[BowDownBowser]

I have an 07 sierra (Not Classic) with a 5.3L with around 68k miles. I am getting the P0446 code. I tried to blow out the vapor solenoid valve with air and after that I couldn't even fill my tank because it wouldnt vent at all. I replaced the solenoid valve and drove about 200 miles and the code came back. Cleared it and now I'm right around 200 miles again, and it hasn't come back, but the EVAP monitoring cycle hasn't been completed yet according to my scanner. I've read a bunch of other threads on the topic with people saying stuff like replace the canister or replace the tank pressure sensor, but I don't want to be throwing money at it if the code comes back. What is the next step? Is there a way to test the pressure sensor or cansiter? Also if it were the pressure sensor wouldn't I get other codes like the P0453? Thanks in advance for any help .

 

[GMT604]

Next step is getting a scantool on it and testing the FTP Sensor. It won't always set any other codes. Have a look at this video for an explanation, it's for a different GM vehicle but the process is the same.

 

[BowDownBowser]

So Here's an update...
This issue has taught me a lot about my truck as well as the OBD Scanner I have.
I use one of the cheap ELM327 wifi adapters and an Iphone App called iOBD2.
After reading tons of posts in different forums and taking the advice from GMT604 I went in and found on the app where it says EVAP System Vapor Pressure(which is apparently the same as fuel tank pressure) and Commanded Evaporative Purge.
When I initially looked at the Evap System Vapor pressure it read at 12280.50 Pa all the time and the Commanded Evaporative Purge was always 0%
I went to Autozone and picked up a replacement fuel tank pressure sensor and headed to the navy base close by to use their auto skills center.
When I got there I was hoping to use their OBD Scanner to verify everything and actually be able to manipulate the EVAP system, but of course it was broken so I took a shot at understanding what I was getting from my code reader and replaced the fuel tank pressure sensor. Once replaced I was actually getting changing pressure and the commanded evaporative purge was changing as well. At idle I sit around 50 Pa and under a load it goes up to around 16k Pa. I'm hoping that this has resolved my problem, but now I just have to wait for the evap cycle to complete. Hopefully this will help some other people too since the service bulletin for this code can be misleading.

 

[djlove]

Nice job, I completely destroyed one of those sensors dropping a full gas tank by myself on my envoy, if im not mistaken the price tag isn't all that bad right?

Feels good when you can use that little adapter and get really confident in a solution and it ends up fixing the problem.

 

[BowDownBowser]

Nice job, I completely destroyed one of those sensors dropping a full gas tank by myself on my envoy, if im not mistaken the price tag isn't all that bad right?

Feels good when you can use that little adapter and get really confident in a solution and it ends up fixing the problem.

Yeah I had to drop the tank with it about 1/2 full but was able to use a lift and a fuel tank jack and only had to drop it about 3 inches to get to the sensor. Only costs $39.99 at autozone so not too bad. Now I'm just hoping to get through the evap cycle without anything else happening haha. That wifi OBD adapter was definitely worth the $20 I paid with how much it has saved me from having to have someone else diagnose problems.

 

[GMT604]

I believe you have fixed your problem, good job on using your ELM327 and app.

Too many people forget that the FTP Sensor is the only feedback to the PCM for EVAP purge and leak codes. It's the first sensor to look at if you have a tool capable of viewing the data. Yours was a mile off, sometimes it's not so obvious.

 

[chevra]

Well this is interesting. My dads truck seems to be doing the same thing and we have been trying to figure it out for a while. I will have to see if our scanner can read the fuel tank pressure or not.

 

[BowDownBowser]

Well this is interesting. My dads truck seems to be doing the same thing and we have been trying to figure it out for a while. I will have to see if our scanner can read the fuel tank pressure or not.

What type of scanner are you using? If you use an elm 327 adapter you can find an app to show it. Torque for android and iOBD2 for iphone will show it, but it may be labeled as evap pressure. The scan tools that you can buy at autozone to read and clear codes generally wont do anything more than that unless you get into the larger console ones that cost a decent amount. Definitely recommend finding a way to read that though before you do what I did, break and spend $80 on a part not needed just to spend another $40 on the correct one.

 

[chevra]

Well this is interesting. My dads truck seems to be doing the same thing and we have been trying to figure it out for a while. I will have to see if our scanner can read the fuel tank pressure or not.

What type of scanner are you using? If you use an elm 327 adapter you can find an app to show it. Torque for android and iOBD2 for iphone will show it, but it may be labeled as evap pressure. The scan tools that you can buy at autozone to read and clear codes generally wont do anything more than that unless you get into the larger console ones that cost a decent amount. Definitely recommend finding a way to read that though before you do what I did, break and spend $80 on a part not needed just to spend another $40 on the correct one.

My dad just has a blue OBD2 scanner he got from Canadian Tire, I have no idea what brand it is but I did see that it has a section for real time data that I haven't looked into. I also have a DiabloSport programmer which displays a lot of real time data. So I should be looking for either fuel tank pressure or evap pressure. Anything else that it might be called?

 

[BowDownBowser]

Those are the only things I've seen it as, but if it shows real time data then you should definitely be able to see it.