Facing a smog test failure due to unset readiness monitors? You’re not alone. Many car owners encounter this issue, often after a battery change or recent car repairs. OBD2 monitors are crucial for ensuring your vehicle’s emission system is functioning correctly and meeting environmental standards. This guide, based on expert automotive repair knowledge, will explain how to perform an OBD-II drive cycle to set these monitors and get your car ready for a smog check.
Understanding OBD2 Monitors and Readiness
OBD2 (On-Board Diagnostics II) systems are designed to monitor various aspects of your vehicle’s performance, especially those related to emissions. Readiness monitors are self-tests that the OBD2 system performs to confirm these systems are working correctly. If these monitors are not “ready” or “set,” it indicates that these tests haven’t been completed, which can lead to a smog test failure. Common monitors include:
- Oxygen Sensor Monitor: Checks the functionality of the oxygen sensors.
- Catalyst Monitor: Evaluates the efficiency of the catalytic converter.
- EGR System Monitor: Tests the Exhaust Gas Recirculation system.
- EVAP System Monitor: Monitors the Evaporative Emission Control system.
- Secondary Air System Monitor: Checks the secondary air injection system (if equipped).
- Fuel System Monitor: Evaluates the fuel delivery system.
- Misfire Monitor: Detects engine misfires.
Why Readiness Monitors Are Not Ready
Several factors can cause OBD2 monitors to be in a “not ready” state:
- Recent Battery Disconnection: Disconnecting the car battery often resets the OBD2 system and clears monitor statuses.
- Diagnostic Trouble Code (DTC) Clearing: Using a scan tool to clear DTCs also resets the monitors.
- Recent Car Repairs: Repairs related to the engine or emission system might require a drive cycle to reset monitors.
- Interrupted Drive Cycles: If a drive cycle is not completed properly, monitors may not set.
The OBD-II Drive Cycle Procedure
To set the readiness monitors, you typically need to perform an OBD-II drive cycle. This is a specific driving pattern that allows the OBD2 system to run all the necessary self-tests. Here’s a general OBD-II drive cycle procedure that can help set your monitors. Note that specific drive cycles can vary slightly by vehicle make and model, so consulting your vehicle’s repair manual for the most accurate procedure is always recommended.
Step 1: Cold Start
Begin with a cold start. This means the engine coolant temperature should be below 122 degrees Fahrenheit (50 degrees Celsius), and the ambient air temperature and coolant temperature should be within 11 degrees Fahrenheit (6 degrees Celsius) of each other. Crucially, ensure the ignition key is not turned on before this cold start, as it might prevent the heated oxygen sensor diagnostic from running.
Step 2: Initial Idle
Immediately after starting the engine, idle in drive for two and a half minutes. During this phase, turn on the air conditioning (A/C) and rear defroster to increase engine load. This step allows the OBD-II system to check the oxygen sensor heater circuits, air pump (if equipped), and EVAP purge system.
Step 3: Highway Driving – Part 1
Turn off the A/C and rear defroster. Accelerate smoothly to 55 mph (88 km/h) at half throttle. Maintain a steady speed of 55 mph for three minutes. During this constant speed driving, the OBD-II system monitors the EGR system, air pump, oxygen sensors, and canister purge, as well as checking for ignition misfires and evaluating fuel trim.
Step 4: Deceleration
Safely decelerate or coast down to 20 mph (32 km/h) without applying the brakes or depressing the clutch (for manual transmissions). This deceleration phase allows the OBD-II to check the EGR and purge functions under changing engine load.
Step 5: Highway Driving – Part 2
Accelerate again to 55 to 60 mph (88-96 km/h) at half throttle and maintain this steady speed for five minutes. This extended period at highway speed enables the OBD-II system to thoroughly monitor catalytic converter efficiency, misfires, EGR system, fuel trim, oxygen sensors, and purge functions.
Step 6: Final Deceleration and Stop
Finally, decelerate and come to a complete stop without using the brakes. This allows the OBD-II system to perform a final check of the EGR and canister purge systems.
After completing these steps, use an OBD2 scan tool to check the status of your readiness monitors. Ideally, they should all be set to “ready.” If some monitors are still not ready, you may need to repeat the drive cycle, or there could be an underlying issue preventing the monitors from setting, which might require professional diagnostic and repair.
Conclusion
Successfully setting OBD2 readiness monitors is essential for passing smog tests and ensuring your vehicle is running efficiently and cleanly. By following this OBD-II drive cycle, you can often resolve the issue of unset monitors. Remember to consult your vehicle’s specific service manual for the most accurate drive cycle and if issues persist, seek assistance from a qualified automotive technician. Understanding and addressing OBD2 monitor readiness is a key part of responsible vehicle ownership and maintenance.
