[Wareever]

2005 Trailblazer 4.2L I6: Recently purchased this vehicle and had a new fuel pump installed since the fuel gauge was not working. Immediately afterwards, I was getting the P0455 code. Tried the new gas cap, then had them check their connections again, but still getting the code. Rather than start throwing parts on it, I took it elsewhere to have a smoke test done thinking they may have installed/reconnected something improperly. The new shop found that the vent valve was bad, so had it replaced. That lasted a day or two, but now still getting the P0455. Took it back today and they found that the vent valve is getting intermittent power to it and throws the code. They had checked it and found it had power, then all of the sudden it didn't. Any ideas what could be the cause of the intermittent power? They said they could not see anything out of the ordinary that may have happened when the first shop replaced the fuel pump. The vehicle does run well with no other issues.

 

[budwich]

most controls "items" have power to them at all times during "key on / run". IF you are getting "flaky" voltage (assuming they measured / monitor it correctly), then you need to check / clean connections along the powering path back to the fuse. Possible causes may be a loose fuse in holder or broken / pinched wire along route.

 

[Wareever]

Will be taking my test light and tracing it back. Was told it shares the same fuse as the purge valve solenoid, which had power when the vent valve didn't.

 

[budwich]

based on diagram, true. That potentially rules out the fuse but not necessarily a connection at the block. sorry but I don't know where the splice points are. I would "backtrack" just a bit back from the connector at the valve as the best guess would be a poor connector / wiring at the valve itself depending on how they checked it. Again, the voltage at the valve should be solid, the operation ground is "thrown on" when the system wants things to happen.

 

[Wareever]

I appreciate your feedback. Really needed some help in my thought process about this. This is my wife's car so I want to make sure I stay on top of it and get it solve. (Will worry about my intermittent airbag light on my 04 Blazer later.) I thought I would get a different code rather than the P0455 it's giving if it is actually an electrical issue. Was aware of these vehicles having fuse block issues so will look there also. Was worried about possibly being a bad PCM, but it throws the ground like you said to the valve which should have current all the time, which it doesn't. Will dig into it this weekend.

 

[budwich]

just to make sure you understand.... you state "current"... its not current, its a voltage, quite different. The current only flows when the ground is added (by the pcm) to complete the circuit and operate the valve.

As for the PCM nicely telling you that its an electrical issue, that's unlikely in general, and in this case in particular since the pcm has no way to figure that out. Typically, that is only possible on sensors where there are "reference voltage" levels involved.

 

[Wareever]

But when tracing the voltage starting at the connector when disconnected from the vent valve using a test light, the light should be on should it not (for tracing purposes)? The voltage should be supplied straight from the battery meaning a constant 12.4 +/-, correct? And should this be with the key in the off and in the on/run positions (constant)?

 

[budwich]

As I mentioned in the earlier post, the voltage is only there with key on. Of course, the question becomes, how are you connecting your test light? IF it is not connected properly then your results will likely not be of much value.

 

[Wareever]

Would you happen to know what the fuse number/name is for the canister vent valve on an '05 I6? I do have the owner's manual, but I don't see it listed for the I6 in the engine compartment or under the rear seat unless it is called something different. The V8 is listed as "canister vent", but nothing labeled as such for the I6 unless I'm missing it. (Google didn't help me...)

 

[budwich]

fuse 28 under the hood ... maybe. Not all "unofficial references" are good for fuse numbering... my findings in the past.

 

[Wareever]

Labeled "Powertrain Control Module 1"?

 

[budwich]

???? as you indicated in your "comeback", the fuse is used by a number of "things", so labelling may not be "precise". Further, diagrams shows that the fuse block has "multiple" connections leaving from that fuse. Perhaps the one going to the valve has an issue while others are ok. Just a statement of possibilities based on diagrams.

 

[Wareever]

Thanks, budwich. I had checked all the fuses last night, which were all good, reset number 28 for the heck of it and then cleared the code. I'm sure it'll come back, so I'll crawl underneath on Saturday and see if I can find something. I sincerely appreciate your input.

 

[Wareever]

So, I crawled underneath the vehicle and there dangling next to the new vent valve was the wiring to it. But before just reconnecting it, I checked it and sure enough there was no voltage to it. There is a connector about 6" up just at the edge of the tank so I disconnected it and had voltage there. Ends up that the one pin in the connector was not protruding enough to make good contact within the connection. Fixed that, reconnected it and now getting voltage to the vent valve. Cleared the code and will see what happens.

 

[acgator42]

I'm anxious to hear your results after a couple days and see if you pinpointed the problem. I've had the p0455 for awhile now and don't know where to start to begin to troubleshoot it. I have an '05 tb I6 as well.

 

[acgator42]

Ok, so I started to dig into this a bit more last night. I pulled out the multimeter to see if I have power at the vent valve. What voltage should it be reading back there, 12 +/-? What's the best way to disconnect the vent valve plug?

 

[Wareever]

Well, that did it. No more light. They must have pulled on the wiring a bit when they replaced the fuel pump. I used my test light, but I would think you should be getting 12v with the key on when you check it at the vent valve. I used the drive shaft u-joint bolt as my ground, which worked well. Other frame parts should work also. Just glad the bad connector that wasn't connected properly was reachable or I would have had to drop the tank.