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Old 08-07-2019, 09:33 AM
NikonJeb NikonJeb is offline
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Default Setting EVAP monitors


I'm a hack mechanic in a one horse garage in central Pennsylvania with very little in depth experience with the Modis. I get by but this learning curve is ferocious. So understand that what I'm looking for is basic guidance as I'm frustrated and I don't have a ton of technical knowledge and experience that I can utilize this scanner to its fullest advantage.

I have run the service bay tests with select GM vehicles and that process does work. Is/are there similar processes for other vehicles? The vehicle I'm trying to set the EVAP monitor is a 2008 Odyssey 3.5. It's got miles, I need to set all monitors except one for the state's emissions machine to pass it. I have a limited amount of key cycles to do this as the vehicle has a lot of miles on it and it wants cats. This car's cats are prohibitively expensive for this single mother so we're trying to fly it without spending $1400+ of her money. As soon as the cat monitor flips, it throws a CEL. But I seem to get about a half dozen key cycles before that happens. If I can flip the evap monitor, I can get this thing through.

Thanks in advance for any help.
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Old 08-08-2019, 01:51 AM
Crusty Crusty is offline
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Crusty You made it!  You've done a great job ofearning reputation from your peers.  You now have secret access to a new hidden forum!


At least you have the gonads to call things as they are.
Hack may not be the right word. Inexperienced perhaps... We ALL have limitations of one way or another, just as we all have our positive traits.

I understand the predicament. Just because it has "miles" doesn't automatically mean it needs Cats though.
The allowance of ONE monitor incomplete was to allow people who need their cars repaired in the cold winter months to have incomplete EVAP monitors because they simply will not run to completion if temperatures are below about 37-F. Nor will they run in the summer when temperatures are above about 85-F.
OK, so we can use the "ONE" to ignore the CAT monitor but that means we HAVE to get the EVAP to run.

I'm no Honda expert, but I do know that their (and other Asian makes) valving and solenoids (usually above the tank) can be a PITA.
The fundamentals of all the EVAP systems are pretty standard.
Ambient above 37-F and below 85-F
ECT and IAT within about 5-F of each other upon cold start.
Cold start below 85-F
Fuel level above 15% and below 85%
If the fuel level is below 15% there is too much vapour area for the system to self test accurately or efficiently. This could take a longer time for the system to pull any sort of vacuum and hold (larger volume to pump down to a negative pressure)
If the fuel level is above 85% volume, it'll pull down quickly and may not accurately measure the decay back up to atmospheric pressure.
Then we have the key-off natural vacuum self tests after a run cycle that also tests for pressure leaks and not just a pumped down vacuum. Not all leaks show up under vacuum and not all leaks show up under pressure, but this strategy is usually on newer vehicles (but it became prevalent around 2004 to 2008)
As for the fuel level, I find it usually better if the fuel level in the tank is about 60 to 70%.
Read up on the GM EVAP systems. They have a pretty good description of operation. Also read up on the Chrysler "vacuum pump" (diaphragm pump) systems that is basically a VW system, and VW have some good TSB bulletins on their systems. Then read up on the other Asian makes for their EVAP strategies. The Asian systems are characteristically similar to each other.
Look for "pending" codes as well. Some codes that are almost going to set will inhibit the EVAP (or other} monitors to complete.
You could also make up your own EVAP test station by marking one inch lines on about eight feet of clear plastic tubing and making a big "U" taped to a broom handle, connecting one end of the open tube to some vacuum lines, epoxy a fitting through an old gas cap, plug or pinch off the air vent that goes to the charcoal cannister, and check the system yourself to see the system pulling about 6 to 12 inches of water column, just so you know there aren't any leaks.
Also look at the forum group on this site for the evap emissions.
Many times the self tests for EVAP will self test several times if it finds something "marginal". If the EVAp on the vehicle is in good shape they take less time to satisfy the ECM that it's OK and can "pass" quickly.
Sorry, no magic silver bullets.
Read up on the various EVAP codes and their "enable" to test criteria, and their "fail" criteria for the dirty little details.
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Old 08-08-2019, 02:32 AM
ephratah service center ephratah service center is offline
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one of the requirements is for engine coolant temp must reach 176 deg if you have a thermo stat that will not allow ect to reach at least 176 monitor will not set. You may want to go into global obd2 and do a health check for pending codes to see if there is a pending evap code also check mode 6 data under global obd. I had a nissian with bad cats that would not set evap monitor due to cats being bad the folks that design these vehicles do not share data like what order the monitors complete in or what happens if it sees a pending code. just saying it may halt the evap and cancel the evap test if it sees pending code for cat.Someone else may know more about this than me but hopes this helps some.
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Old 08-08-2019, 10:36 AM
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tech25 tech25 is offline
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tech25 Made it to level 2!  Looks like you are on your way to becoming famous


give it a try....
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