GM EVAP Service Bay Test

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  • Joe Rappa
    Snap-on DSD
    • Aug 2007
    • 2050

    GM EVAP Service Bay Test

    I had to fool with a Chevy van the other day. It needed a bunch of work, but also had a bad purge valve. In order to get it through NC State Inspection, I needed to get the Monitors to run. I ran the Service Bay Test to do it.
    I recorded the data while I did it. I figured I'd post the data to show how this test runs.
    Remember that this Test takes place after the key is turned off. It requires 10 minutes and 5 miles of driving to warm the fuel tank up. Then it needs to sit and cool off, so vacuum can develop.
    Attached Files
    "You don't build a reputation on what you're going to do"
    Henry Ford
  • SnapOnKid
    Senior Member
    • Jan 2011
    • 870

    #2
    Cool.

    Is this now an option to see the data and log it during the testing process?

    Comment

    • Joe Rappa
      Snap-on DSD
      • Aug 2007
      • 2050

      #3
      Originally posted by SnapOnKid
      Cool.

      Is this now an option to see the data and log it during the testing process?
      You know, I don't know if that's available or not. That's not how this was recorded anyway. Once you get past the high idle portion of the Service Bay Test and start the driving portion, the car is done looking for commands from the scanner. You can back out of the test and watch live data. That's what I did here because I wanted to watch all the monitors run.

      Joe
      "You don't build a reputation on what you're going to do"
      Henry Ford

      Comment

      • SnapOnKid
        Senior Member
        • Jan 2011
        • 870

        #4
        Originally posted by Joe Rappa
        You know, I don't know if that's available or not. That's not how this was recorded anyway. Once you get past the high idle portion of the Service Bay Test and start the driving portion, the car is done looking for commands from the scanner. You can back out of the test and watch live data. That's what I did here because I wanted to watch all the monitors run.

        Joe
        I was not aware of this. It would be nice to be able to see that info during the testing process so you can see if it's hitting the correct marks.

        Comment

        • Witsend
          Banned
          • Nov 2012
          • 2942

          #5
          I had to fool with a Chevy van the other day. It needed a bunch of work, but also had a bad purge valve. In order to get it through NC State Inspection, I needed to get the Monitors to run. I ran the Service Bay Test to do it.
          I recorded the data while I did it. I figured I'd post the data to show how this test runs.
          Remember that this Test takes place after the key is turned off. It requires 10 minutes and 5 miles of driving to warm the fuel tank up. Then it needs to sit and cool off, so vacuum can develop.
          So after evap system repairs you only need to drive or run a vehicle for 10-15 minutes and then running the GM Evap service bay test for 35 minutes KOEO will also complete that stubborn EVAP monitor as well as giving you a general pass -fail for the service bay test result? Did you have to hook up a battery maintainer so them damn rotten GM DRLs don't drain the battery? The present temperature here in Illinois is around 0 degrees, so I don't think the gas tank temperature would increase enough to run the test

          Comment

          • Joe Rappa
            Snap-on DSD
            • Aug 2007
            • 2050

            #6
            Originally posted by Witsend
            So after evap system repairs you only need to drive or run a vehicle for 10-15 minutes and then running the GM Evap service bay test for 35 minutes KOEO will also complete that stubborn EVAP monitor as well as giving you a general pass -fail for the service bay test result? Did you have to hook up a battery maintainer so them damn rotten GM DRLs don't drain the battery? The present temperature here in Illinois is around 0 degrees, so I don't think the gas tank temperature would increase enough to run the test
            Actually the Test runs after you shut the car off. The whole test runs like this:
            Make sure the EVAP Monitor is not completed.
            In the Functional Test Menu on a GM vehicle, select EVAP Service Bay Test.
            The scanner requests you hold the vehicle at high idle. It actually gives you a min/max, but you can ignore that. It just needs to be high idle. Hold it there for 10 minutes, or until the scanner shows that portion of the test is complete.
            Now, if the car is older than around 2006, that is the limit of the test, and the scanner will tell you if it passes or fails.
            If the car is newer, and uses EONV (Engine Off Natural Vacuum) to test the car, it will tell you to drop it in gear and go for a ride. You may have to drive 10 minutes and 10 miles to warm up the tank.
            Then the scanner will tell you to shut the car off. You don't need to do it immediately, so drive back to the shop and shut it off. This is the portion of the test that is recorded above.
            Here's how you know of it is in EONV System. Answer is found in the Mode 6 section of your service info.
            This car also specs that it has to be over 32F for the test to run.
            Attached Files
            "You don't build a reputation on what you're going to do"
            Henry Ford

            Comment

            • Witsend
              Banned
              • Nov 2012
              • 2942

              #7
              Thanks Joe for the good description of how the service bay test works , but my question remains...Will running the GM Evap Service Bay test besides a pass fail result for this test run, also complete the Evap Monitor so you can just run The Turd over to the test lane sooner than a couple days later.

              Comment

              • Steve6911
                Moderator
                • Feb 2007
                • 2168

                #8
                To answer your question Wit, yes it will. Even the older test where you didn't have to drive the vehicle would set the Readiness Monitor. Several other makes also allow you to do this.

                Comment

                • Crusty
                  Senior Member
                  • Dec 2007
                  • 2450

                  #9
                  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-??

                  Comment

                  • diesel71
                    Senior Member
                    • Feb 2008
                    • 921

                    #10
                    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.

                    Comment

                    • Joe Rappa
                      Snap-on DSD
                      • Aug 2007
                      • 2050

                      #11
                      Originally posted by Crusty
                      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
                      "You don't build a reputation on what you're going to do"
                      Henry Ford

                      Comment

                      • Joe Rappa
                        Snap-on DSD
                        • Aug 2007
                        • 2050

                        #12
                        Originally posted by diesel71
                        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.

                        Joe
                        "You don't build a reputation on what you're going to do"
                        Henry Ford

                        Comment

                        • Crusty
                          Senior Member
                          • Dec 2007
                          • 2450

                          #13
                          Originally posted by Joe Rappa
                          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.

                          Comment

                          • Witsend
                            Banned
                            • Nov 2012
                            • 2942

                            #14
                            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.

                            Comment

                            • Joe Rappa
                              Snap-on DSD
                              • Aug 2007
                              • 2050

                              #15
                              Originally posted by Crusty
                              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.

                              Joe
                              "You don't build a reputation on what you're going to do"
                              Henry Ford

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