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Premium Member
2002 Chevrolet TrailBlazer LTZ 4.2L
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114 Posts
Discussion Starter · #1 ·
Good morning,

I have an intermittent P0440 code. The first time it came up was back in November when I got the truck. I had purchased a locking gas cap that I had apparently not completely clicked in place before locking it. Cleared to code, put the cap back on properly and drove on without issue ever since. Fast forward to about a week ago. Code came back. Checked the cap again, cleared the code and drove with no other issues. I drive 50 miles round trip, 5 days a week. Code came back this morning when I get to work.

I'm pretty sure it's not the locking gas cap, but I'm going to put the original back on when I get home from work to test if this is it. I'll run it for about a week and see if the code returns.

I know there is a wealth of knowledge on this site already and have received a lot of amazing help and guidance so far, as well as about 4 or 5 things this could be. Has anyone had experience with this and can direct me to the most likely cause, aside from the gas cap? I'd rather not throw a bunch of evap parts at it if it's something as simple as the cap or a hose.

Appreciate you all and look forward to the help.
 

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Premium Member
2004 chevy trailblazer_lt
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2,347 Posts
Morning! Well, the P0440 can be a royal pain to track down. Please let me refer you to this webpage that discusses many of the common causes of the P0440 code.


You might need to smoke test the EVAP system in order to track the cause down.

Good Luck!
 

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Premium Member
2002 Chevrolet TrailBlazer LTZ 4.2L
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114 Posts
Discussion Starter · #3 · (Edited)
Thank you for this. I was looking at this very site this morning while in the parking lot trying to diagnose the code. I have a better OBDII tool at home that I'll have to check with later.

I should also have mentioned that I do not smell gas fumes and am not sure if I would with this code issue. My fuel economy has stayed at a laughable 13.5 MPG since I got the truck in November. I need tires and an alignment at some point, so I'm dismissing the fuel economy numbers for now.
 

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Premium Member
2004 chevy trailblazer_lt
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2,347 Posts
Great minds definitely think alike! I think the "problem" with tracking this code's cause down is that it is sometimes caused by pinhole or smaller sized holes that are really a pain to find. I know a gent who has a 2002 or 2003 Envoy that threw this code ever month or so. He spend a couple of years trying to isolate the cause and finally, if I recall correctly, he found some rust around the top of the filler tube and that's where the leak was. About the same time, he learned of a "recall" or something where GM was replacing them under an "extended warranty" for that part.

So, be diligent, don't get too bummed out if it becomes a royal pain in the you know what to track down and Good Luck!!
 

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Premium Member
2002 Chevrolet TrailBlazer LTZ 4.2L
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114 Posts
Discussion Starter · #5 ·
Appreciate the feedback and encouragement. I'm thinking of starting at the gas cap end of the truck and slowly working my way up to the front. The filler neck looked ok the last time I was under there to replace the bump stops and a corroded ground strap, although I didn't full on inspect it as it wasn't even a thought. Definitely adding to the summer project list.
 

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Premium Member
2004 chevy trailblazer_lt
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2,347 Posts
Sounds good and good luck!
 

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'05 Chevy TB EXT
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4,051 Posts
Appreciate the feedback and encouragement. I'm thinking of starting at the gas cap end of the truck and slowly working my way up to the front. The filler neck looked ok the last time I was under there to replace the bump stops and a corroded ground strap, although I didn't full on inspect it as it wasn't even a thought. Definitely adding to the summer project list.
tsk, tsk, tsk, Mike .... you are going down the same road of denial that almost every owner travels, seeking angelic intervention or a celestial finger to point to the leak for you.

Sadly, the heavens don't give a fig about vacuum leaks, other than abhorring them.

Google how to build your own smoke generator ---- it's fun, educational and gives one a rosy sense of inner accomplishment to do so.

I made one from an old aquarium air pump, a glass Mason jar w/lid and screw ring, some plastic hospital oxygen hoses (that aren't in use at the time), and a Harbor Fright 30W soldering pencil.
 

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Premium Member
2002 Chevrolet TrailBlazer LTZ 4.2L
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114 Posts
Discussion Starter · #10 · (Edited)
Little update. I replaced the aftermarket locking gas cap with the stock non-locking one on Friday. Made sure to check the sealing ring in the cap for deterioration or cracking. All was good. Drove home, filled the tank with 87 on the way and parked it. Monday morning on the way to work the light came back on. I strongly feel this rules out the gas cap, so I put the locking one back on (to combat fuel pirates).

I also reset the average fuel economy monitor Friday, and as of this morning the fuel economy average jumped from 13.5 to 14.5. I must also note that I spend on average half of my 45 minute commute to work in stop and go traffic and on average 2/3 of my 90 minute commute home in stop and go traffic, so I know for a fact this has an impact on the fuel economy.

I'm going to check the filler neck (hopefully) this weekend (weather permitting), as well as 12 volt bench test the vent and purge valve solenoids to check functionality. If the solenoids both test functional, I will assemble a homemade smoke testing machine and go from there.

Does anyone know how to test the vapor canister for functionality?

Thank you.
 

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Premium Member
2004 chevy trailblazer_lt
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2,347 Posts
If your vapor canister (aka charcoal canister) is working properly, then your fuel trims should not be intermittently rich for many seconds at a time. You have to monitor the short and long term fuel trims (then add them together) to see if this is the case. If the canister is overly saturated with fuel or plugged up, it might cause problems when you fill up with fuel.

FYI - a couple of years back the fuel trims on our 1999 Buick Century showed that the engine was running rich several times an hour for anywhere from 20 - 60 seconds. With Ravalli's guidance I monitored several different engine sensors and ruled out the MAP sensor, the MAF sensor and some other things. What was happening was the charcoal canister had become saturated with gasoline (caused by my topping off the tank at fill ups) and whenever the EVAP system commanded the purge valve to run, it the engine sucked in a lot of fuel vapors from the charcoal canister and it would run rich for a bit. The sum of my Short and Long Term Fuel Trim Values was in the range of -20 to -30. I replaced the canister and the new one was noticeably lighter in weight than the old one (both were OEM GM parts) and my fuel trims straightened out.

Moral of the story, do not top off the gas tank when you fill up!
 
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Good morning,

I have an intermittent P0440 code. The first time it came up was back in November when I got the truck. I had purchased a locking gas cap that I had apparently not completely clicked in place before locking it. Cleared to code, put the cap back on properly and drove on without issue ever since. Fast forward to about a week ago. Code came back. Checked the cap again, cleared the code and drove with no other issues. I drive 50 miles round trip, 5 days a week. Code came back this morning when I get to work.

I'm pretty sure it's not the locking gas cap, but I'm going to put the original back on when I get home from work to test if this is it. I'll run it for about a week and see if the code returns.

I know there is a wealth of knowledge on this site already and have received a lot of amazing help and guidance so far, as well as about 4 or 5 things this could be. Has anyone had experience with this and can direct me to the most likely cause, aside from the gas cap? I'd rather not throw a bunch of evap parts at it if it's something as simple as the cap or a hose.

Appreciate you all and look forward to the help.
They have a cleaner at auto zone for this I had the same issue but the cleaner didn't work for me I used injection cleaner a couple times and my code hasn't came back on since try the cleaner if that doesn't work try the injection cleaner
 

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Good morning,

I have an intermittent P0440 code. The first time it came up was back in November when I got the truck. I had purchased a locking gas cap that I had apparently not completely clicked in place before locking it. Cleared to code, put the cap back on properly and drove on without issue ever since. Fast forward to about a week ago. Code came back. Checked the cap again, cleared the code and drove with no other issues. I drive 50 miles round trip, 5 days a week. Code came back this morning when I get to work.

I'm pretty sure it's not the locking gas cap, but I'm going to put the original back on when I get home from work to test if this is it. I'll run it for about a week and see if the code returns.

I know there is a wealth of knowledge on this site already and have received a lot of amazing help and guidance so far, as well as about 4 or 5 things this could be. Has anyone had experience with this and can direct me to the most likely cause, aside from the gas cap? I'd rather not throw a bunch of evap parts at it if it's something as simple as the cap or a hose.

Appreciate you all and look forward to the help.

fuel pressure sensor? They like to break off and dangle by the connection
 

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2003 olds bravada
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12 Posts
I built a smoke machine for P0440 problem on my Bravada. I never saw any smoke but I was sure I knew there was a crack at the gas tank where the filler tube connects. I used some soapy water and pumped a little air into the tank. I was able to verify where the crack was. I repaired the crack with a soldering iron.
 

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2003 gmc envoy_sle
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177 Posts
My 2003 had a recall, or a TSB on the plastic part of the system just "under" the filler tube. Supposedly the plastic would develop a crack and cause the light to trip.

There also is a metal tube with a 180° bend in it down in the same area. Rust had put a small hole in it.
 

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Premium Member
2002 Chevrolet TrailBlazer LTZ 4.2L
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114 Posts
Discussion Starter · #16 ·
I'm pretty sure I read that same thing about the recall and it being limited to 100,000 miles. I'm at 97,000. Could I get in on this recall or am I out because it's a 20 year old truck? Where would I find out the information on getting this dealt with under the TSB?
 

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2003 gmc envoy_sle
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177 Posts
I'm pretty sure I read that same thing about the recall and it being limited to 100,000 miles. I'm at 97,000. Could I get in on this recall or am I out because it's a 20 year old truck? Where would I find out the information on getting this dealt with under the TSB?
Not likely you could get it fixed under warranty. I couldn't get mine fixed years ago. You would likely have to smoke it to find it anyway.
 

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'05 Chevy TB EXT
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4,051 Posts
I'm pretty sure I read that same thing about the recall and it being limited to 100,000 miles. I'm at 97,000. Could I get in on this recall or am I out because it's a 20 year old truck? Where would I find out the information on getting this dealt with under the TSB?
Contact you local GM dealer .. they are most likely going to have any parts you need without a long wait ... mebbee....
 

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2003 olds bravada
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12 Posts
My 2003 had a recall, or a TSB on the plastic part of the system just "under" the filler tube. Supposedly the plastic would develop a crack and cause the light to trip.

There also is a metal tube with a 180° bend in it down in the same area. Rust had put a small hole in it.
When mine failed it was out of the recall on mileage.
 
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