Dealing with a “Catalyst Monitor Not Ready” message during a smog check can be incredibly frustrating. You might be told to drive more, only to return and fail again. This article, created by experienced auto repair professionals at techcarusa.com, is designed to guide you through understanding and resolving this common issue, especially if you are considering using an OBD2 scanner for diagnostics.
Understanding the Catalyst Monitor and its Importance
In many regions, including California, vehicles model year 2000 and newer are subject to smog checks that rely on the vehicle’s onboard computer system. Instead of a traditional tailpipe emissions test, the focus is on whether your car’s computer has detected any issues that could increase emissions. A lit “check engine light” is an automatic failure, but even without the light, your car can fail if the system “monitors” are not in a “ready” state.
Monitors are self-tests performed by your car’s Engine Control Module (ECM) to ensure various emission control systems are functioning correctly. The catalyst monitor specifically checks the efficiency of your catalytic converter. If this monitor, among others, isn’t complete, your vehicle will likely fail the smog inspection.
Many drivers mistakenly believe disconnecting the battery will solve the problem by clearing fault codes. However, this action also resets the monitors to an “incomplete” state. Smog check systems are designed to detect this, making a simple battery disconnect ineffective.
Why is the Catalyst Monitor So Difficult to Ready?
The catalyst monitor is often the most stubborn monitor to set to “ready.” It requires specific driving conditions to run its diagnostic tests. These conditions involve a combination of vehicle speed, throttle position, and time. Simply driving around town is usually insufficient to activate the catalyst monitor.
There’s no magic mileage number to achieve monitor readiness. The key is meeting the necessary driving “conditions” dictated by your vehicle’s manufacturer.
Can You Pass Smog with a Not Ready Catalyst Monitor?
In many areas, the answer is no. Regulations often require all applicable monitors to be in a “ready” state for a vehicle to pass a smog check. However, there might be exceptions for some older vehicles in certain locations. It’s best to check with your local smog check station for the most up-to-date regulations.
How to Get the Catalyst Monitor Ready: Drive Cycles Explained
While there isn’t a universal drive cycle for every vehicle, understanding the concept is crucial. A drive cycle is a specific set of driving instructions designed by the manufacturer to initiate the catalyst monitor and other system tests in the shortest possible time.
These drive cycles can vary significantly between makes and models. Some can be quite complex and require precise execution. For example, one vehicle might require maintaining a steady speed of 50 MPH for ten minutes, while another could involve specific acceleration and deceleration patterns in a particular gear.
Cruise control can be a valuable tool for maintaining steady speeds during a drive cycle.
Example Drive Cycle Challenges:
- Steady Speed Requirement: Maintaining a constant speed, like 50 MPH for an extended period, can be difficult in normal traffic conditions.
- Specific Gear and Deceleration: Some drive cycles might require driving in a lower gear and decelerating without using the brake pedal, repeated multiple times.
Accessing the Correct Drive Cycle:
The most reliable source for your vehicle’s specific catalyst monitor drive cycle is the manufacturer’s technical information website. These websites often require a subscription. Reputable repair shops typically subscribe to these services and can provide you with the correct drive cycle for your car.
You might find “drive cycle” information through online searches, but be cautious. Information from forums and non-official sources may be inaccurate. Manufacturer-provided drive cycles are the most dependable.
A General Drive Cycle Approach (If Specific Instructions are Unavailable):
If you cannot obtain the exact drive cycle for your vehicle, a general approach that works for many cars involves:
- Freeway Driving: Find a freeway or highway where you can drive without interruption.
- Cruise at 60 MPH: Set your cruise control to approximately 60 MPH and drive for 10-15 minutes.
- Idle: Pull over safely and let the car idle for about a minute.
- Return Trip: Drive back in the opposite direction at a steady 60 MPH for another 10-15 minutes.
This general cycle may not work for all vehicles, but it can be effective for many.
A graph representing the catalyst drive cycle with speed and time plotted in a line graph. (Honda version)
This image illustrates a sample catalyst drive cycle, showing variations in speed and idle periods over time. Drive cycles are specific to vehicle makes and models.
When the Catalyst Monitor Still Won’t Ready: Deeper Diagnostics
If you’ve diligently followed the correct drive cycle and the catalyst monitor remains “not ready,” there might be an underlying mechanical or electrical issue preventing the monitor from running. It’s important to remember that monitors rely on sensors to perform their tests.
Oxygen (O2) Sensors are Key:
For the catalyst monitor, oxygen sensors are critical. The ECM uses data from the O2 sensors (typically located before and after the catalytic converter) to assess the converter’s efficiency.
Potential Issues Preventing Monitor Readiness (Even with a Good Drive Cycle):
- Marginal O2 Sensors: Even if O2 sensors are not completely failed and haven’t triggered a fault code, they might be performing poorly enough to prevent the catalyst monitor from running. The O2 sensor monitor itself might pass, but the catalyst monitor, which depends on accurate O2 sensor readings, may not.
- Undocumented Logic: Vehicle manufacturers sometimes incorporate undocumented logic into the ECM programming. This means there might be specific conditions or dependencies that must be met for the monitor to run, which are not publicly documented in service information.
- Hidden Faults: Issues like a faulty shifter position switch (as mentioned in the original article) could prevent the monitor from running if the ECM needs to know the car is in “drive” to initiate the test. The ECM might not explicitly flag the shifter switch problem with a code.
Using an OBD2 Scanner for Advanced Diagnostics:
This is where an OBD2 scanner becomes a valuable tool. While basic scanners can read and clear codes, more advanced scanners offer features that can help diagnose monitor issues:
- Monitor Status Check: Scanners can directly show the status of each monitor (ready or not ready).
- Live Data: Scanners can display real-time sensor data. By observing live data from O2 sensors and other relevant parameters during a drive cycle, you might identify anomalies or sensors that are not behaving as expected.
- Mode $06 Data (Onboard Monitoring Test Results): Advanced scanners can access Mode $06$ data. This data shows the results of the self-tests that make up the monitors. While raw Mode $06$ data can be complex, OEM-level scan tools often decode this information into a more user-friendly format.
Understanding Mode $06$ Data:
Mode $06$ data can reveal:
- Test Results: Which parts of the catalyst monitor test have run and passed, and which have not.
- Dependencies: It can show if the catalyst monitor test relies on other systems or sensors (like O2 sensors) and the results of those related tests.
By analyzing Mode $06$ data, you can gain insights into why the catalyst monitor is not completing. For example, if Mode $06$ data shows that the O2 sensor test is borderline passing, replacing a potentially weak O2 sensor might resolve the catalyst monitor issue.
Seeking Professional Help:
Diagnosing a persistent “Catalyst Monitor Not Ready” issue can be complex and may require specialized diagnostic tools and expertise. If you’ve tried the appropriate drive cycle and are still facing problems, consulting a qualified auto repair shop is recommended. Experienced technicians have access to advanced scan tools, manufacturer service information, and the diagnostic skills to pinpoint the root cause of the issue and get your vehicle ready for a smog check.
