In the old days of OBDI, you could reset the computer and run your vehicle over to the emissions testing station. Not anymore. Everytime you clear the codes from the computer, it basically reboots and starts all the testing routines over again from scratch. Each “drive cycle” routine has its own parameters to meet before it sets a “readiness monitor.” If the readiness monitor isn’t set, the testing station will see that immediately and send you packing.

Here’s an example of a drive cycle readiness routine for a Chevrolet Trailblazer.

At least 17 hours have elapsed since the last drive cycle met and passed the test criteria. That means you can’t clear codes and immediately try to perform a drive cycle and zoom off to the testing station. Remember, minimum of 17 hours.

Check engine light is off.

No Emission related trouble codes are present.

BARO signal more than 74 kPa.

Battery voltage between 10-18v.

Difference between the ECT and IAT signals less than 14ºF at startup. In other words, the two sensors must be good.

Engine coolant temp between 39-86ºF at startup. Can’t start this test on a sub-zero day.

Intake air temp signal between 39-86ºF at startup.

Fuel level between 25-75%.

If you meet all those criteria, then

1. Start the engine and allow it run at idle speed for 15 seconds.
2. Accelerate at part-throttle to 45 mph and maintain that speed until the engine reaches normal operating temperature (this can take up to 10 minutes).
3. Drive for another 3 minutes at 45 mph on a flat road without climbing any hills to minimize the fuel slosh. Bring the vehicle to a stop in a safe place, but do not turn off the
ignition key.
4. On the scan tool or code reader with readiness monitor feature, check the status of the readiness code for the EVAP System Monitor. The Readiness code should change to
YES when the test is done. If it does, return home turn off the ignition key.

If it does not, check for any temporary codes. If no temporary codes are set, return to step 3 and repeat the test procedure. Check the status of the Readiness code for the EVAP System Monitor. The Readiness code should change to YES when the test is done.

NOTE:
Extremely high or low ambient temperatures may prevent this test from running. If the test is interrupted before completion, do all of the test steps from the beginning. If a small leak is detected during testing, a minimum of 3 drive cycles may be required before the EVAP Monitor status will update to YES. Performing a visual inspection prior to running the EVAP test may prevent having to repeat the test. An aborted or failed test will require the vehicle to cool down in order to meet the test conditions to run another test sequence.

For more information on this repair or any others for your vehicle, buy an online subscription to either Alldatadiy.com or eautorepair.net. Click on this link to compare the two services: Compare Alldata and Eautorepair.

If you just need information for a single repair and want to save money,eautorepair offers a lower price 1-week subscription for only $11.99. Or, if you’ll be working on this vehicle in the future, you can buy a 1-year subscription (Alldatadiy.com for $26.99, or eautorepair.net $29.99)

© 2012 Rick Muscoplat

Alldata and Eautorepair are both professional grade shop manuals. You’ll find more in-depth information and more complete wiring diagrams, along with descriptions of how the systems work. And, you’ll get all that at a price you can afford. Check them out!

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