GLKustoms

I keep getting the P0446 evap/emission code on my 05' Suburban. I've changed the vent solenoid near the fuel tank and the purge valve on the intake. I don't see and kinks in the lines and the old parts that were replaced were not really dirty and tested good. Any ideas on what else can cause this?

tech2

what the system is doing when its runs this test is testing for a cleared evap path.
it does this by watching for a pressure drop measured by the ftp sensor. the vent solenoid is closed, the purge solenoid opened allowing intake vacuum to created a drop in pressure. the sensor is not seeing the drop in pressure for a number of possible reasons and sets the dtc.

to created the drop in vacuum. the system must seal/not leak and the lines, canister be clear of debris




one possibility is the ftp sensor is bad. are you getting a p0451 which is a dtc for the ftp sensor?

without a scan tool and evap smoke tester you are left to the guessing game. If that is the case; and you are not having and slow fuel filling issues...try a new ftps.
you can remove it without lowering the tank but its tight. lowering the tank a couple inches makes it easy.

cleveland63b

have the codes been cleared since you replaced the parts? it can take quite a while to get all the evap monitors to run if you don't have a scanner to clear the codes.

GLKustoms

I bought the truck used in July. The check engine light was a hidden easter egg that didn't show up until August (after the first payment). 4 out of 5 drive cycles, I get the P0446 code. 1 out of 5 drive cycles, I get the P0496 code. I read and reset the computer with a ScanGaugeII. It hasn't given me both codes at the same time though. I bench tested the old purge and vent valve and they still clicked open/shut. Neither the vent or purge valves were clogged or even dirty, I just changed them first since they were so cheap (About $15 each/ACDelco). None of the evap lines look damaged or corroded upon visual inspection. The gas cap looks ok, but I may replace or change to an ACDelco locking cap anyway. I'm not smelling gas in the truck or having slow fuel filling issues like I've read some people had with the P0446 code. I'm not looking forward to dealing with the ftps. Soon, I will have an completely new evap system, smh.

tech2

jeazzz parts are cheap in the states $15!!!!!!!!!!!! We get hammered in Canada.

GLKustoms

If available, I get all of my parts from Amazon.com or RockAuto.com. These came from Amazon. They have the cheapest prices. Parts are high locally here too! Had the dealer where I bought it from do a smoke test. Tech said the leak is so small that they cannot see it. Said since I changed the two valves already, it has to be the fuel cap, fuel tank pressure sensor, or charcoal canister that's throwing the code. Well, that's all the parts left in the system, common sense, smdh. I was hoping they would have pinpointed it. Cost $95 for them to diagnose nothing basically. Currently on Amazon, a new canister is $105, non-locking OEM cap $18, and fuel tank pressure sensor $14. Could have saved time/money if I would have just changed everything myself while the weather was still warm and I was off from work. If it's not the cap, I will have to wait until it warms up some to change the ftps or canister! Thanks for your input though.

cleveland63b

if its big enough to be detected by the ecm then its big enough to show up on a flow and/or smoke test IF theres actually a leak.

tech2

sorry to hear that.
did they note a change in the ftp sensor when the smoke tester was filling the system? did the sensor rear 0mmhg when the tank cap is removed? this would at least tell you the ftp is seeing a pressure change?

no fault founds in good dealerships must be accessed by the shop foreman first...to ensure the tech did not miss anything. Sometimes its all about the truck going to the right tech. No one can fix everything but that is when you ask for help.


wait for spring and do it yourself...it will not create a drivability problem.

GLKustoms

I think they are just lazy and trying to get me out of there. I'm tired of dealing with them also, is there a cheap way I can test the ftp sensor myself? I've changed the fuel cap now and it's still throwing the P0446 code.

jbr4dsher

Having the exact same issues with 2008 Tahoe. Almost a year ago the P0449 code was being thrown and I had problems getting fuel into the tank which ended up being the purge valve. Everything was great for a few months, then the computer started throwing the damned P0446... so far I have changed out the gas cap and the vent solenoid just like you with no luck.

Guess the next cheapest option is to try and replace the ftps... sure wish I knew someone with a big lift to get the truck elevated. Guess I'll buy a couple of those ramps you see at autozone :/