vent valve troubleshooting

#1
I had to repair/splice the wires that power the vent valve after a tank drop gone wrong. So after I initially re-installed everything, I got the check gas cap (so i replaced it) then have had the P0455--large evap leak code ever since. I've paid it no mind until recently reading about how common the vent valve failure is and how simple it is to replace. For $18, I figured I could replace it with a new one, but now that I think back to my tank dropping misadventure, I'm wondering...

I'm not sure if the vent valve is getting power or if it's not working (or both). I disconnected the plug from the vent valve and stuck the lead into it and got a reading, but not sure what it should be?

I also checked the old vent valve for continuity (trying to rule out power supply as an issue). But I'm not sure it should/would give me a result if it was working or not working.

I guess i can just install the new vent valve, clear the code, and see what happens next. Worst case, i guess, is to drop the tank again and re-repair the power supply to the vent valve, but i'd like to avoid that at all costs. Then again, it could be something entirely different throwing this code, right? I'd say doubtful, but...

Any advice/suggestions/pointers/tips are much appreciated.
 

The_Roadie

Founding Member
Administrator
#2
Welcome!

We have schematics here you can download from a link in member Mooseman's signature. Great resource. Then you will know what voltage is supposed to be on which wires at the valve's connector.

When you repaired the wiring harness, did you use solder and heat shrink for a secure and water-tight connection? Butt (crimp) splices are the worst for reliability. Wire nuts are OK, but not waterproof unless you get the special sort of nuts.

How confident are you that the repair job is perfect, in other words?
 
#3
Well....short answer is I have very little confidence in the repair job. Now, as I think back, I used butt ends, crimped, and coated with a waterproof tape substance (rubbery painted on goo) that was the best solution I could find at the time. I was just happy it started and ran after the "oh s@#%" moment with the tank, which is why I'm revisiting it.

Anyways, I replaced the vent valve tonight. I guess I'm going to have to wait and see what happens. In the meantime, I'll check out moosemans resource and prep for Rd 2 of tank project with the proper wiring repair this time. Any recommendations on a specific wire/gauge?
 
#5
This came from a rainier wiring diagram. My multimeter reading was 5v when I tested the plug at the vent valve (after the makeshift splice job). Perhaps I so have an adequate power supply?
 

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AtlWrk

Well-Known Member
#6
I just went through a troubleshooting issue with my vent solenoid the other day and here's some advice:

At the vent solenoid connector the pink wire should have 12V with the ignition on.

With everything connected go to the engine bay. Behind and just below the PCM is connector C100 with 10 wires. The white wire (forward most slot on the side closer to the engine/vehicle center) is the vent solenoid control. Manually grounding this wire (with the ignition ON, engine OFF) should activate the solenoid. You can disconnect the connector and carefully ground the terminal with a piece of wire. You should get a definite and noticeable "clack" from the rear when the solenoid kicks on or off. Alternatively, you can leave everything connected and use a small pin to poke through the insulation of the wire and ground the pin (alligator clips help a lot here) to activate the solenoid.

A caution though: If you use the pin trick only stick the tip of the pin in enough to make contact. Don't push it through. And/or coat it with something when you pull it back out. That was ultimately my issue: during a previous troubleshooting adventure I had pushed a pin through thinking the insulation thinking it would close itself. NOPE. A few months later the hole in the insulation let the copper wire corrode badly, get brittle and break completely. :hissyfit: Return of the P0449. :hissyfit:

On that note: P0455 could be caused by a mechanical failure of the vent valve (e.g. gunk jamming it). If there was something wrong with the vent valve electrical circuit the PCM can detect it directly and would issue a P0449 code instead of the P0455. In other words, if P0455 is your only code then it is likely not a wiring issue.
 

budwich

Well-Known Member
#7
I think (based on readings) that the "monitor" of the circuit isn't as "active" (ie. continuous / encompassing) as could be expected and therefore the p0455 code which is more related to "unexpected pressure readings" still leaves room for electrical issues as a likely candidate. Further the "5v reading" is suspicious at best.
 
#8
Thanks AtlWork. A mechanical failure is highly likely as well at 10 yrs 110k+. When does the truck run it's emissions/evap test? I thought I had read somewhere that it only does it when the tank is full? I cleared the code and am currently waiting to see if it comes back or not.
 

AtlWrk

Well-Known Member
#9
Regarding the P0449:

CONDITIONS FOR RUNNING THE DTC
  • The ignition is ON.
  • The system voltage is between 6-18 volts.
  • DTC P0449 runs continuously when the above conditions are met.
That being said, this is based on a 2006 vehicle and 2005 may or may not even have a P0449 DTC.
 

bobdec

Well-Known Member
#10
AltWrk, correct there is no P0449 (solenoid circuit verification) for a '05 . For ref https://service.gm.com/gmspo/mode6/ . Select 'engine' next to your year in right box, then under trucks select 4.2 LL8 (for '06 and under, I use grp14 for my '07) and scroll to the DTC number. '06 has a 449 but not the '05.

acgator42, in that url look at 'secondary parameters' column for the P0455 tank has to be between 15% and 85% and throttle between 7% and 35% for test to run.
 
#11
Thanks bobdec, I'm almost down to 15%, and if i have to take the tank out again, i'll do it this weekend. I'd like to keep it as little fuel in it as possible.
 

AtlWrk

Well-Known Member
#12
I was able to splice in a new connector without dropping the tank. With the driver's side rear tire removed you can get to where the vent connector wires meet up to the main harness. I cut here and spliced in new wires with a new connector/terminals. Soldered and shrink wrapped. Takes a bit of blind fishing to get the connector out and back over the tank but still much easier than dropping it. This was when I thought the connector itself or the extension harness was my problem. Having dropped the tank once you should have a good idea how things are routed anyway.
 
#13
I hesitate to report prematurely, but so far so good after a couple days on the road. Filled up to about 1/2 tank yesterday...no codes.......

I spoke too soon. Looks as if im going to try and re-wire the thing.
 
#14
Ok, tank drop went much more smoothly this time around. I didn't have to remove it because i could reach the vent valve wires once it was dropped down about 6" or so. Was interesting trying to connect and heat shrink those wires back up in there. Anyways, re-installed everything and it fired back up.

Just stopped at AAP at lunch to clear the codes (disconnected negative terminal the first go around), and the scan gave me P0128 and C0035....curious...no P0455 (evap leak). So, i cleared everything and will wait and see what pops back up.
 
#15
Since I'm already this far down the rabbit hole without resolving my initial problem, I decided to try and replace the solenoid purge valve and while I was in there go ahead and replace my thermostat. The purge valve replacement went very well, better than I expected. I used the through the driver wheel well method. The thermostat, well, that was a beast. I had hopes of replacing the temperature sender also, but did not have a tool to get at it, so I did not replace it. Other than a face full of coolant, all went well. I'm running out of emissions parts to throw at this p0455 CEL. The filler neck is next....TBD
 

KNBlazer

Well-Known Member
#16
Sorrrrrrrrry for bringing this back from the beyond.... what was the fix? I am facing this P0455, already replaced the common parts... solenoid, vent valve, gas cap... next is a smoke test.... Need ideas in the event smoke test does nothing....
 

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