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Discussion Starter · #1 ·
So my mother in laws truck has had a CEL for about 4 years and I've never bothered to check it cause it ran fine until recently lol. It's a 2006 Trailblazer LT i6 4.2L with about 270K miles.

Started off with a MAF, MAP, Coil 6, Low Idle Speed and some others I can't remember along side P0446.

I fixed all the obvious ones and only cleaned the MAF and Throttle Body now I have a reoccurring P0446 and now a P0171 which is new. It's been about a week since that and these just popped today.

P0446 - I've replaced the gas cap, and the purge solenoid. Replaced the old yellow clips that Crack on the lines etc.

Code is still present. I noticed the vapor canister has cracked line clips also, and she drives a very dusty dirt road in Florida so I'm suspecting it being clogged or flat out damaged. Solenoid hose was completely off due to broken clip. Didn't know of other things to check beforehand.

P0171- Too lean, I've only cleaned the MAF twice now. Truck doesn't really miss until you're doing about a 30 roll and mat it to the floor, it'll spit a bit and then clear up. Parts store immediately tried to sell me an 02 sensor which I didn't go for.

Other general symptoms it has, rough idle. Idle about 600-800 and sputters a little (not noticeable to someone inexperienced to it). Takes 2 attempts for the engine to start (I've read is a side affect of the evap leak), and will be extra hard to start after fueling or if she pumps past the first click a little.

I plan on replacing the MAF since I'm suspecting that's the cause of the P0171, but does anyone have any advice on what I should check alongside before buying more parts?

Thanks in advance.
 

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P0446 - I've replaced the gas cap, and the purge solenoid. Replaced the old yellow clips that Crack on the lines etc
As far as I know that code is not caused by anything leaking like a gas cap or loose hose.

It is too much vacuum in the gas tank due to some blockage of the vent system, like a clogged vent hose or charcoal canister.

57158
 

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I would pull off the evap vent solenoid and filter and either clean all the crud out of it or replace it. If that doesn't do it then you may have to replace the canister. Here is what I dumped out of my vent solenoid/filter some years ago...

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Discussion Starter · #4 ·
I would pull off the evap vent solenoid and filter and either clean all the crud out of it or replace it. If that doesn't do it then you may have to replace the canister. Here is what I dumped out of my vent solenoid/filter some years ago...

View attachment 57159
Yeah, I put a new solenoid. I'll probably need to buy a canister since all these parts are still oe on it with 270k miles lol. I just didn't know if there was a secondary valve that can be checked because I seen SS posts about one near the engine bay but I personally cannot find it myself on the LT trim.
 

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That valve (don't remember the name of it) is on the drivers side of the engine, down low, in about the middle of the engine. It can be reached without taking anything else apart.
 

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Ok, so maybe some confusion here. There are two solenoid valves. The purge valve/solenoid is low on the drivers side of the engine. That valve opens the vapor system to engine vacuum as desired by the PCM.

The vent valve/solenoid is located back by the fuel tank. That valve is normally open from the atmosphere to the vapor system. It only closes when the PCM needs to test the system for leaks.

The original post said nothing of the vent valve, just the purge valve.

As for some code(s) being "new",,, many tests for codes do not run if there are certain other codes already set. No point in testing some systems if certain related systems are already reporting trouble. Thus when you fix and clear some codes shortly later other "new" codes pop up. The defect is not new, just the test test now runs and tells you about it
 

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Discussion Starter · #7 ·
Ok, so maybe some confusion here. There are two solenoid valves. The purge valve/solenoid is low on the drivers side of the engine. That valve opens the vapor system to engine vacuum as desired by the PCM.

The vent valve/solenoid is located back by the fuel tank. That valve is normally open from the atmosphere to the vapor system. It only closes when the PCM needs to test the system for leaks.

The original post said nothing of the vent valve, just the purge valve.

As for some code(s) being "new",,, many tests for codes do not run if there are certain other codes already set. No point in testing some systems if certain related systems are already reporting trouble. Thus when you fix and clear some codes shortly later other "new" codes pop up. The defect is not new, just the test test now runs and tells you about it
Oh. My mistake, I thought they were tied to the same CEL code. I've googled the p0446 like 100 times before making this thread so I was confused about it. Because people would say to replace that, or replace the solenoid up above the rear diff. If that one has its own CEL, then I'll just jump straight for the canister.
 

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Discussion Starter · #9 ·
So have you replaced or cleaned out the vent solenoid over the rear differential?? THAT is the one this P0446 code is about. Either that or the canister.
Yeah I replaced the solenoid above the rear diff, I'm going to try to replace the canister above the rear diff as well now.
 

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Discussion Starter · #11 ·
Those "quick" connectors truely suck and are not quick at all for the mechanic. Only quick for the assembly line I think.
Yeah they really do. The little locking clips break when attempting to undo them or they're already broke from age lol. I bought 2 boxes of them from AutoZone cause I knew I'd snap a bunch lmao
 

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Discussion Starter · #12 ·
H
Those "quick" connectors truely suck and are not quick at all for the mechanic. Only quick for the assembly line I think.
Hey do you happen to know of a cheaper source for the vapor canister? I've checked like O'Reilly AutoZone etc & even RockAuto but they're still all above $130 for ACDelco part.

Not sure if you knew of one cheaper somewhere.
 

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rockauto.com is likely the least expensive. For a non EXT TrailBlazer/Envoy, an ACDelco canister is about $109.
 

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As far as the lean condition goes, have you checked the condition of the intake gasket or made sure that all bolts are tight? Also check for vacuum leaks.
 
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