OBD-II readiness & drive cycles
READY MEANS
THE TESTS RAN.
Readiness monitors are your vehicle computer’s emissions self-checks. This guide explains why they reset, what kind of driving often helps them complete, and when you need the exact manufacturer procedure for your year, engine, transmission, and fuel type.
One drive cycle does not fit every vehicle.
Exact enabling conditions are programmed by the manufacturer and can change within the same brand. Do not clear codes just to turn off the check-engine light; that resets the monitors and does not repair the problem. Follow traffic laws, never watch a scan tool while driving, and stop if the vehicle does not operate normally.
A safe general starting point
THE MIXED-DRIVING PATTERN
Many vehicles become ready through normal mixed driving. This is a general pattern—not a guaranteed substitute for the model-specific service procedure.
01
Cold soak if required
Let the vehicle sit—often overnight—so coolant and intake temperatures begin near ambient temperature.
02
Start and idle
Start without pressing the accelerator. Let the engine settle for a few minutes; some procedures require accessories to remain off.
03
City driving
Use gentle acceleration and normal stop-and-go driving for roughly 15–20 minutes, including several complete stops and idle periods.
04
Steady highway cruise
When traffic, road conditions, and posted limits allow, hold a steady 55 mph for 8 minutes. Use a light, steady throttle and avoid rapid acceleration or deceleration.
05
Safe coast-down
Only when traffic and road conditions make it safe, release the accelerator and coast from 55 mph to 15 mph without touching the brake or clutch. If conditions change, brake normally and try again another time.
06
More highway cruise
Accelerate smoothly back to 55 mph and continue a steady highway cruise for several more minutes. Then exit safely and recheck readiness with an OBD-II scan tool.
Brand-by-brand differences
THE BADGE ISN’T ENOUGH.
YEAR + ENGINE MATTER.
Ford · Lincoln · Mercury
Some older Ford owner guides describe a warm-engine sequence with extended idle, moderate acceleration to about 45 mph, a steady cruise, then 15 minutes of lower-speed city driving with several stops. Newer Fords and different engines can use different monitor-specific conditions, so verify the exact service information.
Common emphasis: warm-up, steady cruise, repeated city stops, and gentle throttle.
Chevrolet · GMC · Buick · Cadillac
GM service information uses an Inspection/Maintenance Complete System Set Procedure or monitor-specific procedures. Gas vehicles commonly need a cold start, idle, mixed driving, steady cruise, and coast-down. Some diesels may require multiple cold soaks and scan-tool-guided aftertreatment operation.
Common emphasis: identify the incomplete monitor first; diesel regeneration is a technician procedure when commanded.
Toyota · Lexus · Scion
Toyota commonly publishes a separate confirmation pattern for each monitor. Catalyst and oxygen-sensor monitors often need full operating temperature and steady driving. EVAP can depend on fuel level, ambient temperature, an overnight cold soak, and a key-off period. Use the model- and engine-specific repair manual pattern.
Common emphasis: strict preconditions—especially for EVAP—and monitor-specific patterns.
Dodge · Chrysler · Jeep · Ram
Stellantis procedures use monitor status from wiTECH and specify the enabling conditions for each incomplete monitor. Gas vehicles usually combine cold-start, cruise, deceleration, and idle conditions. Cummins and other diesels add DPF, NMHC/SCR, exhaust-temperature, and regeneration requirements.
Common emphasis: monitor-by-monitor conditions; diesel cycles can require extended varied driving or guided service.
For the exact procedure, have this information ready: model year, make, model, engine size, gasoline or diesel, transmission type, and the specific monitor that still says Not Ready.
Gas versus diesel
SAME WORD “READY.”
DIFFERENT SYSTEMS.
Gasoline & hybrids
Common continuous checks include misfire, fuel system, and comprehensive components. Non-continuous monitors may include catalyst, heated catalyst, EVAP, secondary air, oxygen sensor, oxygen-sensor heater, EGR/VVT, and—on some newer vehicles—gasoline particulate filter.
Light-duty diesel
Common monitors can include NMHC catalyst, NOx/SCR catalyst, diesel particulate filter, exhaust-gas sensor, boost pressure, EGR/VVT, fuel system, and comprehensive components. Completion often depends on exhaust temperature, load, DEF status, and regeneration history. Readiness time varies widely. Many monitors complete within several days, but some vehicle-specific cases take far longer. BAR documents the Exhaust Gas Sensor monitor on certain 2013–2016 Ford F-Series/Super Duty 6.7L and 2015–2019 Ford Transit 3.2L diesels taking up to 6,000–10,000 miles after DOC or DPF replacement while the degreening strategy completes. This is a special post-replacement condition, not a normal expectation for every diesel.
Diesel caution: do not attempt a stationary or forced regeneration from an internet checklist. A commanded regeneration can create extreme exhaust temperatures and should be performed only with the proper service information, equipment, location, and training.
Permanent codes: the 15/200 exception
For model-year 2010 and newer vehicles that support Permanent Diagnostic Trouble Codes (PDTCs), BAR says a stored PDTC is ignored by the Smog Check system after the vehicle has completed at least 15 warm-up cycles and traveled at least 200 miles since the OBD information was last cleared.
What counts as one warm-up cycle? The coolant temperature must rise by at least 40°F after the engine starts and reach at least 160°F. That is more than simply restarting a warm engine. In practice, the engine generally needs a substantial cool-down between qualifying cycles—often an overnight cold soak—so it can produce the required temperature rise.
WHICH MONITOR IS HOLDING YOU UP?
EVAP
On many vehicles, the EVAP monitor will run only when the fuel level is about ¼ to ¾ of a tank; a nearly empty or completely full tank can prevent the test. The vehicle often must sit with the key off—commonly overnight—so the fuel and tank can cool and the computer can check for pressure or vacuum changes during a cold-soak test. EVAP does not necessarily run every trip. It may take several normal drive, key-off, and refueling cycles for the fuel level and temperature conditions to line up. Exact requirements vary by year, engine, and manufacturer.
Catalyst or oxygen sensor
Usually needs full operating temperature, stable fuel control, steady cruise, and no related pending faults. A weak sensor or catalyst can prevent completion even after long driving.
EGR/VVT, secondary air, or heated components
These monitors may run only during a narrow temperature, load, RPM, or startup window. Manufacturer service information is especially useful when just one of these stays incomplete.
Diesel DPF, SCR/NOx, or NMHC catalyst
Check for active or pending faults, correct DEF quality and level where applicable, and normal regeneration history. These monitors can need sustained load and temperature or a professional scan-tool procedure.
California Smog Check readiness rules
California applies model-year, fuel-type, and vehicle-specific readiness standards, and BAR recognizes certain design-related exceptions. We use BAR’s current reference instead of relying on a generic “one monitor is allowed” rule.
Smog Dawg drive-cycle guides
STILL NOT READY?
Bring the year, make, model, engine, fuel type, and the monitor status. The Smog Dawg can help you understand what the vehicle is reporting and what comes next.