How to Get Your OBD2 Monitor Ready for Vehicle Inspection

OBD2 readiness monitors are vital self-diagnostic checks in your car that offer insights into its emission control systems. Understanding and ensuring these monitors are “ready” is crucial, especially when preparing for a vehicle inspection or addressing potential emission issues. This guide will delve into what OBD2 readiness monitors are, why they matter, and how to get them ready, ensuring your vehicle is in top shape and compliant with emission standards.

Understanding OBD2 Readiness Monitors

Readiness monitors, also known as emissions monitors, are essentially self-tests performed by your car’s onboard computer to evaluate the functionality of its emission control systems. These monitors continuously or periodically check various components and systems related to your vehicle’s emissions, ensuring they are operating correctly and minimizing harmful pollutants. Think of them as internal health checks for your car’s environmental performance.

Cars can perform up to 11 different system tests, each considered a readiness monitor. The result of these monitors – whether they are “complete” or “incomplete” – indicates if the car’s computer has successfully run and passed these self-tests. A “complete” status for all relevant monitors is generally required to pass vehicle emissions inspections in many regions.

Continuous vs. Non-Continuous Monitors

OBD2 readiness monitors are broadly classified into two types: continuous and non-continuous. This distinction lies in how and when these tests are conducted.

Continuous Monitors: These monitors operate constantly while your engine is running. They are designed to detect malfunctions in real-time. The three main continuous monitors are:

Misfire Monitor: Detects engine misfires, which can significantly increase emissions and damage the catalytic converter.
Fuel System Monitor: Checks the fuel delivery and metering system to ensure the engine is running with the correct air-fuel ratio.
Comprehensive Components Monitor: This monitor oversees a wide range of other emission-related components and sensors, ensuring they are functioning within acceptable parameters.

Non-Continuous Monitors: Unlike continuous monitors, non-continuous monitors require specific driving conditions to be met before they can run and complete their tests. These conditions, often referred to as “drive cycles,” vary depending on the monitor and vehicle manufacturer. Non-continuous monitors are further divided into categories for gasoline (spark ignition) and diesel (compression ignition) vehicles due to differences in emission control systems.

For Spark Ignition (Gasoline) Vehicles:

Catalyst (CAT) Monitor: Evaluates the efficiency of the catalytic converter in reducing harmful emissions.
Heated Catalyst Monitor: Checks the performance of heated catalytic converters, which reach optimal operating temperature faster.
Evaporative (EVAP) System Monitor: Tests the evaporative emissions control system to prevent fuel vapors from escaping into the atmosphere.
Secondary Air System Monitor: If equipped, this monitor checks the secondary air injection system, which helps reduce emissions during cold starts.
Oxygen (O2) Sensor Monitor: Monitors the performance of oxygen sensors, which are crucial for air-fuel ratio control and catalytic converter efficiency.
Oxygen Sensor Heater Monitor: Verifies the functionality of oxygen sensor heaters, ensuring sensors reach operating temperature quickly.
EGR (Exhaust Gas Recirculation) and/or VVT System Monitor: Tests the exhaust gas recirculation system and variable valve timing system, both of which help reduce NOx emissions and improve fuel efficiency.

For Compression Ignition (Diesel) Vehicles:

NMHC Catalyst Monitor: Monitors the Non-Methane Hydrocarbon catalyst, used to reduce hydrocarbon emissions in diesel engines.
NOx/SCR Aftertreatment Monitor: Evaluates the Selective Catalytic Reduction (SCR) system and other NOx reduction technologies.
Boost Pressure Monitor: Checks the boost pressure control system in turbocharged diesel engines, which affects emissions.
Exhaust Gas Sensor Monitor: Monitors various exhaust gas sensors specific to diesel engines.
PM Filter Monitor: Evaluates the Diesel Particulate Filter (DPF) system, designed to trap and remove soot from diesel exhaust.
EGR and/or VVT System Monitor: Similar to gasoline engines, this monitors the EGR and/or VVT systems for emission control and efficiency.

Understanding OBD2 Readiness Monitors Displayed on Windows Software

Monitoring Cycles: Current vs. Since Reset

Modern OBD2 systems provide two types of emission monitor status:

Status Since Diagnostic Trouble Codes Cleared: This is the traditional and mandatory status for all OBD2 compliant vehicles. It reflects the long-term status of monitors since the last time diagnostic trouble codes (DTCs) were cleared and the check engine light was reset. This is the status typically checked during vehicle inspections.
Status for the Current Driving Cycle: Newer vehicles can also report monitor status for the current driving cycle. These monitors reset and begin testing every time a new driving cycle starts (typically when the engine is started). Older cars may not support this “current drive cycle” feature. If not supported, diagnostic tools will typically indicate “NA” (Not Available).

Interpreting Monitor Status: Complete, Incomplete, and Disabled

Each readiness monitor reports one of the following statuses:

Complete (Ready): Indicated by a green check mark in many diagnostic tools, “complete” or “ready” means the monitor test has run, and the emission control system has passed the test. This is the desired status for passing emissions inspections.
Incomplete (Not Ready): Often shown with a red exclamation mark, “incomplete” or “not ready” means the monitor test has not yet been completed. This could be because the necessary driving conditions haven’t been met, the test failed, or the monitor hasn’t run since a reset.
Disabled: This status indicates that the monitor test has been temporarily disabled for the current monitoring cycle. Monitors can be disabled under certain conditions, such as extreme ambient temperatures, where it’s impractical for the driver to create the conditions needed for the test to run.
Not Available (NA): If a monitor is listed as “NA,” it means the vehicle is not equipped with that particular emission control system or monitor. It does not indicate a problem.

OBD2 Readiness Monitors Displayed on an Android App, Showing “Not Available” for Current Drive Cycle Monitors

Why Monitors are Incomplete or “Not Ready”

A common reason for “incomplete” or “not ready” monitor status is clearing diagnostic trouble codes (DTCs) and resetting the Check Engine Light. This action also resets all readiness monitor statuses to “incomplete.” This often occurs after vehicle repairs or when troubleshooting engine issues.

Disconnecting the car battery can also reset monitor statuses due to power loss to the vehicle’s computer. Therefore, it’s generally advisable to avoid disconnecting the battery unnecessarily. If battery disconnection is required (e.g., for replacement), understanding how to reset the monitors afterward is important.

For the “current monitoring cycle” status, it’s normal for monitors to be “incomplete” immediately after starting the engine, as the tests haven’t had time to run.

Crucially, many regions have regulations regarding the number of “not ready” monitors allowed for a vehicle to pass inspection. For instance, in the United States, EPA guidelines permit up to two “not ready” monitors for 1996-2000 model year vehicles and only one “not ready” monitor for 2001 and newer vehicles. Exceeding these limits will result in inspection failure.

Getting Monitors “Complete” or “Ready”: The Drive Cycle

Since readiness monitors are self-check routines, the primary way to get them ready is by driving the vehicle. However, simply driving without a plan might not fulfill all the specific conditions needed for each monitor to run. This is where the concept of an OBD drive cycle comes in.

Before initiating a drive cycle, ensure the following:

No Check Engine Light (MIL): Make sure the Malfunction Indicator Light (Check Engine Light) is not illuminated. Active or pending DTCs can prevent monitors from running to completion. Address any underlying issues causing DTCs first.
Sufficient Fuel Level: Some monitors, particularly the EVAP monitor, require the fuel level to be between 35% and 85% to initiate testing.
Understand the Drive Cycle: The specific OBD drive cycle required for your vehicle can vary significantly based on make, model, and the particular monitor in question. Consult your vehicle’s owner’s manual or repair information for the manufacturer-recommended drive cycle.

Generic OBD-II Drive Cycle (as a Guideline):

If a specific drive cycle isn’t available, a generic OBD-II drive cycle can be used as a starting point. However, it may not work for all vehicles and monitors. It’s essential to perform this drive cycle in a safe, controlled area, as it involves specific speeds and maneuvers.

Cold Start: Begin with a cold start. The coolant temperature should be below 50°C (122°F), and the coolant and air temperatures should be within 11°C (20°F) of each other. Allowing the car to sit overnight typically achieves this.
Ignition ON, Engine OFF (Briefly Avoid): Avoid leaving the ignition key in the “ON” position before the cold start, as this might prevent the heated oxygen sensor diagnostic from running.
Idle in Drive (2.5 Minutes): Start the engine and idle in “Drive” (or “1st gear” for manual transmissions) for two and a half minutes. Turn on the A/C and rear defroster (if equipped) during this step.
Moderate Acceleration and Steady Speed (3 Minutes): Turn off the A/C and rear defroster. Accelerate moderately and steadily to 90 km/h (55 mph). Maintain this speed for three minutes.
Deceleration (No Brakes, 20 mph): Slow down to 30 km/h (20 mph) without using the brakes. If driving a manual transmission, do not depress the clutch during deceleration.
Moderate Acceleration and Steady Speed (5 Minutes): Accelerate again to 90-100 km/h (55-60 mph) at approximately 3/4 throttle. Hold this steady speed for five minutes.
Controlled Stop (No Brakes): Slow down and come to a complete stop without using the brakes if possible.

Important Notes on Drive Cycles:

Safety First: Perform drive cycles in a safe and legal environment, away from regular traffic if possible.
Patience is Key: It may take multiple drive cycles and several days of combined city and highway driving for all monitors to become “ready.”
Diagnostic Tool Monitoring: Use an OBD2 scanner or diagnostic tool to check monitor status after each drive cycle segment to track progress.

Prepare for Vehicle Inspection: Check Your Monitors

Before heading to your annual vehicle inspection, proactively check your OBD2 readiness monitors. Ensuring they are “ready” beforehand can prevent a failed inspection and the inconvenience of a retest.

Utilize OBD Auto Doctor or a similar OBD2 diagnostic software or scan tool to read your readiness monitor statuses. These tools can also read diagnostic trouble codes. Address any DTCs before inspection, as their presence will also cause failure.

By taking these proactive steps and understanding how to “Get Obd2 Monitor Ready,” you can confidently approach your vehicle inspection and ensure your car is running cleanly and efficiently.