Evap vent solenoid

jeepdad · June 20, 2019

06 Sierra 0449 code. I replaced evap vent solenoid. still throwing code. I just checked voltage to solenoid and with key off I'm getting battery voltage at the plug to solenoid. Is this normal ? any ideas would be greatly appreciated.

sefiroxx · June 20, 2019

Don't have a fsm in front of me but . .
The circuit may be controlled on the ground site vs the power side and if so, yes, there would be voltage.

If, it is controlled through a relay and the relay is stuck on.

Hook up a spare hose and see if you can pull air through it

RStrain56 · June 20, 2019

I had the same code and replaced my solenoid as well. Stupid questions probably, but did you manually clear the code and it came back, or it has yet to clear? Mine took about 30 miles or so to self clear.

I realize you've likely done that, but just trying to help where I can!

Sent from my SM-G965U1 using Tapatalk

tbarn · June 20, 2019

Voltage with key on only.

carnau · June 20, 2019

1 hour ago, tbarn said:

Voltage with key on only.

This is incorrect. You have B+ Voltage all the time to the Orange wire. It is a commanded ground from the ECM on the white wire.

tbarn · June 21, 2019

4 hours ago, carnau said:

This is incorrect. You have B+ Voltage all the time to the Orange wire. It is a commanded ground from the ECM on the white wire.

You are absolutely correct. Should have looked it up before shooting from the hip. I know better.

jeepdad · June 21, 2019

I have used my code reader to clear the code. at least I know now thanks to you guys that it's good that I have voltage at plug so I don't have a broken wire somewhere. although I'm still scratching my head why I'm throwing the code. I assume I could have a bad solenoid, although it was replaced before I bought the truck (2 weeks ago) and I replaced that solenoid the other day and still has code.

jeepdad · June 21, 2019

The solenoid should vent at key start up I believe, so if I check voltage at key startup or engine startup one or the other, I should see a change in the white wire? Is this correct, but if there's no change maybe I have a an open white wire.. or for some reason not getting command to solenoid for some reason. what say you guys?

riverbanks · June 21, 2019

It's not written on stone with these codes,go to www.700r4transmissionhq.com,Chevy Silverado po449 code diagnosis, some good info

jeepdad · June 21, 2019

much appreciated!

redvett · June 21, 2019

The evap test is random and will not go out if solenoid is replaced, you must clear with a scanner. If it comes back on later you most likely have a leak.

carnau · June 21, 2019

19 minutes ago, redvett said:

The evap test is random and will not go out if solenoid is replaced, you must clear with a scanner. If it comes back on later you most likely have a leak.

You won't have a circuit control code for a leak.

A P0449 is a control failure. Which means the computer isn't seeing the control pulled to power when commanded.

In this case you have 4 possible failures.

1.) The component. Which you changed.

2.) The B+ positive wire which you have tested and found to be good.

3.) The Negative control wire. Which you would need a Scanner that gives you special functions and can command the vent open and closed.

4.) The ECM. You would test this after finding out the command circuit has tested good but failing to send the command.

These are the only probable outcomes other than a power/ground issue to the ECM which would also be tested in the last step, but with this being the only problem, and multiple components using the same ground, i highly doubt this is the issue.

All in all, You need a better scanner to be able to diagnose this issue properly.

carnau · June 21, 2019

2 minutes ago, carnau said:

All in all, You need a better scanner to be able to diagnose this issue properly.

I'm quoting myself now...

Or you could run a whole new wire from the ECM to the Vent and then you would know that the command wire is good, the component is good which would mean the ECM was bad... which I highly doubt is the case.

This would take a lot of time, some special tools, and special terminals.

If it were me, I would find someone with a better scanner.

mjm-1957 · June 21, 2019

Or you could easily take a test light and place it across the connector to the vent solenoid and command the vent solenoid on and off with a scan tool and see that the test light goes on and off with the command. If it does plug it back in and command the solenoid on and off with the scan tool ,it should click with each command. If it does the wiring to and from the ECM is good.

carnau · June 21, 2019

3 hours ago, mjm-1957 said:

Or you could easily take a test light and place it across the connector to the vent solenoid and command the vent solenoid on and off with a scan tool and see that the test light goes on and off with the command. If it does plug it back in and command the solenoid on and off with the scan tool ,it should click with each command. If it does the wiring to and from the ECM is good.

Test light will not work. It doesn't have enough resistance to let the ECM know that there is something in line. It will think that the system is shorted and give you the same code. You can do this with a Hi Beam head lamp bulb or a old sealed headlamp bulb.

But you're exactly right. You can do this with a scan tool which is why I said, you need a better scanner.