How To: Techstream Evap Test (P0442 and P0456)

Wanted to write up a quick how to on how to use Techstream to run an Evap Test and diagnose/confirm repair of a P0442, P0456, or similar evap leak code. As noted in the FSM, if you have other codes than these present simultaneously troubleshoot those first.

Toyota doesn't make things easy troubleshooting these codes. The naming conventions of the different solenoids is different in Techstream, the FSM, and the parts diagrams which makes it all the more confusing (this video was super helpful). For reference I am running V12.20 of Techstream, and my truck is a 2003 2.7L federal emissions. This was the most confusing part to me in understanding how to use Techstream and it's bidirectional capabilities. So I'll break that down first and then get into the specifics. See below:



A P0442 or P0456 indicates a problem in the dotted line in the picture above. The below graph also helps visualize what the ECM is looking for in each code:


In simple terms, the computer pulls the evap system (area in the dotted lines) into a vacuum by 1) opening up the "VSV for Evap". It then 2) closes the "VSV for Evap" (therefore stops applying vacuum) and 3) closes the "VSV for CCV" and monitors 4) how the vacuum decays (approaches 0 mmHg gauge) over time. A P0442 or P0456 means that the pressure goes back to atmospheric too quickly indicating a small or very small leak (in the area in the dotted lines).

Now, onto how to use Techstream to run the evap check.
1. Open Techstream
2. Plug in your VCI cable to your PC and truck
3. Click "Connect to Vehicle" to connect to your vehicle with Techstream
4. Double click "Engine and ECT" under "All ECUs"
5. Click "Utility"
6. Double click "Evaporative System Check"
7. You should now see this window

8. If you are just diagnosing a P0442 or P0456 keep clicking till you get to step 5 (below). Watch the vacuum on the screen and click "Next" once the vacuum get's to between -15 and -20 mmHg. If the vacuum goes below -22 mmHg then vent opens so the system doesn't get damaged and it will keep cycling this way...then you end up with a lot of unnecessary flags that make it harder to find the data you're looking for in the event file. This step is pulling the canister and fuel tank into vacuum.


9. The system is now sealed once you are on step 6. Watch your vacuum decay on the screen and click "Next" once it gets to ~0 mmHg or you get impatient of waiting for it to drop. Try to let it decay for a minute if you can.


10. Go to step 7 which pulls the system into vacuum again and follow the same directions in #8 above...i.e. click "Next" once the vacuum reaches ~-20 mmHg.
11. The system is now sealed and the fuel tank is isolated from the charcoal canister (note the "Tank Bypass VSV" is closed. Since the vapor pressure sensor is located on the fuel sending unit this step is now just testing how well sealed the fuel tank is. Watch your vacuum decay on the screen and click "Next" once it gets to ~0 mmHg or you get impatient of waiting for it to drop. Try to let it decay for a minute if you can.


12. Skip through the rest of the steps and finish the test. Techstream will then prompt you if you want to save the event file, click yes and save it.
13. Finally, let's analyze the data

Techstream Event Files can only be opened in Techstream. There is an option to export them to a .csv which would have made my life way easier, but that function was yielding a blank .csv file for me. If someone knows whether this has been fixed in newer versions or what the trick is, let me know. You can open your event files in Techstream by going file->Open Scan Data File->Open Service Event File->select your file. Expand all the flags within the event file and then you want to navigate to each of the actions above and note the timestamp and vacuum reading.


The flags correlate to each step in the evap test. For example, "Flag 5" is the start of "Step 5" in the evap test where vacuum is applied to the system. Therefore, to get the timestamp and final vacuum reading at the start of the system sealing I need to go to "Flag 6" which corresponds to "Step 6". Make note of the vacuum reading and timestamp:


Now using the same logic write down the timestamps and vacuum for "Flag 7". Save these for later, this is your first test of the air-tightness of the canister and fuel tank combined. Next navigate to "Flag 8" which is the start of "Step 8" where the air-tightness of the fuel tank is tested. Write down the vacuum and time stamp, then go to "Flag 9" and do the same. You have no collected all your data and with a little math can determine what the decay rate of the vacuum is in mmHg/second. Making a little spreadsheet makes this easier if you are making multiple repairs and retesting several times. My results are below:


As you can see, I had a pretty significant leak that appeared during the tank test and tank and canister test. If the results showed the tank test with minimal decay but the canister and tank test with significant decay then logically, there is a leak in the canister assembly or hoses. This test pointed out that my fuel tank was likely the main issue. I will note that I do not know what decay values are acceptable in the eyes of the ECU, I ran this test as a relative test to confirm that my repairs improved the decay rate. Still TBD whether this keeps the CEL off, I will update this thread accordingly.

I'm breaking out the rest of the trouble shooting and repairs into another thread since this writeup is pretty lengthy. Below is a link to all the repairs and diagnosis I did:
https://www.tacomaworld.com/threads/p0442-repair-troubleshooting-log-and-smoke-test.843788/

 

A couple updates on this as my CEL did eventually come back for a P0456 code this time:

"Techstream Event Files can only be opened in Techstream. There is an option to export them to a .csv which would have made my life way easier, but that function was yielding a blank .csv file for me. If someone knows whether this has been fixed in newer versions or what the trick is, let me know. You can open your event files in Techstream by going file->Open Scan Data File->Open Service Event File->select your file. Expand all the flags within the event file and then you want to navigate to each of the actions above and note the timestamp and vacuum reading."

Update: Instead of navigating through the flags and writing down vacuum and time values, I did figure out how to use the graphing function in Techstream thanks to another thread. After opening your event file, simply select your parameter so it's highlighted and then click the graph button on the bottom of the screen:



I used the graph function (you can add time and amplitude rulers by clicking "menu") to measure the decay and it revealed that in some datasets there is a several second lag between the command from Techstream and the ECU actually closing/opening solenoids. This gave me more granular and accurate vacuum decay rates. Here is the progression of results and visually you can really see the difference:

Before any repairs you can see that the decay on the canister and tank leakdown test was ~18mmHg in 10.6 seconds or 1.7 mmHg/sec


After repairing fuel tank and replacing everything else on top of it you can see the fuel tank leakdown (teal rectangle) is looking much better and so is the tank and canister leakdown (red rectangle), but the difference in the two shows that the charcoal canister is still not holding vacuum. The decay for the canister and tank leakdown was 0.34mmHg/sec, a marked improvement but apparently this still wasn't good enough as it threw a P0456.



After all repairs, this is how the decay should look. The canister and tank leakdown was 0.097mmHg/sec. The tank only leakdown was 0.07mmHg/sec, meaning the charcoal canister loses vacuum at about 0.027mmHg/sec. The fuel tank is a very large system with lots of hoses, gaskets and orings that need to seal well so it's expected that it will lose vacuum.


"I will note that I do not know what decay values are acceptable in the eyes of the ECU, I ran this test as a relative test to confirm that my repairs improved the decay rate. Still TBD whether this keeps the CEL off, I will update this thread accordingly."

Update: I can now confidently say that the decay rates shown above are acceptable in the eyes of my ECU since my CEL has turned off, and fingers crossed it stays off.