You've driven your vehicle to the emissions test station to have it tested, but your vehicle was rejected because it was "Not Ready." What exactly does "Not Ready" mean? It means your Onboard Diagnostic System (OBD II) has NOT completed all of its self-test monitors that keep an eye on the performance of your emissions control systems. Depending on the year, make and model of your vehicle, there may be half a dozen or more OBD monitors that must have completed. A single or multiple "NOT READY" indications will prevent your vehicle from passing the emissions inspection.
To pass an OBD II plug-in emissions inspection test, all of the OBD monitors must have run and successfully completed with no faults found. This tells the emissions test computer that your vehicle is performing within emissions limits for your year, make and model, and that your vehicle is in compliance with the applicable emissions laws, and that your vehicle is not polluting.
The OBD system monitors some functions every time you drive your vehicle, but only checks other functions under certain driving or operating conditions. Some checks are "continuous" and are ongoing all the time. The continuous checks include:
The OBD monitors that only run under certain conditions include the EVAP monitor, HEGO monitor (Heated Exhaust Gas Oxygen sensor), and the Catalyst Efficiency monitor.
Three OBD monitors on this vehicle are NOT READY:
the Catalyst, EVAP and HEGO oxygen sensor monitors.
EVAP Monitor Not Ready
The EVAP (Evaporative Emission Control System) monitor checks for fuel vapor leaks (including a loose or missing gas cap). As a rule, the EVAP monitor only runs when certain conditions have been
met. If these conditions have not been met since the last time the monitor ran, or since the last time the battery was
disconnected, or since the last time fault codes were cleared from the PCM memory, the EVAP monitor will NOT be ready.
EVAP Drive Cycles
The following are sample drive cycles for the EVAP monitor:
Ford: With fuel tank one half to three-quarters full, cruise at 45 to 65 mph for 10 minutes. Avoid sharp turns and hills during this period.
Chrysler: There are two-parts to this test. The first part runs after idling for five minutes, then driving at 30 to 45 mph for two minutes (fuel tank must be half to 85 percent full). The second part runs after the vehicle has sit for 8 or more hours (cold soak) without being driven. Start the engine and idle for four minutes, then drive in stop-and-go traffic for five minutes using smooth accelerations and decelerations. Stop and idle for 4 minutes. The EVAP monitor should be complete.
HEGO Monitor Not Ready
The Heated Exhaust Gas Oxygen sensor monitor makes sure the oxygen sensors are functioning properly and
are operating within their normal range. The monitor runs after the engine has reached normal operating temperature, and the vehicle is cruising at a specified speed for a specified length of time. This monitor will not run if there are any faults in the oxygen sensor heater circuit, if there are any pending oxygen sensor codes, or the engine coolant or vehicle speed sensors are not functioning normally.
HEGO Drive Cycles
The following are some sample drive cycle requirements for the HEGO monitor to run:
Ford: The HEGO monitor should run when the engine has reached normal operating temperature, the inlet air temperature is between 40 and 100 degrees F, and the vehicle is cruising at a steady 40 mph for four minutes.
GM: GM uses a two-part HEGO monitor. The first part of the HEGO monitor runs after idling the engine for two and a half minutes with the A/C and rear defroster on. This checks the O2 heater circuit. After this, turn the A/C and defroster off, then accelerate at halt throttle to 5 mph and hold at a steady 55 mph for three minutes. This will complete the second half of the HEGO monitor that checks the responsiveness of the O2 sensors.
Chrysler: Idle for five minutes (to reach closed loop operation). Then drive at a steady vehicle speed above 25 mph for two minutes. Stop and idle for 30 seconds. Then smoothly accelerate to 30 to 40 mph. Repeat the last two steps five times.
Toyota: The HEGO monitor should run after idling the engine for nine minutes, then driving at a steady 25 mph for two minutes.
Catalyst Efficiency Monitor Not Ready
The Catalyst Efficiency Monitor verifies the catalytic converter is operating at high enough efficiency to keep
exhaust emissions within acceptable limits. The monitor compares the signals from the upstream and downstream oxygen sensors
to monitor the operation of the catalytic converter. If catalyst efficiency has dropped below a certain threshold, this
monitor will set a converter fault code (P0420 and/or P0-439) and turn on the Check Engine light.
Catalyst Monitor Drive Cycles
The following are some sample drive cycles for the catalyst monitor to run:
Ford: The catalyst monitor will not run until the HEGO (oxygen sensor) monitor has run and completed successfully with no faults found. The vehicle must then be driven in stop-and-go traffic conditions at five different cruise speeds ranging from 25 to 45 mph over a period of 10 minutes.
GM: The catalyst monitor runs after cruising at 55 mph for 5 minutes, but it make take up to five drive cycles at this speed before the monitor will run!
Chrysler: The catalyst monitor will NOT run unless the Check Engine light is off, no fault codes are present, the fuel level is between 15 and 85 percent full, and the coolant temperature is above 70 degrees F. If these conditions have been met, the engine must have run at least 90 seconds, and the engine speed must be between 1,350 and 1,900 rpm. Idle vehicle for five minutes (to reach closed loop operation), the drive at a steady speed between 30 and 45 mph for two minutes.
Toyota: The catalyst monitor will run after driving the vehicle at 40 to 55 mph for seven minutes, followed by driving at 35 to 45 mph for another seven minutes.
Just because a scan tool check shows no codes found doesn't mean your vehicle will pass emissions.
All of the OBD monitors must also be complete for your vehicle to be test ready.
On this Innova scan tool, the emissions ready status is shown with colored LED lights.
GREEN means no faults and the vehicle is ready to pass.
YELLOW means one or more OBD monitors have not completed and the vehicle is NOT ready for testing.
RED means one or more fault codes. Repairs are needed before the vehicle will pass.
Common Causes of Not Ready Rejection for Emissions Testing
All of the applicable OBD monitors for your year, make and model of vehicle must have run and completed to be accepted
and pass an OBD plug-in emission test. Any of the following may cause your vehicle to not be ready:
On this Innova scan tool, the OBD emissions monitor status is shown at the top of the screen.
Any monitors that are flashing are NOT ready. If all of the indicators are dark, it means all have passed and the vehicle is ready for testing.
Scantool Companion software can help you diagnose your engine.
Larry's Guide to Check Engine Light Diagnostics (PDF ebook)
More OBD II Related Articles:
Check Engine Light OnBoard Diagnostics
More on Check Engine Lights & Diagnostics
Diagnostic Tips for Trouble Codes
Other Warning Lights (TEMP, OIL, ALT/GEN, BRAKES, ABS, AIR BAGS, etc.)
Scan Tool Diagnostics
Decoding Onboard Diagnostics
TROUBLE CODE Help
Understanding OBD II Driveability & Emissions Problems
Zeroing in on OBD II Diagnostics
Controller Area Network (CAN) Diagnostics
CAN communication problem (what to do when the CAN system won't talk to your scan tool)
Troubleshooting Intermittent Engine Problems
Troubleshoot Engine Stalling Problems
Mode 06 Diagnostics
Help with DTC P0300 Random Misfire Codes
Troubleshooting a P0420 Catalyst Code
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