PO446, proper troubleshoot?

2002 Z-71 Tahoe, 225k miles.

Driving down a lot of dusty dirt roads, this code is common for the clogged evap solenoid, so I replaced it and reset the light.

2 days later, it's back. Upon searching for what's next, I just get a ton of vids "it's this, it's that, no you have to replace this" ect ect.

One clue that may help diagnosis, is that it does not have issues filling up, so I am not sure if this means the charcoal canister is probably ok, or whether it can still be the issue. It also does not smell like gas when idling, (I heard purge valve can cause this??)

The other part that I heard gets killed by dust is the fuel tank pressure sensor on top of the tank.

Anyway, instead of throwing money into a hole until the light goes away, does anyone with more experience with this have any advice on what the next thing to check or replace should be?

Try this website called charm.li

You can search diagnostics procedures for a given code.

Another excellent source of the theory and operation of GM EVAP systems is YT channel. Here's one of the many videos they have on this:
The other thing you need is a birectional scanner where you can manually command EVAP purge solenoid and vent solenoid while you monitor tank pressure. A smoke machine may also be required.

Nice truck BTW

shot gun the 3 parts with OEM and call it a day
run you about $200
aftermarket parts for the evap system typically fail in short order

strutaeng said:

Try this website called charm.li

You can search diagnostics procedures for a given code.

Another excellent source of the theory and operation of GM EVAP systems is YT channel. Here's one of the many videos they have on this:

The other thing you need is a birectional scanner where you can manually command EVAP purge solenoid and vent solenoid while you monitor tank pressure. A smoke machine may also be required.

Nice truck BTW

Click to expand...

Thanks, I'll check out the site!

Doubeleive said:

shot gun the 3 parts with OEM and call it a day
run you about $200
aftermarket parts for the evap system typically fail in short order

Click to expand...

What 3 parts are you suggesting? Purge, solenoid, and pressure sensor, or canister? I think the canister is 200-something itself.
I'm leaning towards it being the pressure sensor, because of the dust, but I hope not, because that apparently means dropping the fuel tank

The pressure sensor can be tested while diagnosing the evap system. Eric O at South Main Auto has a couple of YouTube videos where he uses a scan tool, goes through the diag, and it ends up being the fuel tank pressure sensor, but having that fail is much rarer than having a bad vent valve or purge valve, or another kind of leak.


The GoTech Wells site has quite a few vids on evap; Mike does a great job of explaining how they work.

Fless said:

The pressure sensor can be tested while diagnosing the evap system. Eric O at South Main Auto has a couple of YouTube videos where he uses a scan tool, goes through the diag, and it ends up being the fuel tank pressure sensor, but having that fail is much rarer than having a bad vent valve or purge valve, or another kind of leak.

The GoTech Wells site has quite a few vids on evap; Mike does a great job of explaining how they work.

GoTech

Automotive repair content hosted by ASE Master Certified technicians with a focus on diagnosing and repairing today's problem vehicles with speed and accuracy.

www.youtube.com

Click to expand...

I'll check it out, thanks! The purge valve would be a lot easier to replace, so hopefully that's the cause

88lance said:

What 3 parts are you suggesting? Purge, solenoid, and pressure sensor, or canister? I think the canister is 200-something itself.
I'm leaning towards it being the pressure sensor, because of the dust, but I hope not, because that apparently means dropping the fuel tank

Click to expand...

these 3 pieces and just for good measure a new gas cap, should be around $250 total, maybe a smidge more I have a business account so no tax and usually free shipping.
a diagnostic is half this cost and then usually it's just a guess anyway, the issue is hard to narrow down sometimes.
basically it's a vacuum leak.
the filter for the vent valve should be zip tied way up at the top of the gas fill tube, it's easy to just disconnect the fill tube, grab it and pull it down, zip tie the filter around it stick it back up and re-attach to the body. this keeps dirt and dust to a minimum
replacing everything is pretty easy, drop the spare tire for more room, the clips you just press forward, squeeze and then pull and they should come right off

You can also check these systems with a DVOM. Look at a ECU pinout of the fuel tank pressure sensor. Backprove and monitor the voltage with a DVOM while opening the gas tank or manually opening the purge/vent solenoid.

Buy yourself a 20' set of jumper leads and hook up to your battery, then open the purge or vent solenoid by jumping them with the leads.

Additionally, the purge solenoid you can also check for leaks with a hand pump vacuum. Again, apply 12 VDC to the terminal and you'll the vacuum goes to zero. It should hold vacuum too.

It's the hard way if checking w/o a birectional scanner, but accomplishes the same thing.