Car OBDII Monitor Driving: Understanding Readiness for Vehicle Inspections

Ensuring your vehicle is environmentally compliant is crucial, and OBDII readiness monitors are at the heart of this process. These self-diagnostic routines are integral to your car’s emission control system, offering valuable insights into its health. As an expert from autelfrance.com, I’m here to provide a comprehensive guide on Car Obdii Monitor Driving, explaining what these monitors are, why they matter, and how to ensure they are ready for your vehicle inspection.

OBDII readiness monitors, also known as emissions monitors, are essentially self-tests that your car’s computer performs on its emission control systems. Their primary purpose is to verify that these systems are functioning correctly and minimizing harmful pollutants. Think of them as vigilant observers, constantly assessing the performance of your car’s emission-related components while you drive.

Modern vehicles can conduct up to 11 different system tests, each represented by a readiness monitor. The result of these monitors indicates whether your car’s onboard computer has successfully completed these tests. A “ready” status signifies that the emission system in question has passed its self-diagnostic check.

Decoding Readiness Monitor Types: Continuous and Non-Continuous

OBDII monitors are broadly categorized 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 for systems that require ongoing evaluation. The key 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 system to ensure the correct air-fuel mixture for optimal combustion and emission control.
• Comprehensive Component Monitor: Oversees a wide array of engine and emission-related components for proper function.

Non-Continuous Monitors: Unlike their continuous counterparts, non-continuous monitors require specific driving conditions to be met before they can execute their self-tests. These conditions are often referred to as “enable criteria” and can vary significantly depending on the monitor and vehicle manufacturer. Some monitors might need a predefined driving pattern, known as a drive cycle, to become ready. Others may require multiple drive cycles, incorporating cool-down and warm-up periods.

It’s important to note that while older OBDII standards categorized monitors definitively as continuous or non-continuous, the latest standards offer more flexibility to manufacturers. Therefore, a specific monitor’s type can vary between vehicle makes and models.

Non-Continuous Monitor Examples

The specific non-continuous monitors present in your vehicle depend on whether it’s a spark ignition (gasoline) or compression ignition (diesel) engine.

Spark Ignition Vehicles (Gasoline Engines):

• Catalyst (CAT) Monitor: Evaluates the efficiency of the catalytic converter in reducing harmful emissions.
• Heated Catalyst Monitor: For vehicles with heated catalytic converters, this monitor checks the heater functionality to ensure rapid catalyst activation.
• Evaporative (EVAP) System Monitor: Tests the integrity of the fuel vapor recovery system to prevent fuel vapors from escaping into the atmosphere.
• Secondary Air System Monitor: If equipped, this monitor verifies the operation of the secondary air injection system, which assists in reducing emissions during cold starts.
• Oxygen (O2) Sensor Monitor: Assesses the performance of the oxygen sensors, crucial for maintaining the correct air-fuel ratio.
• Oxygen Sensor Heater Monitor: Checks the functionality of the oxygen sensor heaters, ensuring they reach operating temperature quickly for accurate readings.
• EGR (Exhaust Gas Recirculation) and/or VVT System Monitor: Monitors the Exhaust Gas Recirculation (EGR) system, which reduces NOx emissions, and Variable Valve Timing (VVT) systems, which can improve efficiency and reduce emissions.

Compression Ignition Vehicles (Diesel Engines):

• NMHC Catalyst Monitor: Evaluates the Non-Methane Hydrocarbon (NMHC) catalyst used in diesel engines to reduce hydrocarbon emissions.
• NOx/SCR Aftertreatment Monitor: Monitors the NOx reduction system, often Selective Catalytic Reduction (SCR), which is crucial for diesel emission control.
• Boost Pressure Monitor: Checks the boost pressure system in turbocharged diesel engines, which affects engine performance and emissions.
• Exhaust Gas Sensor Monitor: Monitors various exhaust gas sensors specific to diesel engines, such as NOx sensors or particulate matter sensors.
• PM Filter Monitor: Evaluates the performance of the Particulate Matter (PM) filter or Diesel Particulate Filter (DPF) in trapping soot particles.
• EGR and/or VVT System Monitor: Similar to gasoline engines, monitors the EGR and/or VVT systems for emission control and efficiency.

Image: OBDII readiness monitors displayed on a Windows computer screen using diagnostic software.

Monitoring Cycles: Since Reset and This Drive Cycle

Traditionally, OBDII systems primarily reported monitor status since the last time diagnostic trouble codes were cleared. This “since reset” status is mandatory for all OBDII compliant vehicles and provides a long-term overview of emission system performance after any resets or repairs.

However, modern vehicles often offer an additional feature: monitoring status for the current driving cycle. These monitors initiate testing at the beginning of each new driving cycle (when the engine is started). This allows for a more immediate assessment of system readiness. Older cars might not support this “this drive cycle” feature, in which case diagnostic tools will typically indicate “NA” or “Not Available.”

Understanding OBDII Monitor Status: Complete, Incomplete, and Disabled

Each OBDII readiness monitor reports a specific status, indicating the outcome of its self-test. The possible statuses are:

• Complete (Ready): A “complete” or “ready” status signifies that the monitor has successfully run its diagnostic test and the emission control system has passed. This is the desired status for vehicle inspections. Diagnostic tools often represent this with a green check mark.
• Incomplete (Not Ready): An “incomplete” or “not ready” status means that the monitor has not yet completed its self-test. This could be because the necessary driving conditions haven’t been met, or the test has failed. This status is often indicated by a red exclamation mark.
• Disabled: A “disabled” status indicates that the monitor has been temporarily deactivated for the current monitoring cycle. This can occur when specific conditions prevent the monitor from running, such as extreme ambient temperatures that are outside the monitor’s operational parameters.
• Not Available (NA): “Not Available” means that the vehicle does not support a particular monitor. It’s not mandatory for all vehicles to support every defined OBDII monitor.

Image: OBDII readiness monitors shown on an Android app, indicating “Not Available” for “this drive cycle” monitors.

Why is an OBDII Monitor Incomplete or “Not Ready”?

There are several common reasons why an OBDII monitor might show an “incomplete” or “not ready” status:

• Recent Diagnostic Trouble Code (DTC) Clearing: Clearing DTCs, which often happens when the check engine light is reset or after vehicle repairs, also resets the readiness monitor statuses.
• Battery Disconnection: Power loss, such as disconnecting the car battery, will also reset monitor statuses. This is why disconnecting the battery unnecessarily is generally discouraged, especially before a vehicle inspection.
• New Monitoring Cycle: For “this drive cycle” monitors, it’s normal for them to initially be incomplete when the engine is first started, as they begin their testing process anew.
• Driving Conditions Not Met: Non-continuous monitors require specific driving conditions to run. If these conditions haven’t been encountered during your driving, the monitors will remain incomplete.

It’s crucial to understand that depending on your location’s emission testing regulations, your vehicle might fail its annual inspection if the required monitors are not in a “complete” state. For instance, in the United States, EPA guidelines permit a limited number of “not ready” monitors for vehicles to pass inspection, with stricter limits for newer models.

How to Drive to Get OBDII Monitors Complete or “Ready”

The most effective way to set OBDII readiness monitors to “complete” is by driving your vehicle under conditions that allow the monitors to run their self-tests. While simply driving around will eventually set many monitors, a more structured approach, known as an OBDII drive cycle, can expedite the process.

Before initiating a drive cycle, ensure the following:

1. No Active MIL (Malfunction Indicator Light): Make sure the check engine light is not illuminated. Active or even pending DTCs can prevent monitors from completing.
2. Adequate Fuel Level: Some monitors, particularly the EVAP monitor, require the fuel tank to be between 35% and 85% full to initiate testing.
3. Consider a Generic Drive Cycle: If you are unsure of your vehicle’s specific drive cycle, a generic OBDII drive cycle can often be effective. Combined city and highway driving over about a week can also be sufficient for most monitors to become ready under normal circumstances.

The Generic OBDII Drive Cycle Procedure

The following generic OBDII drive cycle is a guideline that can help reset monitors when a vehicle-specific drive cycle isn’t available. However, it may not work for all vehicles and monitors, and it’s crucial to perform it safely and legally, ideally in a controlled or restricted area due to the driving maneuvers involved.

1. 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.
2. Ignition Key Position: Ensure the ignition key is not left in the “ON” position before the cold start, as this can interfere with heated oxygen sensor diagnostics.
3. Idle in Drive (2.5 minutes): Start the engine and idle in drive for two and a half minutes. Engage the A/C and rear defroster if equipped to increase engine load.
4. 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 constant speed for three minutes.
5. Deceleration (No Braking): Slow down to 30 km/h (20 mph) without using the brakes. If driving a manual transmission, do not depress the clutch.
6. 3/4 Throttle Acceleration and Steady Speed (5 minutes): Accelerate back up to 90-100 km/h (55-60 mph) using approximately 3/4 throttle. Hold this steady speed for five minutes.
7. Controlled Stop (No Braking): Decelerate and come to a complete stop without using the brakes.

Preparing for Your Vehicle Emission Inspection

To avoid failing your vehicle’s annual emission inspection, proactive preparation is essential. Before your inspection, it’s highly recommended to check your OBDII readiness monitors to ensure they are “ready.” This simple step can prevent a likely rejection.

Furthermore, it’s wise to read your diagnostic trouble codes to confirm there are no active DTCs present. You can easily accomplish both of these tasks using OBD Auto Doctor diagnostic software. Even the free version of the software allows you to read monitor statuses and DTCs, making it a valuable tool for vehicle owners. Try the software right now and gain peace of mind before your inspection.

Remember, addressing potential emission issues promptly, rather than waiting for the annual inspection, can save you significant time, prevent future repairs, and even improve fuel economy.

Editor’s note: This article was updated in March 2020 to ensure accuracy and reflect the latest information on OBDII readiness monitors and drive cycles.