P0440 and U1000

littleblazer

Original poster
Member
Jul 6, 2014
9,265
So I have been reading around on the site before posting this up. At the moment I am more concerned with the p0440 than the u1000 since the u1000 passed every drive cycle since it set. The p0440 is kind of an interesting story. Last week I had posted in @Mooseman thread about the evap test on the truck. The code set the day after it was filled while it was idling in the driveway. Next morning I did a drive cycle and the light immediately went out and was good all week. It came back yesterday morning when my father left his mothers house. It is literally a straight shot onto the highway from there so it makes sense that it ran. He filled the truck up the day prior. Now what I was told was the truck always has a slight fuel smell when you fill it. I have checked numerous times and cannot find a leak anywhere. So I run the purge and seal with the tech 2 and it seems fine. Then for comparison I do the same on my truck and it behaves the same. So I am not seeing a real easy issue here. First thing I did was swap the gas caps between the two, my gas cap is brand new as of July so that rules that out as he has had it on since the code set the first time. Tank pressure sensor on his truck is my old one, when we purchased the truck it had the same issue and that ended up being the fix, my truck received the new one but both read. The purge and vent solenoids work as they should as well.

Now the first thing I would start say is that when I was pulling the evap lines off when it set when we bought it, there was charcoal from the canister in the lines. I do not believe this is causing the fuel smell at fill up but is it possible fuel is sloshing into the canister and causing the code to set? From my reading that along with the vent on top and the fuel pump plate itself are the only things left to check and then I should recheck for leaks as well. I know the canister is on borrowed time so that has to be replaced but do you think that could be the sole cause of all this, I do not think it is.

Vehicle info:
2002 envoy 4wd
140k miles
4.2l i6
New purge valve, vent valve, and new used tank pressure sensor
 

xavierny25

Member
Mar 16, 2014
6,323
Staten Island, N.Y
I know the canister is on borrowed time so that has to be replaced but do you think that could be the sole cause of all this, I do not think it is.

:yes:

What brand purge and vent valve did you get?
 

littleblazer

Original poster
Member
Jul 6, 2014
9,265
:yes:

What brand purge and vent valve did you get?
Delco or the top advance part. Whatever they had. The old parts still worked but that was parts throwing before I had the tech 2 lol.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
there was charcoal from the canister in the lines

This is an important clue which basically points to a failed charcoal canister. May have also damaged the valves if there is charcoal in them.
 
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littleblazer

Original poster
Member
Jul 6, 2014
9,265
This is an important clue which basically points to a failed charcoal canister. May have also damaged the valves if there is charcoal in them.
I just find it weird it does a pass/fail. You would think it would throw the specific code for the valve if it doesn't work right. I know the Sierra did. I'll pick up a canister then run some low pressure air through the evap lines to clear out any charcoal then go from there. Good enough plan?
 

Robbiec16

Member
Dec 11, 2015
7
Florida
I too have been facing the p0440 code and I don't know how to attack it. Ive replaced the fuel cap twice so that pretty much rules that out. Im not real sure how to troubleshoot it. Where should I start and with what after the fuel cap. I also can smell fuel but have found no leak around the tank or filler neck.
 

littleblazer

Original poster
Member
Jul 6, 2014
9,265
Pressure sensor, vapor canister, purge valves all come to mind. Truck did it a couple of other times but stopped eventually.
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,642
Tampa Bay Area
FWIW… These suggestions may help to run down the source of the problem:

P0440 Evaporative emission control system malfunction
P0443 Evaporative emission Purge control circuit

These conditions can be caused by a Faulty Purge Control Circuit. There are two possible reasons for these malfunctions:

(1) The FTP (Fuel Tank Pressure) Sensor is NOT reporting the true fuel tank pressure/vacuum condition.

(2) The Fuel Tank Filler Hose may have a small leak or hose fracture somewhere along its length... small enough to allow the escape of pressurized fuel vapors... but not large enough for liquid fuel to accumulate and show... as the bulk of the fuel is always well below the entire length of the hose with short periods of exposure of liquid fuel during filling... or the Fuel Cap is faulty.

Check the Purge for its vacuum connections … as a Disconnected Vacuum Hose or a Leak there will cause P0443 and P0440 error codes to post.

This Generic Evap System Diagram is for viewing the general layout of the sub-components and hosing to prompt other places to investigate for leaks:
 

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