Ensuring your vehicle is environmentally sound and compliant with emissions regulations is a crucial aspect of car ownership. A key component in this process is understanding Obd2 Emissions Readiness. Modern vehicles are equipped with sophisticated onboard diagnostic systems, and readiness monitors are at the heart of these self-checks. These monitors are essentially self-test routines that your car performs to assess its emission control systems. They provide valuable insights into your car’s health and are critical for passing emissions inspections. This guide will delve into the details of OBD2 readiness monitors, explaining what they are, why they matter, and how to ensure they are “ready” for your next emissions test.
What are OBD2 Emissions Readiness Monitors?
OBD2 Emissions Readiness Monitors, often simply referred to as readiness monitors or emissions monitors, are diagnostic routines designed to evaluate the performance of your vehicle’s emission control systems. Think of them as internal health checks for your car’s pollution control equipment. These monitors run in the background, automatically testing various emission-related systems to confirm they are functioning correctly.
Your car can perform up to 11 different system tests, each considered a readiness monitor. The result of these monitor tests indicates whether your vehicle’s computer has successfully completed the diagnostic checks. A “ready” status signifies that the system has been tested and has passed, meaning it’s operating within acceptable emissions standards.
Types of Readiness Monitors: Continuous vs. Non-Continuous
Readiness monitors are categorized into two main types: continuous monitors and non-continuous monitors. The fundamental difference 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 as they occur during normal vehicle operation.
Non-Continuous Monitors: Unlike their continuous counterparts, non-continuous monitors require specific conditions to be met before a test can be initiated and completed. These conditions can vary significantly depending on the particular monitor and the vehicle manufacturer. Some monitors might require a predefined drive cycle, which is a specific pattern of driving maneuvers, to activate the diagnostic test. Others may need multiple drive cycles, incorporating cool-down and warm-up periods.
Historically, the OBD2 standard (SAE J1979) distinctly categorized each monitor as either continuous or non-continuous. However, the latest revisions of the standard have removed this strict categorization for some monitors. Consequently, modern diagnostic tools like OBD Auto Doctor often reflect this change and may not rigidly adhere to the old classification.
Continuous or Non-continuous Monitors: Manufacturer Discretion
It’s important to note that for the following monitors, the classification as continuous or non-continuous can be determined by the vehicle manufacturer:
- Misfire Monitor
- Fuel System Monitor
- Comprehensive Components Monitor
Non-Continuous Monitors: Gasoline vs. Diesel Vehicles
Non-continuous monitors are further differentiated based on the type of engine: spark ignition (gasoline) and compression ignition (diesel).
Spark Ignition Vehicles (Gas)
- Catalyst (CAT) Monitor
- Heated Catalyst Monitor
- Evaporative (EVAP) System Monitor
- Secondary Air System Monitor
- Oxygen (O2) Sensor Monitor
- Oxygen Sensor Heater Monitor
- EGR (Exhaust Gas Recirculation) and/or VVT System Monitor
Compression Ignition Vehicles (Diesel)
- NMHC Catalyst Monitor
- NOx/SCR Aftertreatment Monitor
- Boost Pressure Monitor
- Exhaust Gas Sensor Monitor
- PM Filter Monitor
- EGR and/or VVT System Monitor
Alt text: OBD2 emissions readiness monitors displayed on a Windows computer screen using diagnostic software, showing a list of monitors with their status indicated by green checkmarks and red exclamation points.
Monitoring Cycles: Understanding “Since Reset” and “Current Drive Cycle”
To further understand readiness monitors, it’s important to grasp the concept of monitoring cycles. OBD2 systems typically report monitor status in two contexts:
1. Status Since Diagnostic Trouble Codes (DTCs) Cleared: This is the traditional and mandatory monitor status for all OBD2 compliant vehicles. It reflects the long-term status of the monitors since the last time the Check Engine Light was reset and diagnostic trouble codes (DTCs) were cleared. This status is crucial for emissions inspections as it indicates the overall readiness of the emission control systems after any repairs or resets.
2. Status for the Current Driving Cycle: Newer vehicles often provide an additional layer of information by reporting monitor status for the current driving cycle. These monitors reset and begin testing anew every time a new driving cycle starts (typically when the engine is started). This provides a real-time snapshot of monitor status during each drive. Older vehicles may not support this “current drive cycle” feature, in which case diagnostic tools will usually indicate the status as “NA” (Not Available).
Understanding Monitor Status: Complete, Incomplete, and Disabled
The result of each readiness monitor test is a monitor status, indicating the outcome of the self-diagnostic routine. The common status indicators are:
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Complete (Ready): This status signifies that the monitor test has been successfully completed, and the emission control system has passed the diagnostic check. Diagnostic software like OBD Auto Doctor typically represents this status with a green checkmark.
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Incomplete (Not Ready): This status indicates that the monitor test has not yet been completed. This could be because the necessary conditions to run the test have not been met, or the test has run and failed. An incomplete status is usually shown with a red exclamation mark in diagnostic tools.
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Disabled: In some situations, a monitor may be intentionally disabled for the current monitoring cycle. This often occurs when specific conditions prevent the monitor from running reliably. For instance, extreme ambient air temperatures (too high or too low) might disable certain monitors.
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Not Available (NA): If a monitor is listed as “NA” or “Not Available,” it simply means that the specific vehicle does not support that particular monitor. Not all vehicles are required to support every defined monitor.
Alt text: OBD2 readiness monitors displayed on an Android smartphone app, indicating that the vehicle does not support readiness monitors for the current drive cycle, as indicated by “NA” status for all monitors under “This Drive Cycle”.
Why is a Monitor Incomplete or “Not Ready”? Common Causes
Seeing an “incomplete” or “not ready” status for one or more monitors can be concerning, especially when preparing for an emissions inspection. Here are the most common reasons for incomplete monitor status:
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Recent DTC Clearing and Check Engine Light Reset: Clearing diagnostic trouble codes (DTCs) and resetting the Check Engine Light will invariably reset all readiness monitor statuses to “incomplete.” This is a standard procedure that occurs during or after vehicle repairs when diagnostic codes are cleared.
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Power Failure/Battery Disconnection: A loss of power, such as when the car battery is disconnected or replaced, will also reset the readiness monitor statuses. This is why it’s generally advised to avoid disconnecting the battery unless absolutely necessary. If battery disconnection is unavoidable, you’ll need to perform a drive cycle to reset the monitors.
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Start of a New Monitoring Cycle: For the “current monitoring cycle” status, it’s normal for monitors to initially show as “incomplete” when the engine is first started. These monitors begin testing from scratch at the beginning of each new drive cycle.
Implications for Emissions Inspections: It’s crucial to understand that depending on your location’s regulations, an OBD2-equipped vehicle may fail an annual emissions inspection if the required monitors (specifically the “since reset” monitors) are not in a “complete” state. For example, in the United States, EPA guidelines allow for a limited number of “not ready” monitors to still pass inspection. For vehicles from model year 1996 to 2000, up to two monitors can be “not ready.” However, for 2001 and newer vehicles, only a single monitor can be “incomplete” to pass. Exceeding these limits will result in inspection failure.
How to Get Monitors to “Complete” or “Ready”: The OBD2 Drive Cycle
Since readiness monitors are self-check routines, the most effective way to get them to a “complete” status is to drive your car. However, simply driving under normal, everyday conditions might not be sufficient to activate all monitors. This is where the concept of an OBD2 drive cycle comes into play.
An OBD2 drive cycle is a specific sequence of driving conditions designed to provide the necessary parameters for all (or most) readiness monitors to run their diagnostic tests. Following a drive cycle increases the likelihood of setting all monitors to “complete.”
Before attempting a drive cycle, ensure the following:
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No Check Engine Light/MIL (Malfunction Indicator Light): Make sure the Check Engine Light is not illuminated and that there are no active or pending diagnostic trouble codes. The presence of DTCs can prevent monitors from running to completion.
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Adequate Fuel Level: Some monitors, particularly the EVAP monitor, require the fuel tank to be between 35% and 85% full to initiate testing.
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Allow Time for Completion: In many cases, simply driving your car under a mix of city and highway conditions for about a week is sufficient to allow all monitors to reach a “complete” status naturally.
Generic OBD2 Drive Cycle Procedure
The specific drive cycle required for your car can vary depending on the make, model, and even the particular monitor in question. Vehicle manufacturers sometimes include specific drive cycle instructions in the owner’s manual. However, if a car-specific drive cycle is not available, the following generic OBD2 drive cycle can be used as a guideline. Keep in mind that this generic cycle may not work for all vehicles and all monitors, but it’s a good starting point. It is important to perform this drive cycle in a safe and legal area, away from regular traffic.
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Cold Start: Begin with a cold start. The coolant temperature should be below 50°C (122°F), and the ambient air temperature and coolant temperature should be within 11°C (20°F) of each other. This condition is typically achieved by letting the vehicle sit overnight for several hours. Ensure the ignition key is not turned to the “ON” position before the cold start, as this can interfere with the heated oxygen sensor diagnostic.
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Idle: Start the engine and let it idle in drive (for automatic transmissions) or neutral (for manual transmissions) for two and a half minutes. Turn on the air conditioning (A/C) and rear defroster if equipped to increase engine load.
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Moderate Acceleration and Steady Speed: Turn off the A/C and rear defroster. Accelerate smoothly and moderately to 90 km/h (55 mph). Maintain a constant speed of 90 km/h (55 mph) for three minutes.
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Deceleration: Decelerate to 30 km/h (20 mph) without using the brakes. If you have a manual transmission, do not depress the clutch during deceleration.
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Moderate Acceleration and Steady Speed (Higher Speed): Accelerate again to 90-100 km/h (55-60 mph) using approximately 3/4 throttle. Hold a steady speed of 90-100 km/h (55-60 mph) for five minutes.
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Stop: Slow down and come to a complete stop without using the brakes if possible.
After completing the drive cycle, use an OBD2 scanner or diagnostic tool to check the readiness monitor status again. It may take more than one drive cycle to set all monitors to “complete.”
Get Ready for Your Emissions Inspection: Be Proactive
To avoid failing your annual emissions inspection, it’s highly recommended to proactively check your vehicle’s OBD2 emissions readiness monitors before going for the official test. By doing so, you can identify any “incomplete” monitors and take steps to address them, such as performing a drive cycle.
In addition to checking readiness monitors, it’s also wise to read your vehicle’s diagnostic trouble codes (DTCs) before an inspection. Ensure there are no stored DTCs, as their presence will likely lead to inspection failure.
You can easily check both readiness monitors and DTCs using OBD Auto Doctor diagnostic software. Even the free version of the software allows you to read monitor statuses and diagnostic trouble codes. Why not try it now and ensure your vehicle is ready? Try the software right now
Remember, addressing potential emission issues promptly is not only crucial for passing inspections but also for maintaining your vehicle’s optimal performance, reducing fuel costs, and minimizing your environmental impact. Don’t wait until the last minute – be proactive and ensure your car is emissions ready!
