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I'm aware of two related issues here

  1. Does Check Engine Light Clear Itself...
  2. I need the correct 2010 ... drive cycle steps to clear a “Permanent ” P0456 code

I've just completed a particularly nasty repair on a Mazda3, where the top of the fuel delivery module lock ring had a crack in it, and was leaking. I'm trying to get clean before going to the state to get a retest.

  • I know if you clear codes, then drive to the local emission testing station that will get you an immediate rejection.

Edit here... not sure why folks are having trouble understanding this one... Its called a "not ready" failure.

New York has adopted the federal Environmental Protection Agency (EPA) guidance concerning readiness during OBD II inspections. A vehicle will fail the (NYVIP2) OBD II inspection if enough monitors are reported as Not Ready.

Any of the following may cause your vehicle to not be ready:

Disconnecting the battery for any reason. This erases the memory in the PCM, including stored fault codes and previous OBD monitor test results. It's like resetting the clock back to zero. Consequently, it may take several days (or even weeks) of driving before all of the monitors will run, allowing your vehicle to be tested.

Erasing stored codes with a scan tool. This also resets all of the monitors back to zero, so allow plenty of time for the monitors to run before driving back to the emissions test facility. If any of the erased fault codes reappear, it may prevent one or more of the monitors from completing.

My state has exactly the same criteria as New York. end of edit...

  • Based on that, I was thinking that my best course of action was to not clear any stored codes, and do drive cycle testing up until the point the check engine light went out on its own. This is the generally the recommendation in "Does the check engine light clear itself..." posting.

Here's my only issue... While doing web searches to understand the drive cycle required to clear codes, I ran across the State of New York Vehicle Inspection Program website. That site is extremely detailed, and of high quality content.

Something there really caught my eye. On the page for "Helping Set Monitors" I see

An example of some common enabling criteria to run the EVAP monitors drive cycle:

  • The malfunction indicator lamp (MIL) must be off <--- HUH??!?
  • Barometric pressure exceeds 75 Kpa
  • At start-up, IAT and ECT is between 45°F and 85°F
  • IAT is not more than 2°F greater than ECT
  • ECT is not more than 12°F greater than IAT
  • Fuel tank level is between 26 percent and 74 percent
  • The TPS is between 9 percent and 35 percent
  • The EVAP solenoid is at 50 percent pulse width PWM, within 65 seconds of engine run time

Abbreviations: IAT - Intake Air Temperature, ECT - Engine Coolant Temperature, TPS - Throttle Position Sensor, PWM - Pulse Width Modulation

Whoa.... look at that first item, the malfunction indicator lamp (MIL) must be off As I read that, and if its true, that would mean, no matter how much drive cycle testing I do, no way will I every be able to clear the MIL lamp. This seems to directly contradict Does Check Engine Light Clear Itself... posting. I've been out on the highway performing testing, and everything in the current drive cycle shows passed, EXCEPT Evaporative System, sigh.

Anybody been here before? Any hints and tips on how to get thru a US state emission test, after a successful repair? Yes, its possible that I missed something on my fuel delivery module lock ring repair, but I don't think so.

Do I stay the course, keep doing the recommended test drives until the lamp goes out, or do I clear the codes, then do test drives?

If I do instead decide to clear the codes, how much testing on a clean slate is required to get a go at the inspection station?

Anybody been here before? thanks...

  • How will the testing facility know that you've cleared codes? More importantly how would any vehicle that has ever had a code pass inspection? I think your information in inaccurate. If the problem that caused the codes to be set is resolved and you clear the codes, then you will be good to go. – jwh20 Oct 7 at 9:32
  • Many codes don't clear themselves and have to be cleared, sometimes cars won't run properly unless they are cleared. Either I don't understand the question or it's based on incorrect information about the inspection process. – GdD Oct 7 at 14:20
  • Question updated to describe the "Not Ready" condition brought about with cleared codes. Its not an opinion. Its accurate. I was surprised by that as well, but its solid info. I would have thought the testing station runs the test when plugged in. Apparently not. Apparently it uses testing history stored in OBDII system. And it needs to ensure that stored history is of high integrity. But my question now is.. Do I clear codes and conduct multiple drive cycles? or keep performing multiple drive cycles and pray the check engine light goes out on its own? – zipzit Oct 7 at 14:38
  • @zipzit Thanks for the updated information. If the specific fault code you're having does clear itself on your vehicle (not all do this) then if you have fixed the problem the light should clear after a few miles of driving. If not, then I guess your best bet is to clear the code, and drive around long enough for whatever they are looking for to be true. Unfortunately they do NOT provide an answer to that question. – jwh20 Oct 7 at 18:34
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I wanted to followup on this one, in case anybody else gets here.

Brief review: In many (all?) states within the USA, an annual emission / SMOG test is required at the time of registration renewal. In my state, they follow the guidance from the federal Environmental Protection Agency (EPA) concerning readiness during OBD II inspections. In simple words, the manufacturers OnBoard Diagnostics (OBD-II) system is used as the reporting mechanism for meeting emission standards. They don't generally perform tailpipe emission tests any more (at least on vehicles built after '96 gas / '97 Diesel). Instead they read the results stored in the I/M (Inspection / Maintenance) test portion of the OBDII, and stored fault codes.

  • You can't just clear out the fault codes, drive to your local emission verification station and get a pass. You will fail. See comments above.
  • The testing / drive cycles required to exercise all of the I/M tests takes a significant amount of time to perform. The evap test was by far, the most difficult.
  • The general guidance to just drive the car for 100 or 200 miles over X days might work and it might not. That's not great guidance.
  • The absolutely best practice is to find the Specific On-Board Diagnostic test for your make, model and model year of your vehicle. I was surprised how different these descriptions were. The details for the Onboard-Diagnostic test are listed in the factory service manual. Take the time to find the correct reference. I ran a 2010 test on a 2008 model year car (that was initially the only shop manual I could find) and the test did not perform. It didn't fail, it didn't pass, it just didn't run.
  • The Evap leak test was a pain, and was easily the most difficult test to get sucessfully completed. In my case, I had a bunch of odd requirements. (Start the car, idle for ten seconds, shut off car for five hours, start engine, idle for 15 minutes, ... etc...) Huh? Five hours? How did that get in there? With all the wait times, I found it best to run the test just once per day.
  • In my case there was a safety aspect of the testing... You had to drive the car at 45 miles per hour for a very long period of time; thank you cruise control. Where are you going to do that safely? I chose to do that part of the test on the freeway, late at night, when there isn't much traffic. Believe me, driving 45 MPH when the normal flow of traffic is 70 MPH is a safety issue. Use the four way flashers. Stay safe.
  • Bring a stop watch (NOT your phone) to time your activities. When I did the testing EXACTLY as listed in the Service Manual I got valid test results... I used the cell phone for other ELM / OBD feeds.
  • I still don't fully understand when the actual Evap bleed down test is performed in the drive cycle. I suspect its during shutdown after one of the longer 45 MPH drives.
  • The shutdowns are timed. When the vehicle is shut off, REMOVE the Key from the ignition. I'm not positive, but I think I failed / missed one test completion because of this. I've read that on some vehicle lines, key in ignition keeps some circuits energized to enable quick startup. For best testing results, when key off, remove the key from the ignition.

And for reference, here are two of the screens I used during the drive.

OBD2 Screen for Evap Test Drive

OBD2 Screen for Evap Test Drive #2

And as for the original question above, I still don't know if its better to leave the check engine light on (i.e. Not clear the codes) then perform the appropriate on-board diagnostic test, or clear the codes and retest. The shop manual for my car told me to clear the fault codes (after I performed the repair) and do the Onboard Diagnostic tests so that's what I did. And the minute that I first got a completion of the evap test, it was a pass. I will say I ran the evap test four times trying to get a successful completion. All the other tests were pretty easy to perform. I didn't get that until I found exactly the correct service manual page for my make, model and model year and ran it EXACTLY as directed. The general guidance to just drive the car around town and accumulate mileage, heck no. Work smarter, not harder.

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Evap systems can fall foul on even small leaks but NO AMOUNT OF DRIVING will clear them...the leak needs to be identified.. and rectified.. the evap systems syhpons vapours off the combustion cycle and passes them back when the engine idled but it's got many small plastic components and are fairly prone to breaking down...

  • oops. Thanks for sharing. Welcome to mechanics.stackexchange. Not sure you are on point, but I appreciate that you are trying to join the activities... Probably best to read the questions posted once or even twice before responding though. Focus on sentences that end in a question mark (?) No offense intended. – zipzit Oct 7 at 22:26
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The monitors will all reset at power removal. Just run the vehicle for enough time to recycle through the monitors which is about 100 miles of mixed driving (highway and city). I have not had issues with evap system but with cat system which took the 100 miles without another error code. I suspect the evap is the same. PS the vehicle was a 2000 Sienna - I reset the codes and the owner took the vehicle for inspection but they told him to take it to a nearby city and back (about 100 miles). He returned the next morning and it inspected with no issues. He drove it for several months since without failing again.

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