p0449 on a 2007 GMC YUKON 5.3flex

Have replaced the EVAP vent solenoid already. I believe I have a bad control wire (WNY Rust Belt). I have 12 (and some change) volts from the ECM, but have 0 volts at the EVAP vent solenoid (from connector to about 12 inches into wiring harness). I have no way of turning the driver on or off (no scanner) to verify. Is the wiring the same color all the way from ECM to solenoid (believe it is pink/white)? Don't want to short anything out by running new wire to the incorrect wire haha.

Hey Woozybiffo420! Just to be clear, you've measured for power at the vent solenoid, and found it? Will that same power wire light a test light connected to ground?

I'll grab the wiring diagram when I get to a computer later today, but it sounds like you're describing a lack of power to the vent solenoid. Unfortunately, wiring problems are very common for these trucks, even when they don't live in the rust belt. :lol:

I have power on one side of the solenoid, it was my understanding that both sides should have power until the driver commands otherwise. Am I thinking incorrectly?

Nope, you're thinking correctly! With the key on, back probing, there should definitely be power on both solenoid wires.

My next suggestion would be to connect a test light to B+ and touch on the control wire. If it lights, the either the control wire is shorted to ground, or the driver in the PCM is shorted to ground.

If it does not light, then there's still some kind of open circuit at the vent solenoid, possibly due to pin fitment or corrosion. Let us know what happens with the test light, and we can go further as needed.

Here's the diagram:

Alright finally had a chance to get under the yukon this weekend. I found that the plug that connects the after market harness to the actual solenoid was not plugged in all the way!!! (Thinking that would fix it) cleared the light started it, no light. Shut it down and started it again, boom p0449. So now I have power on both sides and no way to cycle the driver. I did the test you told me too and test light did not light, before the connector was plugged all the way in and after and neither wire has ground just power.

Woozybiffo420 wrote: Alright finally had a chance to get under the yukon this weekend. I found that the plug that connects the after market harness to the actual solenoid was not plugged in all the way!!! (Thinking that would fix it) cleared the light started it, no light. Shut it down and started it again, boom p0449. So now I have power on both sides and no way to cycle the driver. I did the test you told me too and test light did not light, before the connector was plugged all the way in and after and neither wire has ground just power.

Thanks for the update! Well, we got power now, but clearly the PCM still isn't happy with that circuit. :huh:

Now that we've got a power feed, I think your next move is to recheck for voltage at the PCM itself. OR, there's another option:



It looks like C300 is a bulk connector that has the fuel tank pressure, the pump, the vent valve and the level sender in it. I don't know where C300 is, exactly, but it's the next easiest place to check if you can locate it.

If you can't find C300, or it's a pain to get to, just go direct to the PCM. Pin 61 of C1, a white wire with no wires to either side (according to the diagram, anyway). KOEO, there should be 12V. If you find 12V, then that would suggest a PCM problem. If you find less than 12V, that would suggest more wiring issues.

Let us know what you find, and we can figure out the next step.

So I have .40 volts at the ECM/pcm white wire. I have 12.1ish at the red/white wire at the evap vent solenoid and 0volts on the control / white wire. If I have .4 volts at the computer, would that tell me the computer is the culprit?

Thanks for getting back to us!

Woozybiffo420 wrote: So I have .40 volts at the ECM/pcm white wire. I have 12.1ish at the red/white wire at the evap vent solenoid and 0volts on the control / white wire. If I have .4 volts at the computer, would that tell me the computer is the culprit?

The 12V reading on the red/white wire is definitely good, but I thought you had 12V on the white wire at the solenoid? :huh: Not trying to nitpick, just making sure I understand where you're at.

So, with the key on and everything plugged in, is this accurate?



I ask because the above is describing either a functional circuit, or an open vent solenoid. If we actually have 12V at the vent control wire, and .4V at the ECM, then that is showing excessive resistance. Paul: "Make sense?" :silly:

So I am a bone head and was testing while the solenoid was not plugged back in. I have 12v in 12v out and .4 at the ECM.

Woozybiffo420 wrote: So I am a bone head and was testing while the solenoid was not plugged back in. I have 12v in 12v out and .4 at the ECM.

:lol: No worries! In that case, you're DEFINITELY looking at an open/high resistance in the control wire.

This is where finding where C300 comes in, as it'd enable you to split the circuit and reduce the amount of wiring you'd need to check. Otherwise, you're down to visual on the harness, or picking the control wire out of the harness and testing for voltage.

OR, if you just want the stupid thing fixed, run a new wire. :lol: It's not the ideal solution, but it is one I'd consider if my best efforts to find the issue got me nowhere.

So I ran the new wire, everything was fine. Mutiple start cycles NO light!! Truck sat for about an hour and a half, went out to try it again, the f'n Light is back on. Being it was wearing my patience i have not rechecked the wire for 12v. I wish a tree would fall on this thing

Yeah, it's good to take a break sometimes. :lol: When you get around to it, let me know if it's the same code? The light stayed out initially, so we KNOW we fixed something! :silly:

It is still the same code p0449.

*sigh* I was hoping it'd be a large leak code or something.

Oh well, we can still beat this! Let me know what voltage you find at the PCM when you have time?

Gonna grab a cheap VOLTMETER on my lunch and see what i come up with. When I ran that wire i was about foot short (of where i would have liked to be) and it had a smidge of tension on it. I am hoping the wire may have pulled on the plug a little bit.

Alright so, pretty sure it is the shitty plug on the new solenoid I bought. There isn't as much tension as I thought there was last night when i finished. I am going to work on it tonight when I get home. I am pretty sure it is just that connection that is losing signal back to the computer. I will report back what I come up with.

Possibly? You had 12V on the control wire at the solenoid earlier, so we know that connector was making some kind of contact, anyway.

Let me know what you find with the voltmeter. What happened to the one in your picture from before? :huh: