 90-100 km/h (55-60 mph) at 3/4 throttle. Hold at a steady speed for five minutes.

  7. Slow down to a stop without braking.

Get ready for inspection

To avoid rejection in the annual inspection, you can prepare your car for the check yourself. You should at least read the readiness monitors and make sure they are ready. This will save you from almost guaranteed rejection.

(Video) Checking OBD 2 Readiness Monitors I/M

You should also read the diagnostic trouble codes and make sure there are none present. You can do all this with OBD Auto Doctor diagnostic software. You can read the monitor statuses and the diagnostic trouble codes even with the free version. So why not try the software right now?

And remember, do not wait until the annual inspection with the issues. Acting immediately could save you a lot of time as well as future repair and fuel costs.

Editor's note: This tutorial has been updated in March 2020 for accuracy and the latest information.

FAQs

How do I know when my drive cycle is complete? ›

15 minutes of steady driving on an expressway/highway followed by 20 minutes of stop-and-go driving with at least four 30-second idle periods. Allow the vehicle to sit for at least eight hours without starting the engine. Then, start the engine and complete the above driving cycle.

How do you read OBD readiness? ›

To check if the readiness codes are set, turn the ignition switch to the ON (II) position, without starting the engine. The MIL will come on for 20 seconds. If it then goes off, the readiness monitors are set. If it blinks five times, the readiness monitors are not set.

How many monitors should be ready? ›

How Many Monitors Have to be Ready? The US Environmental Protection Agency (EPA) guidelines allow up to two monitors to be in a "not ready" state for model year 1996 through 2000 vehicles and one monitor "not ready" for 2001 or newer model year vehicles.

How long do I have to drive my car to reset the computer? ›

The readiness monitors will remain until the car has been driven long enough for the computer to evaluate the various system and sensors. The amount of time can vary based on the vehicle. In some cases it can take up to 100 miles for all of the computer monitors to completely reset.

How many miles does it take to reset readiness monitors? ›

The standard is 50-100 miles, but you can determine what is best for your car based on many factors. Driving will allow the car computer to monitor the situation and determine if the check engine light is still necessary for you to see.

How many miles do you have to drive after resetting? ›

So why is the light still on? Here's something you probably don't know: after clearing the car's computer you will need to drive for about 50 to 100 miles. As you drive your car the computer will monitor all the sensors and register the results.

How long should your test drive be? ›

You should drive all of the vehicles you're considering on the same day so that you can compare them more easily. Drive them as long as possible—at least 30 minutes—and over different types of road surfaces and in various driving conditions. Plan your own driving route in advance.

How many miles do you have to drive a car after you reset the check engine light? ›

How Many Miles to Drive after Resetting Check Engine Light for Inspection. You have to drive about 50 to 100 miles on average to clear a check engine light.

How long does it take to complete a drive cycle? ›

How Long does it Take to Complete a Drive Cycle. Preparation for it will take eight hours but, all in all, a basic drive cycle test should take around 30 minutes to complete, with about 20 minutes of actual driving. Understanding your vehicle's overall health can help you ensure it drives smooth and lasts long.

What are normal obd2 readings? ›

The normal MAP sensor reading is 29.6-inches hg at sea level if the engine is not running and around 9.6-inches hg at idling speed. The reading will rise to as high as 29.6-inches at wide open or full throttle.

What does incomplete readiness monitors mean? ›

A readiness monitor that is 'not ready' or 'incomplete' warns a potential buyer of several possible issues including problems with the system in question, an erased computer memory, recent repairs that may have caused the memory to be erased, or the vehicle's battery may have recently gone dead.

Can you pass emissions with one monitor not ready? ›

Assuming your vehicle is gasoline powered, it can be administered the California emissions inspection and pass the smog test even if one (1) incomplete monitor exisits.

Are 2 monitors enough? ›

A survey of over 1,000 end users found an average productivity increase of 42% when users worked with two monitors instead of one. Some other advantages that the study mentioned include: Two monitors often cost less than one large one. Two displays can offer better resolution than one large screen.

Is it better to have 3 monitors or 2? ›

Three monitors will provide a more immersive experience over a dual monitor setup, though the latter is no slouch in that department either. This increased immersion can be helpful while playing computer games, editing videos, or even watching movies or TV shows.

Will touching battery cables together to reset computer? ›

How To Reboot Your Car ~ Battery VooDoo - YouTube

Does disconnecting car battery reset computer? ›

A. It depends on the car's age and type of ECU used. On some older cars, disconnecting the battery will reset the system but in most new cars it does nothing, except potentially reset the clock and radio station presets.

How long does battery need to be disconnected to reset ECU? ›

You should leave your car's battery disconnected for a minimum of fifteen minutes and no longer than thirty minutes to reset an ECU. To disconnect a car battery, remove the negative power cable from the negative terminal of your car battery with the use of a socket or monkey wrench.

How do you complete a drive cycle for smog in less than 30 minutes? ›

how to complete a drive cycle for smog in less than 30 minutes

How can I turn off my check engine light to pass emissions? ›

Tricks to Use to Pass an Emissions Test Every time - How to ... - YouTube

Does clearing codes reset readiness? ›

Clearing the codes will completely reset your readiness flags. It will take a few drive cycles before you would be able to pass an OBDII emissions inspection.

How do you complete a drive cycle without driving? ›

start the vehicle and let it idle for two to three minutes in park or neutral. while it is idling, turn on the head lights, heater/defroster, and rear defroster for a three to five minute warm-up phase. let the idle speed settle down to near the normal speed.

Does an engine rebuild reset mileage? ›

Does Rebuilding an Engine Reset the Mileage? With regard to whether or not a new engine will reset the odometer, the answer is simple: no. This is because both the engine and the odometer are two separate mechanisms in your car.

Does replacing the odometer reset mileage? ›

Even though many people believe that putting a brand new engine resets mileage, it is just a misconception. The odometer counts the mileage of the car as a whole and not for the specific parts.

Can you drive too slow in a test? ›

You might be driving slowly to ensure that you pass your test, but this is misguided, since where you drive hesitantly your examiner will see a lack of skill. Believe it or not, slow driving is likely to be marked as a fail-worthy driving fault, in the same category as stalling the engine or mounting the pavement.

How fast should I drive during my test? ›

Drive at a Speed That's Safe for the Conditions

If there is traffic or bad weather, slow down a bit. In normal conditions, maintain a speed that is within three- to five-miles-per-hour of the limit and you should be fine. One word of caution - don't go too slow either. You can actually fail due to driving too slowly.

What questions should you ask when test driving a car? ›

6 Questions to Ask During a Test Drive
  • Is there visibility? How well you can see out of a vehicle is paramount to your safety. ...
  • Does it fit my needs? ...
  • Is it intuitive? ...
  • How does it perform? ...
  • Is it easy to park? ...
  • Does it have any deal breakers?

How do I reset my catalytic converter? ›

7 Steps to Follow When Catalyst Monitor Not Ready
  1. Make Sure the Engine Light is Off. ...
  2. Check if your Vehicle has a Coolant Temperature. ...
  3. Let the Engine be Idle for 2 Minutes. ...
  4. Drive the vehicle at a Steady Speed of 55 MPH. ...
  5. Decelerate your Vehicle's Speed at 20 MPH. ...
  6. Again Speed Up. ...
  7. Stop the Vehicle.
5 Sept 2018

How many drive cycles are there? ›

There are two types of driving cycles: Transient driving cycles involve many changes, representing the constant speed changes typical of on-road driving. Modal driving cycles involve protracted periods at constant speeds.

How do I fix OBD monitor not ready? ›

Start the engine and let it idle in Drive for about 2 ½ minutes with the air conditioning and rear defroster on. Turn the air conditioning and rear defroster off. Drive the vehicle for 10 minutes at highway speeds. Drive the vehicle for 20 minutes in stop-and-go traffic.

Does engine need to be running for OBD2? ›

But do you need to run your car's engine before you have access to the diagnostic system? The quick answer is no; you only need to turn on the ignition, so there is power available for the scanner.

How accurate are OBD2 readers? ›

Entirely accurate. These devices are not rocket science, and nor are they pocket mechanics. They simply report out the codes they extract from the car's computers.

Can I use OBD2 while car is running? ›

It's completely safe to leave an OBD2 scanner tool plugged in while driving. In fact, it's important to have your car running while you diagnose an engine code to avoid damaging the scanning software.

Can you pass emissions with catalyst not ready? ›

Answer: Depending how old your vehicle is, the catalyst monitor might be allowed to remain incomplete and the vehicle still pass the smog inspection. Currently 1999 and older gasoline powered vehicle's are allowed one incomplete monitor.

Why is my Catalyst monitor Not ready? ›

if the oxygen sensor and catalyst monitors are also not ready, the culprit is most likely a weak battery. if your battery is more than four years old, replace it and re-run the drive cycle. even though your car may start just fine, the pcm is hypersensitive to the slightest glitch in the battery.

How do I fix incomplete catalyst monitor? ›

How to Fix Catalyst Monitor Incomplete?
  1. Ensure The Engine Warning Light is Off.
  2. Verify That The Coolant Temperature Remains Normal.
  3. Let The Engine Run Idle for Two Minutes.
  4. Operate The Car At A Constant 55 Mph.
  5. Reduce Your vehicle's Speed by 20 miles Per Hour.
  6. Continue Accelerating.
  7. Stop the Automobile.
9 Jun 2022

Can you pass emissions with stored codes? ›

Answer provided by. Yes, a car should still pass emissions with a pending code. There is a difference between pending codes and hard codes. Pending codes mean that there may be a problem and your vehicle's computer needs to run more diagnostics.

How many monitors do you need to pass smog? ›

If more than two monitors are incomplete the vehicle will fail the smog inspection. Some vehicles are known to have difficulties completing OBD II monitors and may be subject to different rules.

Can you pass emissions with an engine light? ›

A vehicle will not pass an emissions test when the check engine light is on.

Do I need 2 monitors to code? ›

It is a common misconception that one monitor is not enough for coding. In reality, it can be very efficient. Although, a lot of people have been using multiple monitors for years now. However, if you're a developer who really codes, there are some great benefits to using just one monitor for coding and development.

Is it better to have 1 monitor or 2 monitors? ›

The verdict is clear. In general, dual monitors take the win over ultrawide. Going dual snags you a more flexible setup that's better for multitasking and, if you buy high-end 4K monitors, packs more pixels than any ultrawide in existence.

How many monitors should I use? ›

Triple monitor setups are great for boosting productivity and saving time. According to a study of computers, using three monitors at work can boost workers' productivity by up to 35%.

Why do people buy 2 monitors? ›

Dual monitors make collaboration between employees easier than ever. You can communicate with team members on one screen while working on a project on the other one. Having a second monitor gives you a lot of additional space to collaborate with the rest of the organization.

Why would you need more than 1 monitor? ›

Using a second monitor makes it far easier and faster to use multiple programs simultaneously. Instead of having to switch between full-screen windows, the second program can be put on the second monitor, making for fewer clicks and faster workflow.

Why do people need more than 2 monitors? ›

Benefits of Dual Monitors

A dual monitor setup makes it possible for you to enjoy multitasking while playing your favorite video games. This extra screen real estate can be used as a desktop for web browsing, watching videos, or for displaying walkthroughs and other information for a game.

How do I clear my evap readiness monitor? ›

Start the engine and idle for four minutes, then drive in stop-and-go traffic for five minutes using smooth accelerations and decelerations. Stop and idle for 4 minutes. The EVAP monitor should be complete.

How do you complete a drive cycle without driving? ›

start the vehicle and let it idle for two to three minutes in park or neutral. while it is idling, turn on the head lights, heater/defroster, and rear defroster for a three to five minute warm-up phase. let the idle speed settle down to near the normal speed.

How do I get my catalytic converter monitor ready? ›

7 Steps to Follow When Catalyst Monitor Not Ready
  1. Make Sure the Engine Light is Off. ...
  2. Check if your Vehicle has a Coolant Temperature. ...
  3. Let the Engine be Idle for 2 Minutes. ...
  4. Drive the vehicle at a Steady Speed of 55 MPH. ...
  5. Decelerate your Vehicle's Speed at 20 MPH. ...
  6. Again Speed Up. ...
  7. Stop the Vehicle.
5 Sept 2018

How do I fix OBD monitor not ready? ›

Start the engine and let it idle in Drive for about 2 ½ minutes with the air conditioning and rear defroster on. Turn the air conditioning and rear defroster off. Drive the vehicle for 10 minutes at highway speeds. Drive the vehicle for 20 minutes in stop-and-go traffic.

Can I pass emissions with EVAP not ready? ›

Gasoline Vehicles:

- 2000 and newer model year vehicles will need all emission monitors in READY or COMPLETE status, with the exception of the EVAP monitor. AN incomplete evaporative monitor will not cause a smog check failure.

Can you pass emissions with one monitor not ready? ›

For 2000 and newer cars, the United States EPA allows one monitor to be in a not ready state. 2000 and newer gas vehicles must have ALL monitors in a ready state with the exception of the EVAP monitor.

Does clearing codes reset readiness? ›

Clearing the codes will completely reset your readiness flags. It will take a few drive cycles before you would be able to pass an OBDII emissions inspection.

How many miles do you have to drive after resetting? ›

So why is the light still on? Here's something you probably don't know: after clearing the car's computer you will need to drive for about 50 to 100 miles. As you drive your car the computer will monitor all the sensors and register the results.

How many miles do you have to drive after disconnecting battery? ›

WAIT A BIT AFTER DISCONNECTING THE BATTERY

When a car's battery dies or is disconnected, the computer resets, erasing the internal emission monitors required to pass a smog test. You'll be good to go once you drive 100 to 200 miles with the new battery.

How long does it take for a car computer to cycle? ›

How Long does it Take to Complete a Drive Cycle. Preparation for it will take eight hours but, all in all, a basic drive cycle test should take around 30 minutes to complete, with about 20 minutes of actual driving. Understanding your vehicle's overall health can help you ensure it drives smooth and lasts long.

At what temperature does a catalytic converter start working? ›

CONVERTER OPERATION

The average light off temperature at which a catalytic converter begins to function ranges from 400 to 600 degrees F. The normal operating temperature can range up to 1,200 to 1,600 degrees F. But as the amount of pollutants in the exhaust go up, so does the converter's operating temperature.

How do you tell if your catalytic converters are clogged? ›

Among the symptoms of a bad catalytic converter are:
  1. Sluggish engine performance.
  2. Reduced acceleration.
  3. Dark exhaust smoke.
  4. The smell of sulfur or rotten eggs from the exhaust.
  5. Excessive heat under the vehicle.
24 Jan 2016

How do I check if my catalytic converter is clogged? ›

TEST YOUR CATALYTIC CONVERTER IN 15 MINUTES!

What does incomplete readiness monitors mean? ›

A readiness monitor that is 'not ready' or 'incomplete' warns a potential buyer of several possible issues including problems with the system in question, an erased computer memory, recent repairs that may have caused the memory to be erased, or the vehicle's battery may have recently gone dead.

What causes catalyst not ready? ›

if the oxygen sensor and catalyst monitors are also not ready, the culprit is most likely a weak battery. if your battery is more than four years old, replace it and re-run the drive cycle. even though your car may start just fine, the pcm is hypersensitive to the slightest glitch in the battery.

Can AutoZone check OBD readiness? ›

We can help you get a reading yourself. Borrow an OBD reader to get a Check Engine Light reading with the AutoZone Free Fix Finder Service. It's a simple task that takes less than two minutes.

Videos

1. how to complete a drive cycle for smog in less than 30 minutes
(Cooking with Dr. Chill)
2. Smog Check Fail OBDII Monitor Not Ready 236 Miles Drive Cycle Episode 1
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3. Toyota Matrix and Pontiac Vibe Drive cycles and emission readiness monitors explained
(Electricaljunky)
4. Evap Monitor Not Ready? Pass Smog Evaporative Emission Control System Monitor Explained
(RANDOMFIX)
5. The Trainer #62: How To Master Your Global OBD II Scan Tool - The First 5 Modes Of OBD II
(Motor Age)
6. Honda OBD II Emission Monitor Status - Readiness Code Checking Using the Instrument Cluster
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