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  #11  
Old 01-05-2018, 04:05 PM
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Originally Posted by Crusty View Post
Once the key off portion of the test runs, does the scanner **** out and show NO DATA....
We have no way of knowing exactly WHEN it will complete and satisfy itself
This necessitates saving a movie every one or two minutes to see what it was satisfied with before it shuts down
In other words, does it STILL DUMP THE SAVED DATA FROM THE BUFFER-??
If you stay in the Service Bay Test, it will definitely give you a message that is is completed, along with the test result.

To answer the question of the scanner dumping the data when the PCM powers down, the answer is Yes. You lose it.

Joe
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Old 01-05-2018, 04:06 PM
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Originally Posted by diesel71 View Post
thanks for posting this joe ,it always helps seeing screen shots. does the pcm look for the 10 minute and 5 miles time to confirm the tank is warmed up? being a diesel guy I'm not sure if there's a fuel temp sensor.
The PCM does watch for both minutes and miles. That's the criteria it watches for and not tank temp. I don't recall ever seeing fuel temp on a GM car.

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Old 01-06-2018, 11:45 AM
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Originally Posted by Joe Rappa View Post
If you stay in the Service Bay Test, it will definitely give you a message that is is completed, along with the test result.

To answer the question of the scanner dumping the data when the PCM powers down, the answer is Yes. You lose it.

Joe
All the Service Bay test does is relax the temperature criteria from what it would do on its' own.
The code set criteria for the various P0440, P0441, P0442, etc identify what the ECM/PCM wants to see for it to perform it's own self tests.
You Rarely need to use the SBT. Just make sure the fuel level and the temperatures are within range and then the vehicle is driven enough to create under vehicle heat (from exhaust being under the vehicle in general proximity of the fuel tank)
It will check for sensor validation (capable of "0"), then check the vent valve & the purge valve for capabilities. After that it will close the vent, open the purge, and look for the fuel tank pressure sensor to pull down to a significant negative pressure. Once that is achieved, it will close the purge with the vent still closed and watch for the negative pressure (vacuum) to decay back to atmospheric very slowly (minimal small leak)
Once you stop and shut off the vehicle, it waits for the slosh to stop, check the pressure with the vent open (should be near the previously ascertained "0"). Then it will leave the purge closed (as it normally is with key off), then close the vent, then wait while under vehicle heat (warmth) increases tank pressure. It only measure in inches-of-water-column (13.6 inH2O in ONE inch of mercury). It's no different than a balloon in the sunny window or a black tire with the sun shining on it.
it stays closed until the pressure increases (usually in the neighbourhood of 8 or 9 inH20 ). Then it continues to monitor the low tank POSITIVE PRFESSURE, and waits as long as 45 minutes while the tank gradually cools down and loses pressure.
Once it is satisfied that the system can pull down and maintain a vacuum, it then checks that without any outside influences, that the system can also maintain a pressure.
If it can pull a vacuum and not decay quickly, and it can create a pressure and not decay quickly, it knows there isn't any leak.

One case the fuel tank LEVEL sensor had a VERY SMALL amount of variance (about 0.1 or 0.2 volts) and it didn't like the fact that the fuel level input was changing and it "completed" (both on its' own AND during SBT command) and it resulted in an inconclusive result.
THIS is WHY it is so important that the scanner does not dump the data that was automatically being saved by the scanner before the ECM shuts down.
It didn't like what it saw but there wasn't anything so grossly out of range that it flagged another code. It simply wouldn't "complete" after numerous cold starts and drive cycles.
The GM systems are very simple, and VERY LOGICAL systems. Not hard to diagnose IF WE HAVE ALL THE DATA to review after the fact.
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Old 01-06-2018, 12:59 PM
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I'm not very patient for waiting for Evap monitors to complete, so next time I'm probably going to direct my Salamander heater under the gas tank until I hear a train whistle sound coming out of the tank vent.
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Old 01-06-2018, 07:11 PM
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All the Service Bay test does is relax the temperature criteria from what it would do on its' own.
I use it a decent amount when trying to get cars through an emissions inspection. The cool thing about the EONV cars is that if it runs successfully it will run every monitor. You do have to give it a sensible road test, but it works great when I need it.
I've never seen anything published about it running all the monitors, but it sure acts that way when I use it.

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Old 01-07-2018, 02:17 AM
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I use it a decent amount when trying to get cars through an emissions inspection. The cool thing about the EONV cars is that if it runs successfully it will run every monitor. You do have to give it a sensible road test, but it works great when I need it.
I've never seen anything published about it running all the monitors, but it sure acts that way when I use it.

Joe
That's not a function of the Service Bay Test. The conditions required to run the test from cold start, then the idle portion followed by the drive portion facilitate the other monitors by happenstance.
We're also told (and forced) to clear codes to initiate this bi-directional command. If there were other codes, or incomplete monitors (such as O2 codes), we usually concentrate on fixing those other issues before we address the EVAP system as we look upon them as more significant.
This means the other monitors and systems are likely closer to optimum so they complete easily.
I've seen what you have seen but I've also seen many times other monitors are still incomplete. As I said, it's not a function of the SBT.
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