Torque app question / Evap code help (P0446)

[Kaz26]

Vehicle: 2003 Chevy Tahoe 1500 LT (with 5.3L V8)

I understand that Code P0446 means the car's computer has detected a problem with the EVAP system vent valve.

I have tested the evap system vent valve. It is open when not activated and closed (holds vacuum) when activated with a 12v supply.

I cleared the code, but it popped back up. Then I got an ELM327 and used Torque Pro to look at the fuel tank pressure (FTP) sensor value. However, it showed: No Data.

My question: why this is showing No Data? I was under the assumption that the FTP sensor was probably bad so I replaced it. After replacing it, I tried to read it again with the Torque app, but it still says the same thing, "No Data". I also checked the wiring harness to make sure it was getting the 5v that it needs and it is.

Help with this will be greatly appreciated as I cannot smog the car until I sort this out.

Thanks in advance

 

[Fless]

I don't believe that the Torque Pro PID for fuel tank pressure works (as you've discovered) for the NBS so you'll need a different scan tool. I have a Tech 2 that reads it. One needs a bidirectional scan tool to diagnose these evap systems.

Did you by chance confirm that the ECM is able to command the vent valve closed; if not, I suggest testing with a low current test light to confirm that the 12v is being switched on when the ignition is turned on.

Since it's a "performance" issue, it could have a clogged evap canister or one that has plugged evap lines with charcoal pellets. Or something else.

 

[Nooj]

Have you gotten your evap problem resolved?
I’ve been driving my project ‘burb around, waiting on the emission monitors to get to “complete” and I had the P0446 code pop up today.

I also do not have a diagnostic tool capable of reading the fuel tank pressure. But perhaps the voltage can be read with a multi meter, to determine if the sensor is functioning, given the evap valve is functioning. I believe I’ll start sucking or blowing on some hoses tomorrow and see what kinda results I get.

@Fless thanks for sharing the awesome videos, btw! I think those will be a big help.

Nooj

 

[MassHoe04]

Evap. systems seem to be so way over-engineered for what they need to do.

I was getting P0449 ("Evap. System Vent Solenoid Control Circuit") and the "tighten gas cap" message on the DIC. I blew that issue off long enough until I stopped getting that code and started getting P0496 ("Evap. System High Purge Flow").

In my case, I tested the purge solenoid and it was no response. Probably sticking when the vent and gas cap messages were happening and stuck open when the purge unit finally gave up the ghost.

My fix for what first looked like vent issues ended up being replacement of the purge solenoid. Was $20 and I didn't have to do anything with the vent, vent lines or drop the tank!

I have been running code free ever since (a month ago so far) and no tighten gas cap messages either.

May not help you directly. I just wanted to let you know what happened to me and that the two ends of the Evap. system can mislead the diagnosis a little.

 

[Fless]

Evap. systems seem to be so way over-engineered for what they need to do.

I was getting P0449 ("Evap. System Vent Solenoid Control Circuit") and the "tighten gas cap" message on the DIC. I blew that issue off long enough until I stopped getting that code and started getting P0496 ("Evap. System High Purge Flow").

In my case, I tested the purge solenoid and it was no response. Probably sticking when the vent and gas cap messages were happening and stuck open when the purge unit finally gave up the ghost.

My fix for what first looked like vent issues ended up being replacement of the purge solenoid. Was $20 and I didn't have to do anything with the vent, vent lines or drop the tank!

I have been running code free ever since (a month ago so far) and no tighten gas cap messages either.

May not help you directly. I just wanted to let you know what happened to me and that the two ends of the Evap. system can mislead the diagnosis a little.

You're fortunate that the canister didn't go bad and send charcoal pellets all the way up to the purge valve and cause it to stay open, 'cause then you'd have some work ahead of you!

 

[OR VietVet]

In my build thread, you will see when I decided to replace the fuel pump on my rig before the inevitable happened, because I knew that I had a long trip ahead of me in the coming months. Because I have seen many threads here about intermittent and hair pulling problems for the evap systems on these rigs, I just bit the bullet and replaced the whole system with new, including the gas cap. I did not have problems before this and had absolutely none since then. I think @MassHoe04 says it best, "way over engineered".

 

[Fless]

Technically speaking the evap systems are relatively simple. When I had issues with mine I educated myself on how they (should) work and why certain tests happen when they do. Just regular system pressure tests and opening valves to reburn vapors when the time is right.

No matter how you view it, good or bad, it's all about keeping evap fumes out of the air. People think the air is so polluted these days, they should have been around before cars had emissions systems on them. Night and day. Get behind a pre-1970 car today, take a breath, and that's what it all was like.

 

[OR VietVet]

Technically speaking the evap systems are relatively simple. When I had issues with mine I educated myself on how they (should) work and why certain tests happen when they do. Just regular system pressure tests and opening valves to reburn vapors when the time is right.

No matter how you view it, good or bad, it's all about keeping evap fumes out of the air. People think the air is so polluted these days, they should have been around before cars had emissions systems on them. Night and day. Get behind a pre-1970 car today, take a breath, and that's what it all was like.

How 'bout them "air pumps", huh!!!!! With the lines running to the exhaust manifolds......nnniiiiiiiicccccccee!

 

[Fless]

How 'bout them "air pumps", huh!!!!! With the lines running to the exhaust manifolds......nnniiiiiiiicccccccee!

I'll take this system over that one!

 

[OR VietVet]

I'll take this system over that one!

Me too, any day...