2018 gmc sierra denali - P0449 code.

Hello.

I am hobby mechanic taking care of my own equipment only (2003 corvette z06, 2012 Yukon xl slt 5.3, 2018 sierra Denali 6.2)
Right now I have a code P0449 in the sierra and as you can see in the attached photos when the circuit is closed I get 12v and when it supposed to be open I get 9v that still operates the solenoid.
started as a "part changer" and replaced the solenoid and the purge valve then went and bought a bi directional scan tool (xtool d7)
Hope you can help, I love your approach.

Thank you.

Just checked each port to ground:
red wire reads 12v constant (venting and not venting)
white reads 3v when venting and 0v when not venting

Hey bikeril! Is this a hard fault code? If you clear it and cycle the key, does it come back immediately?

From your picture, it looks like a wiring repair has been done on this circuit previously. It also looks like you're testing ahead of the repairs. Is the vent solenoid connector itself difficult to access?

If possible, I'd suggest doing your testing at the solenoid connector itself. Use an incandescent test light connected to B- and check the red/green wire, pin 2. Should light brightly. Now turn the key on and use your scan tool to command the vent closed. Test light to B+, check the white wire, pin 1. Should light brightly any time the vent is commanded closed.

Hey Tyler.
thanks for responding.
the car never had that issue I`m 1st owner so if they ever fixed it, it was in the factory. the error code comes right when I turn on the switch.
I did the testing on the solenoid connector as well and it shows the same its just that I took the pictures while I tested above the diodes or whatever they are.
I also checked the solenoid with external battery and it clicks. is there any relay that switches that solenoid?

bikeril wrote:

Hey Tyler.
thanks for responding.
the car never had that issue I`m 1st owner so if they ever fixed it, it was in the factory. the error code comes right when I turn on the switch.

Interesting. :huh: Good to know.

I did the testing on the solenoid connector as well and it shows the same its just that I took the pictures while I tested above the diodes or whatever they are.

Also good to know. Those look like heat shrink butt connectors to me. But I could be wrong.

I also checked the solenoid with external battery and it clicks. is there any relay that switches that solenoid?

Where did you get the solenoid from?

There is no external relay that switches the solenoid. Just a hot-at-all-times fuse and the PCM switched ground. The incandescent test light will check the current carrying ability of both.

when I use The incandescent test light I get a strong light when not venting and a weak light when venting (12v vs 9v).
I bought the solenoid from amazon. www.amazon.ca/gp/product/B06Y5MFF9D/ref=...06_s01?ie=UTF8&psc=1

bikeril wrote:

Just checked each port to ground:
red wire reads 12v constant (venting and not venting)
white reads 3v when venting and 0v when not venting

This is a ground side switch circuit. You have resistance on the ground wire. I would take a closer look at that butt connector for bad contact or corrosion. As Tyler says it looks like a repair. Factory or otherwise those should be solid wires.

I guess my next test is white wires connectivity to ground, switched and not switched.
I`ll update
Thanks for helping out

Ok.. fixed!
when you said its a ground switch, it hit me,, so I went and checked white connectivity to ground and I found that this "resistor/diode/what not" is actually just a copper connector, they probably had to change the connector in the factory and did a bad job. anyway since I did not know what it is i bypassed it and everything was working. as you can see in the pictures the connector was corroded.

Thanks for helping everyone.!

Great to hear, bikeril!

@Monde,

I am wondering why we have 3v on the control wire when the solenoid is not commended on. The resistance should not matter if no current is flowing through the circuit, right?

I was wondering that too, I see diodes on the OE diagram, could be a ground side bias voltage if he measured upstream of that inferior connector.

Monde wrote:

I am wondering why we have 3v on the control wire when the solenoid is not commended on. The resistance should not matter if no current is flowing through the circuit, right?

I'm betting that's a control side bias voltage from the PCM. That's why it shows up with the solenoid disconnected but goes away with it plugged in. The excessive resistance in the butt connector isn't high enough to impact the bias voltage, but does reduce the current flow of the vent solenoid when energized.

Paul P. wrote:

I was wondering that too, I see diodes on the OE diagram, could be a ground side bias voltage if he measured upstream of that inferior connector.

WEYCRAZE! :woohoo: How ya been?

Hi Tyler,

I've been good!! Thanks for asking! This industry leaves no shortage of things to learn.

It's nice to see this site is being well kept and maintained, and some great talent by too many to list. Dynamite job.

Mr. Danner has 4 Gold bricks for Mods here!

Take Care!