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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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Discussion Starter #1
The problems: My 02 TB ls model is always in closed loop. I have the p0420 and P0440. After I replaced the rear o2 due to p0137 code I got P0420 after a 30 minute drive. I replaced the front o2 both with Walker brand but I do have a smelly exhaust.

can you help? Any thought and or ideas to finally get the check engine light off with a fix?

Still having full power with no lags, occasional rough idle but once fully heat soaked truck is super smooth and quiet. Tried cataclean with a tank of gas twice actually and it did cut that stinky exhaust smell by 90% but no fix.

Things I changed in 2020: both o2 sensor's by Walker, VVT solenoid, Crank position sensor, even that evap canister of some sort that's underneath the spare tire for the heck of it.
 

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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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Discussion Starter #2
Bit of an update, today I was collecting data with the HpTuners and the Cat seems to be working as it is getting to 1100 degrees but I heard a slight rattle and is possible its partially broken. Only reason I found that out is because I let the passenger window all the way down, yes all this time i havent done this because of the smell.

Also while the car was on idle I was trying to locate that bad exhaust smell and its not from the tail pipe as I even placed my hand on it for the smell test. I narrowed it around it around the cat either the front of the rear. Somewhat seems like the gasket has failed or could be a broken weld or even a pinhole.
 

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2004 chevy trailblazer_lt
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Well, it sounds like you have found the problem for the P0420 OBDII code - the apparently broken catalyst inside the catalytic convertor.

The P0440 is an EVAP Emissions system code. You likely have an air/vacuum leak somewhere in the fuel emissions system.. I know there were problems with cracks and rusting in the filler neck with the 2002 TrailBlazers/Envoys.

You could have a cracked emissions line, a defective EVAP Purge Valve Solenoid, a defective EVAP Vent Valve, a broken charcoal canister, a broken wire to either the purge valve solenoid or vent valve, a plugged emissions line, a rusting out metal top on the fuel pump assembly, etc. Hence the need to diagnose the problem. One way is to rule out leaks through the use of a smoke generator connected to the EVAP port (covered with a green colored cap) in the engine bay. The smoke generator fills the EVAP and fuel system with smoke at a very low pressure (1 -2 psi) and then you look for where the smoke is leaking from.
 
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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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Discussion Starter #4
Well, it sounds like you have found the problem for the P0420 OBDII code - the apparently broken catalyst inside the catalytic convertor.

The P0440 is an EVAP Emissions system code. You likely have an air/vacuum leak somewhere in the fuel emissions system.. I know there were problems with cracks and rusting in the filler neck with the 2002 TrailBlazers/Envoys.

You could have a cracked emissions line, a defective EVAP Purge Valve Solenoid, a defective EVAP Vent Valve, a broken charcoal canister, a broken wire to either the purge valve solenoid or vent valve, a plugged emissions line, a rusting out metal top on the fuel pump assembly, etc. Hence the need to diagnose the problem. One way is to rule out leaks through the use of a smoke generator connected to the EVAP port (covered with a green colored cap) in the engine bay. The smoke generator fills the EVAP and fuel system with smoke at a very low pressure (1 -2 psi) and then you look for where the smoke is leaking from.
Brief update for finding an exhaust leak, no luck with the soapy water method. I somewhat feel some air coming from the catalytic converter to muffler flange, but had to stop the test as I needed to leave.

I did change the fuel cap as it was cracked badly and that was the first thing I did when I got the p0440 code. I will need to search for a diagram for all the emission lines going to the engine, not sure what's what and still learning these inline 6.

Will report back tomorrow hopefully with new info.
 

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Good luck with finding the exhaust leak.

Attached are diagrams of the Emissions Hose Routing (primarily in the engine compartment), and the EVAP Emissions Hose Routing (primarily by the gas tank). Note, the EVAP Purge Valve Solenoid is located in the engine compartment on the driver's side of the engine block about halfway down from the top and about 18 inches or so behind the alternator.

As always, good luck!
 

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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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Discussion Starter #6
Good luck with finding the exhaust leak.

Attached are diagrams of the Emissions Hose Routing (primarily in the engine compartment), and the EVAP Emissions Hose Routing (primarily by the gas tank). Note, the EVAP Purge Valve Solenoid is located in the engine compartment on the driver's side of the engine block about halfway down from the top and about 18 inches or so behind the alternator.

As always, good luck!
WOW thank you for your help and these diagrams!

Will inspect these areas on the Trailblazer within the next few days and I will report back!
 

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You are quite welcome!

Again, good luck!
 

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Gas cap, neck of gasoline filler tube (just below were it attaches to body), dirty EVAP canister vent valve (they have a tendency to become clogged with dirt and stick open), EVAP Purge calve (housings crack, valve inside fails to close completely, are the most common ones I can think of right at the moment.

You can test the vent and purge valves by removing them and seeing if you can blow through them energized and not energized (apply 12 VDC using test leads after removing them from the vehicle. IF your TrailBlazer has lived most of it's life in the country with lots of dirt and gravel roads, then it is very likely the canister vent valve and charcoal canister are jam packed full of dust and in need of replacement.
 

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use of a smoke generator connected to the EVAP port (covered with a green colored cap) in the engine bay. The smoke generator fills the EVAP and fuel system with smoke at a very low pressure (1 -2 psi) and then you look for where the smoke is leaking from.
That's what I was going to suggest as well. I've also seen some use a shop vac to pressurize the exhaust system on YouTube. Never tried this method myself.
 

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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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Discussion Starter #11
That's what I was going to suggest as well. I've also seen some use a shop vac to pressurize the exhaust system on YouTube. Never tried this method myself.
Hello and I did try the shop vac method with soapy water. Although I could not pin point the faulty area, I could smell the remnants of the exhaust for a moment.
 

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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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Discussion Starter #12
Gas cap, neck of gasoline filler tube (just below were it attaches to body), dirty EVAP canister vent valve (they have a tendency to become clogged with dirt and stick open), EVAP Purge calve (housings crack, valve inside fails to close completely, are the most common ones I can think of right at the moment.

You can test the vent and purge valves by removing them and seeing if you can blow through them energized and not energized (apply 12 VDC using test leads after removing them from the vehicle. IF your TrailBlazer has lived most of it's life in the country with lots of dirt and gravel roads, then it is very likely the canister vent valve and charcoal canister are jam packed full of dust and in need of replacement.
Gas cap has been changed when I first got that evap code. One thing I must add is when I try to put gas in, there's been plenty of times i have to raise the nozzle and push in just to pump gas. Otherwise will click and nothing will pump but I don't smell or have any raw gas leaks as that will be obvious. Could that symptom potentially be the culprit?

I've seen on YouTube someone with a hole in the filler neck still pumping gas and loosing some of it. Lol
 

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Hello and I did try the shop vac method with soapy water. Although I could not pin point the faulty area, I could smell the remnants of the exhaust for a moment.
Yeah I don't know what I was thinking. Somewhere I saw something about an exhaust flange leak, but maybe I was reading two different forums at once.

Pressurizing the exhaust pipe is not going to test the EVAP system. Do what chem_man has suggested above and smoke the EVAP system.
 

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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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Discussion Starter #14
Yeah I don't know what I was thinking. Somewhere I saw something about an exhaust flange leak, but maybe I was reading two different forums at once.

Pressurizing the exhaust pipe is not going to test the EVAP system. Do what chem_man has suggested above and smoke the EVAP system.
Evap and exhaust yes are 2 different things. Umm I think you had said about pressurizing the exhaust with a shop vac which I did try and no luck on that leak.

Far as the evap, well I got under the truck and in front of the gas tank facing the engine, I visually inspected and seen nothing wrong. Idk what that giant canister is called but it's big.

Bare in mind I failed to mention when i pump gas, the gas nozzle unclickes every like few cents and I have to press the gas nozzle firmly and lift upward.
 

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Bare in mind I failed to mention when i pump gas, the gas nozzle unclickes every like few cents and I have to press the gas nozzle firmly and lift upward.
Yeah, like I said... momentary lapse of reason there.

This is a common sign of an obstructed vent tube, stuck vent solenoid, or saturated charcoal canister. I've also experienced this at certain stations that have the pumps turned up really high.
 

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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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Discussion Starter #16
So I'm a bit lost here and confused even with these diagrams.

Are there 3 evap/emission solenoids? I know the engine has 1, under the spare is another, and that giant canister next to the fuel filter is another? Are there any more?
 

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So I'm a bit lost here and confused even with these diagrams.

Are there 3 evap/emission solenoids? I know the engine has 1, under the spare is another, and that giant canister next to the fuel filter is another? Are there any more?
Er... no. What are you identifying as a third solenoid?

#6 is your vent solenoid... near the spare tire.
Near that is the giant canister. That's #2 in the diagram.
Then #1. That's your purge. The one on the engine near the intake.
 

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2002 Pewter ls with automatic trans. 4x2, gray cloth interior.
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Discussion Starter #18
Er... no. What are you identifying as a third solenoid?

#6 is your vent solenoid... near the spare tire.
Near that is the giant canister. That's #2 in the diagram.
Then #1. That's your purge. The one on the engine near the intake.
I replaced a solenoid of some sort that is under the spare tire. Well I needed to take the spare out in order to change it. so #6 the evap vent canister would be in front of the gas tank?

Please excuse my stupidity in all this, I been overwhelmed trying to locate all this and fix it once and for all, especially that awful exhaust leak.
 

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What you replaced under the spare tire is item #6, the EVAP Vent Solenoid.
 
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