P0442 Repair/Troubleshooting Log and Smoke Test

One of the most frustrating codes to diagnose is an evap code on a Toyota. I have been fighting an on and off P0442 on my 2003 2.7L for 2 years now and there is a notable lack of information online on how to properly troubleshoot these codes. Inspection is coming up so I needed to get around to fixing it. I first ran an Evap Test in Techstream and confirmed that the system does not hold vacuum well at all (this is relative) and is leaking from the tank or charcoal canister.



First things first I opened up the FSM to the P0442 diag guide (attached). Following the steps in here:
1. Check gas cap - oring was cracked, more on that later
2. Check filler neck - it was 20+ years old so it had seen better days, decided to replace it since most of the hose fitting were severely corroded where the hose meets the nipple.
3. Check "VSV for Evap" operation - this is located in the engine bay on my truck and is connected to the intake manifold. It's helpful to have Techstream or a bidirectional scan tool that allows you to actuate these solenoids.
3a. I confirmed that mine pulled a vacuum on my finger when energized
3b. De-energize the solenoid (normally closed) and test that air does not flow through it using a handheld vacuum gauge. I used a pop-off test rig for two stroke carbs and a bike pump. Don't apply more than 0.5psi of ~-22mmHg.
4. Check "VSV for CCV" - this is located in the engine bay on my truck and is a vent to the airbox that allows fresh air into the system during a purge condition
4a. Energize the valve and blow air though it. Mine passed using blowing with my mouth. However when I hooked up my pressure tester and put about 0.5 psi in, it could not hold the pressure for more than a few seconds. This is my first potential point of failure as this valve is energized and closed when the ECU checks that the system can hold vacuum
4b. De-energize the valve and confirm that air flows freely. No issues here
5. Check "VSV for Pressure Switching" - located under the bed on the charcoal canister in my truck. Pulled the bed to test it.
5a. Energize the valve and confirm that air flows freely. No issues here.
5b. De-energize the valve and test that it holds pressure/vacuum. No issues here.
6. If all your solenoids test good then that means you're screwed and you're gonna have a really fun time finding the leak. Insert smoke test.
7. Easiest way to find a leak in the evap system is to smoke test it from a few different points. I used this

$66 Solary Automotive Smoke Machine Leak Detector - 12V DC EVAP Vacuum Diagnostic Tester for Pipe System

smoke tester and honestly it works great, however, I would recommend getting a pressure regulator for it so you don't over pressurize the system and damage the very fragile check valves and diaphragms.
7a. Remove both outgoing vacuum lines from the "VSV for CCV" and "VSV for Evap" in the engine bay. the air drain line highlighted below:

7b. one line and apply smoke through the other. Crawl around and look for any smoke.
7c. Now do the reverse and crawl around again and look for any smoke. I had the tiniest bit of smoke coming out of the gas cap so I replaced that.
7d. Clamp off both of the lines in the engine bay that you unhooked and move your smoke tester to the back of the truck. Remove the highlighted hose and connect your smoke tester here:

7e. This is now going to put smoke primarily into the fuel tank so look for any smoke coming out around any of the valves on top of the tank, around the fuel sender, or from the gas cap. I could not see any smoke coming out from anywhere, but the rusty state of my tank led me to dig a bit deeper into it. This more or less concludes the smoke test, I thought pressure testing the tank with a bike pump was a more useful test.
8. If you can't find any leaks with the smoke machine (it can be tricky and you need zero wind or draft), then use a bike pump and pressure gauge to pressurize the tank to 1psi or so through the same highlighted hose above with the large air drain hose clamped off. Important to note that it is a large volume of air in the system so you may not be able to actually build pressure with a bike pump, but it will still work. Look up how to make a 2 stroke pop-off tester, works great for this application too. Once the tank is pressurized spray windex all over the top of it, paying close attention to the fuel sender and other valves. Hit your hose connections and everything too. This revealed leaking all the way around my fuel sender and pinholes in a couple spots on top of the tank.
9. For good measure, pull off the charcoal canister and bench test it following the attached procedure "insp.pdf". Start at Step 8 as you will have done most of this already, but it's good to run through this whole guide and repeat all these steps, there's a little more detail in here than in the P0442 troubleshooting guide. The bench test didn't reveal any obvious problems so I put the charcoal canister back on.

This is a pretty all encompassing guide to test a Toyota evap system and I hope it helps someone else out. In conclusion all this testing revealed 3 different problems: bad gas cap, bad "VSV for CCV", corroded fuel tank. An expensive repair bill... I want to note the importance of going through the entire troubleshooting procedures, if I had just jumped right to the smoke test or if I took a shotgun approach and replaced the charcoal canister I would have missed the bad solenoid and leaking fuel tank and my issue may have persisted. This is why evap codes can be so frustrating and need to be properly diagnosed.

Make sure to recheck everything after repairs either by repeating these tests or running a Techstream (or similar scantool) evap test to confirm your repairs improved the vacuum decay of the system. Turned out I was still leaking around the fuel sender cause the fuel sender was a bit warped from previously being overtorqued. A healthy coating of Permatex Permshield or Hylomar Blue solved this issue. Now I need to complete the drivecycles, I'll update this thread if the CEL comes back on.

 

EDIT: After running the evap monitors after all these fixes I got a P0456 (very small leak). After some further troubleshooting of the charcoal canister and messing around in Techstream (refer to my other thread for more on this) I determined that this was the culprit. That also explained many of the weird issues I was having on hot days and the pump turning off prematurely when getting gas. Dorman unit from 7 years ago has a limited lifetime warranty so I got a new one for free and replaced that. Evap monitor cleared today with no pending codes and no CEL.