Help with Tech2

[t_bergman]

Needing to get the emissions tested on my '13 Yukon XL 2500 and the EVAP/O2 sensors are showing as not ready, I've already failed once and have 0 DTCs coming alive.

Does anyone have a procedure doc on how to run the evap service bay test with a Tech2Win?

I want to also ensure I am getting into the vehicle correctly when going into the Tech2, if anyone has a guide on the various 1/2 options as I've got a 2500 with the L96.

It doesn't get driven heavily however I've used it as my daily driver since 7/5 when it first failed and in I/M status the EVAP and O2 sensors are still not ready.

 

[Joseph Garcia]

For starters, take a look at this. I've also attached copies of the Tech 2 User Manuals

The EVAP (Evaporative Emission Control) Service Bay Test, often performed with a Tech 2 scan tool, is a diagnostic procedure used to verify the integrity of a vehicle's EVAP system, which controls fuel vapor emissions. It's a functional test that simulates driving conditions to identify leaks or other issues within the system.

Here's a breakdown of the process:
1. Accessing the Test:

• The Tech 2 scan tool is connected to the vehicle's OBD-II port.
• Navigate to the EVAP Service Bay Test within the scan tool's functional test menu.

2. Preparing for the Test:

• Ensure the vehicle's fuel level is between 15-85% and the engine coolant temperature is below 158°F (70°C) according to ATech Training, Inc..
• The engine should be running.

3. Running the Test:

• The Tech 2 will guide you through the test steps.
• The test may involve holding the engine at a high idle or performing a drive cycle.
• Some tests require a specific engine speed (RPM) and load (e.g., 1800-2200 RPM).
• The scan tool will monitor various EVAP system parameters (e.g., purge valve, sensors).
• The test may include a drive cycle where you drive the vehicle for a set distance and time (e.g., 10 minutes, 10 miles).
• Some tests require the engine to be shut off after the drive cycle.

4. Interpreting Results:

• The Tech 2 will indicate whether the EVAP system passed or failed the test.
  
  
• If the test fails, it indicates a potential leak or other issue in the EVAP system.

5. Post-Test:

• If the test involves a drive cycle, return the vehicle to the bay and shut off the engine while connected to the Tech 2.
• The Tech 2 will perform an engine-off test, which is sometimes documented and sometimes not, according to a forum post.

Key Considerations:

• Some older vehicles (e.g., pre-2006) may have a simpler EVAP test procedure using the Tech 2.
• Newer vehicles may use Engine Off Natural Vacuum (EONV) for testing, which involves a drive cycle after the initial high idle.
• The specific steps and requirements can vary by vehicle make and model.
• It is important to follow the Tech 2 prompts and consult service information for the specific vehicle being tested.

 

[t_bergman]

I am immediately getting an "Engine Running Test Aborted Lost Enable Conditions"

From what I have been able to gather, the solenoid is not sealing the system when the test starts which is not allowing the system to build vacuum. If I go into the EVAP Purge/Seal commands and increase to -5.5mmHg then seal the system I am seeing a slow drop to -4.8mmHg. That indicates to me that there is a leak somewhere however not enough of a leak to issue the P0442 code as I have 0 DTCs or pending DTCs on the car.

The truck is from CA and so if something is cracked just enough to cause a vacuum issue but not to throw a code, that would make sense. Trying to figure out next course of action here as emissions are due in 6 days.

 

[Fless]

If the purge and seal test indicates a leak, then you may want to check the function of the purge valve on the engine, and the vent valve in the back of the vehicle by the spare tire. Each can be removed from the truck and bench tested.

The purge valve should be closed with no 12vDC applied to the connectors, but open when 12vDC is applied.

The inverse is true of the vent valve -- open with no 12vDC applied, and closed (sealed) when 12vDC is applied.

Test can be done simply by connecting/disconnecting 12vDC to the terminals (polarity doesn't matter for the bench test) and by trying to blow through one of the hose connections. Switch the 12v off and on to verify that the valve is operating correctly all the time and not being intermittent.

Your next test might need to be a smoke test.

 

[t_bergman]

Just to close the loop, ended up doing a modified drive cycle for the O2 readiness sensor which ultimately allowed me to pass emissions. Everything Fless mentioned above was working correctly, no P0442 code and a dealer I trust said to not even bother chasing down EVAP anymore.

Here's the drive cycle which I followed:

-Start without foot on brake, throttle and idle until you reach 210 degrees operating.
-Let the car roll under idle for another 5 minutes to ensure everything is up to temp, you can brake but can't use throttle. I drove around my block twice.
-Normal driving get on a highway.
-Drive 55mph for 5-10 minutes before: Accelerate up to 75-80, then coast it down to 20, repeat 3-5 times.
-60mph, decel to 50, repeat 3-5 times.

At this point the O2 sensor should be ready, however they advised not plugging in a tech2 and heading straight to emissions for a test and it passed.

 

[dkad260]

Generally the emissions stations will pass with one parameter not ready. The evap takes the longest, O2 usually a day or 2 max. Hopefully they will pass you with only 1 not ready.

Edit to add: Saw you passed.

 

[t_bergman]

Generally the emissions stations will pass with one parameter not ready. The evap takes the longest, O2 usually a day or 2 max. Hopefully they will pass you with only 1 not ready.

Yes, passed with everything but EVAP not ready; for some reason if anything is pulling data from the ECM is doesn't run tests which is a giant pain.


I do have the L96 engine which may or may not act like the 6.2l or 5.3l for this test.

 

[Fless]

The official evap drive cycle (only on a cold start, with a few other requirements) involves a variety of throttle pulls and deceleration activity; the deceleration events allow high vacuum to test the integrity (sealing) of the complete evap system. A purge and seal test does essentially the same without the ECM actually "documenting" it for the emissions requirement.

 

[Doubeleive]

Needing to get the emissions tested on my '13 Yukon XL 2500 and the EVAP/O2 sensors are showing as not ready, I've already failed once and have 0 DTCs coming alive.

Does anyone have a procedure doc on how to run the evap service bay test with a Tech2Win?

I want to also ensure I am getting into the vehicle correctly when going into the Tech2, if anyone has a guide on the various 1/2 options as I've got a 2500 with the L96.

It doesn't get driven heavily however I've used it as my daily driver since 7/5 when it first failed and in I/M status the EVAP and O2 sensors are still not ready.

if everything is working properly, then it just needs to be driven at 55mph for about 50 miles and a few cold start to fully warmed up drives to get the evap to set

 

[Doubeleive]

The official evap drive cycle (only on a cold start, with a few other requirements) involves a variety of throttle pulls and deceleration activity; the deceleration events allow high vacuum to test the integrity (sealing) of the complete evap system. A purge and seal test does essentially the same without the ECM actually "documenting" it for the emissions requirement.

I believe the gas tank also has to be at a certain level as well, keeping it at around 1/2 tank is a safe bet.

 

[Fless]

I believe the gas tank also has to be at a certain level as well, keeping it at around 1/2 tank is a safe bet.

Correct. The spec is 1/8 to 7/8 full, but as we all know the gauges are sometimes off. A few guides say 1/4 to 3/4; anything in between those values should be good.

Also the ambient temp needs to be within 9 or 11 deg of the engine coolant temp, dead cold start, etc. Lots of variables to consider. Anyone wanting to see the exact conditions needed can do a search here, they've been posted several times.

 

[Doubeleive]

trying to do the service bay evap test is not exactly easy, if you screw it up then you have to wait and try again many hours later....
aside from all the other requirements you have to hold the rpm in a certain range for *** amount of time, one goof up and it's a wash.