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EVAP/Cat CODE Failing inspection... help!

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Old 12-08-2009, 03:34 PM   #1
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EVAP/Cat CODE Failing inspection... help!

Hello:

Ive got a 2001 2door 2wd 5speed Blazer with a little over 78,000 miles...its actually for sale but in order for me to sell it, it needs to pass inspection.

I need some help... the truck sat all summer (winter use only vehicle) and when it started a month or so ago the check Engine light came on. I used a scanner thing and got the light to go off.

Inspection time comes and it keeps failing inspection. Machines are telling me about a cat system not completed as well as evap system not completed.

The shops and the guys i know say i just have to drive it...

What do I need to do? replace vacuum lines? where are they and how difficult or expensive is this?

Any help is much appreciated.

Paul
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Old 12-08-2009, 05:13 PM   #2
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Re: EVAP/Cat CODE Failing inspection... help!

has the SES light come back on? if so what codes(s)
what was the original code?

is it failing because of actual codes, or just the readiness
monitors being "not ready"?

monitors showing "not ready" dont necessarily indicate
faulty parts, just that the component tests havent completed.
this can often be due to test conditions not being met while driving.
Old 12-08-2009, 09:15 PM   #3
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Re: EVAP/Cat CODE Failing inspection... help!

Drive it about 50 miles and see, if there is a code thrown then check it out if no codes take to for inspection. I takes about 50 miles for the monitors to be ready. Make sure the codes are reset before you drive it for 50 miles.
Old 12-09-2009, 12:35 AM   #4
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Re: EVAP/Cat CODE Failing inspection... help!

SES light is back on.

It always says "not completed"

Ive been driving it for a few weeks....still nothing

What are these conditions i have to drive it under? Like what are the exact steps...Reset codes...then do what?

Thanks alot.

Im about ready to kill this thing haha
Old 12-09-2009, 10:31 AM   #5
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Re: EVAP/Cat CODE Failing inspection... help!

first, you need to find out what the exact code is.

next, resist the urge to "clear" the codes.
thats right, dont clear it....
once the problem causing the code is fixed, the light will soon
turn itsef off. the code stored in "memory" will not
cause you to fail an inspection.
only active codes (SES light on) will, or excessive number
of "not ready" monitors.
in my area, and many others, a certain number specific
"not ready" flags are permitted, usually two.
but a cat monitor "not ready" is usually not allowable.

every time you clear the codes all readiness monitors are
reset to "not ready", and have to run again.
the cat monitor should complete after a few cycles
at light highway speeds.
the evap is more picky. on some vehicles, it might not
complete for years...
basically, the evap test tries to run after a cold start,
in park, at idle, air temps between 40-75 deg. F,
and fuel level not under 1/4, and not over 3/4 full.

if fuel level and air temp requirements are met, try letting
the truck idle for a couple of minutes after a cold start
to giv it a chance to run the monitor test.

if its failing the evap test, and thats whats setting your
SES, then there are several things that could be causing
a leak in the system.
anything from a loose or bad gas cap seal, loose hose clamps
on the filler pipe, damages tubing /piping, or a bad O-ring seal
between connections, an improperly tightened "test port" cap
(green colored) by the purge valve, faulty "test" valve, located
near the evap (charcoal) canister. even a damaged or punctured
canister, ect.
a faulty purge valve on the intake manifold,

find out whats causing the the code to set and fix
the problem

Last edited by Crew Cab Sonoma; 12-09-2009 at 10:39 AM.
Old 12-13-2009, 10:25 PM   #6
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Re: EVAP/Cat CODE Failing inspection... help!

ok truck failed inspection again.

Code is P0446..."Evap emission control system vent circuit malfunction"

What to do? (
Old 12-13-2009, 10:45 PM   #7
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Re: EVAP/Cat CODE Failing inspection... help!

imma take a guess and throw it out there, but could there be condensation in the air/smog pump below the radiator?

mine threw a code, don't remember which...but i took it off took it apart and it dripped a lil bit of water in there...so i let it dry and threw it back together, SES light gone. just an idea.
Old 12-14-2009, 11:18 AM   #8
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Re: EVAP/Cat CODE Failing inspection... help!

a list of things to start checking is listed at the bottom of post #5.
Old 12-14-2009, 11:21 AM   #9
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Re: EVAP/Cat CODE Failing inspection... help!

Quote: Originally Posted by 01x.joyride
imma take a guess and throw it out there, but could there be condensation in the air/smog pump below the radiator?

mine threw a code, don't remember which...but i took it off took it apart and it dripped a lil bit of water in there...so i let it dry and threw it back together, SES light gone. just an idea.
its an evap system code, not air injection related.
Old 12-14-2009, 12:23 PM   #10
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Re: EVAP/Cat CODE Failing inspection... help!

Quote: Originally Posted by Crew Cab Sonoma
its an evap system code, not air injection related.
gotcha!! i thought the smog pump bullshit might have been emissions related or something along those lines!! thanks for clarifying though!
Old 12-14-2009, 04:03 PM   #11
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Re: EVAP/Cat CODE Failing inspection... help!

Quote: Originally Posted by Crew Cab Sonoma
a list of things to start checking is listed at the bottom of post #5.
yes im going to start going through this somehow. tHe temperature thing will be quite difficult here because of winter
Old 01-17-2010, 10:36 AM   #12
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Unhappy Re: EVAP/Cat CODE Failing inspection... help!

I'll come on board and contribute to this topic since I too have been facing the dreaded p0446 code on my 4.3 liter 6 cylinder 6 cylinder '03 Xtreme (75k) I checked first the fuses. Then, the hoses, then proceeded to begin throwing parts at it. I changed out the precat passenger side 02 sensor (That was FUGLY B*tch to remove), then swapped out the charcoal gas canister. The code remains showing. Next, I'd like to check/change out the "Evap emission control system vent circuit". I think this is the little box that's right next to the charcoal canister that recieves the little plug connection wire and has a large air vent tube connecting it to the canister. Or is that little box a solenoid? Can someone help me with locating the "Evap emission control system vent circuit", and how to check it?:rolleyes: I'm almost ready to bring it in to the dealer and bend over.
Old 01-17-2010, 01:39 PM   #13
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Re: EVAP/Cat CODE Failing inspection... help!

Quote: Originally Posted by whiteblaze
Hello:

Ive got a 2001 2door 2wd 5speed Blazer with a little over 78,000 miles...its actually for sale but in order for me to sell it, it needs to pass inspection.

I need some help... the truck sat all summer (winter use only vehicle) and when it started a month or so ago the check Engine light came on. I used a scanner thing and got the light to go off.

Inspection time comes and it keeps failing inspection. Machines are telling me about a cat system not completed as well as evap system not completed.

The shops and the guys i know say i just have to drive it...

What do I need to do? replace vacuum lines? where are they and how difficult or expensive is this?

Any help is much appreciated.

Paul
Are you in Massachusetts by any chance? I am an inspector in MA, Not ready just means the monitors havent cleared yet.... you most likely wont get the EVAP to clear for inspection which is normal.. cat should clear.. im not possitive what the GM cycle is to clear the monitor, i know ford is 10 minutes at speeds between 25 and 45
Old 02-06-2010, 02:46 AM   #14
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Re: EVAP/Cat CODE Failing inspection... help!

Replace the Evap vent Valve, our trucks are notoirious for Failing Vent valves. Vent valves are open all the time so you can refuel the tank and the gas pump doesnt stop prematurally before full. The vent valve shuts to "purge" the gas vapors into the engine while driving at highway speeds. Trust me, I replaced mine at 76k miles just for the fueling issues. On customers s10 and blazers the vent valve failed becuase it wouldnt seal close or close when i commaned it to seal the evap system and smoke tested it.
Old 02-06-2010, 11:36 AM   #15
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Re: EVAP/Cat CODE Failing inspection... help!

Quote: Originally Posted by madscientist101
Replace the Evap vent Valve, our trucks are notoirious for Failing Vent valves.....
Where is the evap vent valve? Isn't that actually attached to the gas charcoal canister, the little tube that attaches to one of the purge hoses? Please excuse my ignorance. In addition, I'm want to try the voltage test to see if the connector wires to the precat 02 sensor are getting juice. There are 4 wires, which ones are supposed to have juice? Anyone have any special advice for a novice?
Old 02-06-2010, 01:32 PM   #16
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Re: EVAP/Cat CODE Failing inspection... help!

If you are getting a vent circuit code and you have changed the vent valve before and still get the code. you need to test the circuit. Which involves using the GM Tech2 and a test light. Tell the Tech2 to seal the evap system and check if you have pwr and grd at the harness side of the vent valve. If you dont test then you might have a wiring harness issue or the computer is mest up. If thats the case, then you need to tune out the Code for the Vent valve.
Old 02-06-2010, 02:33 PM   #17
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Re: EVAP/Cat CODE Failing inspection... help!

[QUOTE=madscientist101;6780281]If you are getting a vent circuit code and you have changed the vent valve before and still get the code. you need to test the circuit. Which involves using the GM Tech2 and a test light. Tell the Tech2 to seal the evap system and check if you have pwr and grd at the harness side of the vent valve........QUOTE]


This all sounds a bit over my head at this point. I have a test light, but where do I get the GM Tech2, how much $$ is it?? I have not changed the vent valve. Repeat: where is it? How do I test the circuit and use GM Tech2 tool? Thanks....I'm beginning to feel like a mad scientist now too
Old 02-06-2010, 02:53 PM   #18
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Re: EVAP/Cat CODE Failing inspection... help!

THe Tech2 is a diagnosing scanner that all GM dealers use. My boss bought one along time ago when he worked for Surf Chevy before they closed down. He bought because he was tried of waiting to use the only one that the shop had. The scanner is very expensive. the scanner is about 4grand but the Snapon Solace is about 6 grand and more acessable than the Tech2.

From 5 years of hardcore diagnosing i suggest changing the Vent Valve that is connected to the Charcol canister. they go bad on S10s but you can only get them from ACdelco or the Dealer and they are alittle pricy.

How ever you can bench test the valve. remove it from the charcol canister. Then take a set of wires and supply pwr and grnd to the valve it self at the battery. if you hear it click then blow in the canister's side of the valve and see if it holds pressure. The coil in side the vent valve must of shorted. Remember the Vent valve is always open for refueling. When you supply pwr and grd it should close.

Last edited by madscientist101; 02-06-2010 at 02:58 PM.
Old 02-07-2010, 11:34 AM   #19
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Re: EVAP/Cat CODE Failing inspection... help!

Quote: Originally Posted by madscientist101
THe Tech2 is a diagnosing scanner that all GM dealers use. My boss bought one along time ago when he worked for Surf Chevy before they closed down. He bought because he was tried of waiting to use the only one that the shop had. The scanner is very expensive. the scanner is about 4grand but the Snapon Solace is about 6 grand and more acessable than the Tech2.

From 5 years of hardcore diagnosing i suggest changing the Vent Valve that is connected to the Charcol canister. they go bad on S10s but you can only get them from ACdelco or the Dealer and they are alittle pricy.

How ever you can bench test the valve. remove it from the charcol canister. Then take a set of wires and supply pwr and grnd to the valve it self at the battery. if you hear it click then blow in the canister's side of the valve and see if it holds pressure. The coil in side the vent valve must of shorted. Remember the Vent valve is always open for refueling. When you supply pwr and grd it should close.
Thank you, Mad Scientist! This is good trouble-shooting info. Now I just replaced the old/original charcoal canister (75k) with a "new" one I got off Ebay for $25. New one has only 43k miles on it. I'm assuming the vent valve on the "new" would still be good/functional. I'll do the bench test you mentioned, but I can't do it any time soon since my weekends are pretty much full for the next couple months. I can see this becoming a 3 hour project. One more question: Do you have a lead on where to get that vent valve replacement and the part #? A Website, pictures would be nice.
John
Old 02-07-2010, 12:55 PM   #20
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Re: EVAP/Cat CODE Failing inspection... help!

I get My ACDelco parts from the dealer but i also get it from my boss' parts supplier named National Parts Supplier aka Cals. I pay only cost for parts. I recomend using ACDelco since its factory parts. I do believe Advance auto parts have expanded there supply of ACDelco. they might be able to get it for you. I might be alittle on the expensive side but not as expensive as the dealer. I personally would spend the money and not go cheap from stuff from china
Old 02-07-2010, 09:57 PM   #21
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Re: EVAP/Cat CODE Failing inspection... help!

Thanks. Now I'm reading up and see that I should also check the purge valve solenoid that is under hood, passenger side too. What do i look for there?
Old 02-08-2010, 09:26 PM   #22
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Re: EVAP/Cat CODE Failing inspection... help!

well the purge solenoid runs on controlled voltage much like the iac. How ever the purge valve would stay closed with no voltage. when you supply voltage it opens. The computer would give a limited amount of voltage to open it halfway, 1 quarter way, 3 quarter. or full open depending on the conditions:mph, rpm, load, temp, etc. remember no volts closed, pwred up open. If the solinoid failed mechanicly or electronicly, you would get drivability issues, lean codes. circuit codes for the purge.
Old 02-09-2010, 02:44 AM   #23
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Re: EVAP/Cat CODE Failing inspection... help!

Here is the GM ODB II cycle.
General Motors Driving Cycle

A complete driving cycle should perform diagnostics on all systems. A complete driving cycle can be done in under fifteen minutes.

To perform an OBDII Driving cycle do the following:
  • <LI type=disc>Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
  • Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.
  • Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.
  • Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
  • Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
  • Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.
  • Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.
  • Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.
Old 02-09-2010, 03:06 AM   #24
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Re: EVAP/Cat CODE Failing inspection... help!

+1 on the canister vent solenoids being problematic. Its a pretty simple circuit. Two wires, one will be HOT(b+) in the run and start positions of the ignition switch. The other wire is grounded by the pcm when needed to operate the valve. Using a test light make sure there is power on one of the wires with the key on. If so bench test the valve like described above if you dont have access to a decent OBD2 scanner. The valve only has a two positions on or off. You should be able to blow through it easily if the valve is open.
Old 02-09-2010, 10:19 PM   #25
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Re: EVAP/Cat CODE Failing inspection... help!

Bench test is the only sure thing to test the valve. I only use the Tech2 and a Evap smke Machine to find leaks if i get a Evap leak and not a circuit code in the evap system
Old 02-09-2010, 10:34 PM   #26
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Re: EVAP/Cat CODE Failing inspection... help!

yeah replace the vent valve. its located on the big hose that comes off ur charcoal canister. i got mine from the dealer. and that was the same code i had and fixed it
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