OBD2 Readiness Monitors List: Your Guide to Passing Emissions Tests

Ensuring your vehicle is running efficiently and cleanly is crucial, not just for the environment, but also for your wallet and peace of mind. A key aspect of modern vehicle diagnostics is the Obd2 Readiness Monitors List. These monitors are like internal health checks for your car’s emission control systems. Understanding them is essential for anyone wanting to keep their vehicle in top condition and avoid failing emissions tests.

This guide will delve into the world of OBD2 readiness monitors, providing you with a comprehensive obd2 readiness monitors list, explaining their function, importance, and how to ensure they are “ready” for your next vehicle inspection.

Understanding OBD2 Readiness Monitors

What are OBD2 Readiness Monitors?

OBD2 readiness monitors, also known as emissions monitors, are self-diagnostic tests that your car’s onboard computer performs on its emission control systems. Think of them as a series of automated check-ups that ensure all emission-related components are functioning correctly. These monitors run in the background as you drive, constantly evaluating the performance of systems designed to reduce harmful pollutants from your vehicle’s exhaust.

Your vehicle can perform up to 11 different system tests. The obd2 readiness monitors list reflects the outcome of these tests, indicating whether each system has been successfully evaluated. A “ready” or “complete” status for these monitors is a sign that your vehicle’s emission systems are likely functioning within acceptable limits.

Why are Readiness Monitors Important?

Readiness monitors serve several critical purposes:

Emissions Testing Compliance: Most regions with vehicle emissions testing programs require a certain number of readiness monitors to be in a “ready” state for a vehicle to pass inspection. If too many monitors are “not ready,” your vehicle will likely fail, even if there are no obvious engine problems.
Early Problem Detection: Monitors can detect potential issues within your emission control systems before they become major problems or trigger the “Check Engine Light.” Addressing these issues early can prevent costly repairs and ensure your vehicle remains environmentally friendly.
Verification After Repairs: After you’ve had emission-related repairs done, readiness monitors help confirm that the repairs were successful and the systems are functioning as intended. They ensure that the underlying issue has been resolved and won’t cause future problems.

Types of OBD2 Readiness Monitors: A Detailed List

OBD2 readiness monitors are broadly categorized into two types: continuous and non-continuous.

Continuous Monitors: These monitors run constantly while the engine is operating. They are always evaluating critical emission-related components in real-time.
Non-Continuous Monitors: These monitors require specific driving conditions to be met before they can run their tests. These conditions, often referred to as a “drive cycle,” vary depending on the monitor and the vehicle manufacturer.

Here is a detailed obd2 readiness monitors list, categorized by type and vehicle type (gasoline or diesel):

Continuous Monitors

These monitors are always active when the engine is running:

Misfire Monitor: Detects engine misfires, which can significantly increase emissions and damage the catalytic converter.
Fuel System Monitor: Checks the fuel delivery system to ensure proper fuel mixture and efficient combustion.
Comprehensive Components Monitor (CCM): Oversees a wide range of engine management components and sensors for proper operation.

Non-Continuous Monitors

The obd2 readiness monitors list for non-continuous monitors differs slightly between gasoline (spark ignition) and diesel (compression ignition) vehicles due to the different emission control technologies used.

Spark Ignition Vehicles (Gas)

Catalyst Monitor (CAT): Evaluates the efficiency of the catalytic converter in reducing harmful exhaust gases.
Heated Catalyst Monitor: Specifically checks the performance of heated catalytic converters, which reach operating temperature faster for improved cold-start emissions.
Evaporative System Monitor (EVAP): Tests the fuel tank and vapor recovery system for leaks, preventing fuel vapors from escaping into the atmosphere.
Secondary Air System Monitor: (If equipped) Monitors the secondary air injection system, which helps reduce emissions during cold starts.
Oxygen Sensor Monitor (O2 Sensor): Checks the functionality of the oxygen sensors, which are crucial for air-fuel mixture control and catalytic converter efficiency.
Oxygen Sensor Heater Monitor: Evaluates the heaters for the oxygen sensors, ensuring they reach operating temperature quickly.
EGR and/or VVT System Monitor: Monitors the Exhaust Gas Recirculation (EGR) system and/or Variable Valve Timing (VVT) system, which are used to reduce NOx emissions and improve engine efficiency.

Compression Ignition Vehicles (Diesel)

NMHC Catalyst Monitor: Monitors the Non-Methane Hydrocarbon (NMHC) catalyst, used to reduce hydrocarbon emissions.
NOx/SCR Aftertreatment Monitor: Evaluates the Selective Catalytic Reduction (SCR) system, which reduces nitrogen oxide (NOx) emissions using diesel exhaust fluid (DEF).
Boost Pressure Monitor: Checks the boost pressure control system in turbocharged diesel engines.
Exhaust Gas Sensor Monitor: Monitors various exhaust gas sensors specific to diesel engines.
PM Filter Monitor: Evaluates the Diesel Particulate Filter (DPF) system, which traps and burns soot particles from diesel exhaust.
EGR and/or VVT System Monitor: Similar to gasoline engines, this monitors the EGR and/or VVT systems for emissions control and efficiency.

OBD2 Monitor Status Explained

When you check your obd2 readiness monitors list using a scan tool, you will typically see one of the following statuses for each monitor:

Complete (Ready): Indicates that the monitor has run its self-test and passed. This is the desired status for emissions testing. Diagnostic software often represents this with a green checkmark.
Incomplete (Not Ready): Means the monitor has not yet run its self-test or has not completed it successfully. This is often indicated by a red exclamation mark. A few “not ready” monitors may be acceptable for emissions testing depending on your location and vehicle year, but generally, you want as many monitors as possible to be “ready.”
Disabled: Indicates that the monitor has been temporarily disabled for the current driving cycle. This can happen due to specific environmental conditions, such as extreme temperatures, that prevent the monitor from running accurately.
Not Available (N/A): This status means that the specific monitor is not supported by your vehicle’s OBD2 system. Not all vehicles are required to support every monitor on the obd2 readiness monitors list.

Common Reasons for Incomplete Monitors

Having incomplete monitors is a common issue, and it doesn’t always mean there’s a problem with your vehicle. Here are some typical reasons why monitors might be “not ready”:

Recent DTC Clearing: When you clear diagnostic trouble codes (DTCs) or reset the “Check Engine Light,” all readiness monitors are also reset to “not ready.” This is because clearing the codes erases the history of the monitors’ test results.
Battery Disconnection: Disconnecting your car battery, even briefly, can also reset the readiness monitors. This is because the vehicle’s computer loses power and forgets the monitor status.
Drive Cycle Not Completed: Non-continuous monitors require specific driving patterns, or “drive cycles,” to run their tests. If you haven’t driven your car in a way that meets these conditions since the last reset, these monitors will remain “not ready.”

How to Complete OBD2 Readiness Monitors (Drive Cycle)

The most common way to get your obd2 readiness monitors list to show “complete” status is to drive your vehicle. However, simply driving normally might not be enough, as non-continuous monitors need specific conditions. This is where the concept of an OBD2 drive cycle comes in.

An OBD2 drive cycle is a pre-determined set of driving conditions designed to allow all non-continuous monitors to run their self-tests. The exact drive cycle can vary significantly depending on your vehicle’s make, model, and year. Some manufacturers include specific drive cycle procedures in the owner’s manual.

If you don’t have a vehicle-specific drive cycle, a generic OBD2 drive cycle can often help:

Generic OBD2 Drive Cycle Steps

Important: Perform this drive cycle in a safe and legal area, away from heavy traffic.

Cold Start: Ensure your vehicle has been sitting for several hours so the engine is completely cold. Coolant temperature should be below 122°F (50°C) and close to the ambient air temperature.
Idle: Start the engine and let it idle for 2.5 minutes with the air conditioning (A/C) and rear defroster turned ON (if equipped).
Moderate Acceleration and Steady Speed: Turn OFF the A/C and rear defroster. Accelerate smoothly and moderately to 55 mph (90 km/h) and maintain this speed for 3 minutes.
Deceleration: Slow down to 20 mph (30 km/h) without braking, if possible (allow the vehicle to coast down).
Moderate Acceleration and Steady Speed (Again): Accelerate moderately to 55-60 mph (90-100 km/h) and maintain this speed for 5 minutes.
Deceleration and Stop: Slow down and come to a complete stop without braking, if possible.

Repeating this generic drive cycle a few times, combined with regular city and highway driving over a few days, is often sufficient to set most readiness monitors to “complete.”

Readiness Monitors and Vehicle Inspection

Before taking your vehicle for an emissions inspection, it’s highly recommended to check your obd2 readiness monitors list. Using an OBD2 scan tool (even a basic one), you can quickly determine the status of your monitors.

If you find that some monitors are “not ready,” especially after recent DTC clearing or battery disconnection, performing a drive cycle can help. Allow some time for the monitors to complete their tests before your inspection appointment.

Being proactive and ensuring your monitors are “ready” can save you time, prevent inspection failures, and ensure your vehicle is running cleanly and efficiently. Consider using an OBD2 diagnostic tool to regularly check your obd2 readiness monitors list and stay informed about your vehicle’s emission system health.