P0449 Help....AGAIN

GDM Z28 · August 19, 2014

Ok so I have searched and read until I was blue in the face and my fingers hurt. I have a 2008 GMC Sierra 1500 that threw a P0449 CEL. The truck was at a friends shop for inspection and he tested the gas cap and the gas cap passed (I also tried a new one he had there) so I am ruleing the gas cap out. I didnt want to take any chances so I replaced both solenoids (the one on the intake manifold and the one by the gas tank that comes with the charcol filter). I reset the CEL and as soon as I start the truck the light comes on right away. I am stumped. Anyone have any sudgestions on where I should start looking next? Thank you so much.

Duelin · August 19, 2014

P0449 2008 GMC SIERRA 1500 V8

EVAP Vent Solenoid Control Circuit Fault
The ECM detects the voltage on the EVAP canister vent valve control circuit is between 2.6-4.6 volts when the driver is commanded off for more than 4 seconds

Probable Cause

Open or short circuit condition
Poor electrical connection
EVAP canister vent valve
ECM fault

kstruckcountry · August 19, 2014

It could be the evap canister as well... I replaced the vent solenoid on mine, then found out that the canister was full of crap as well... I would check it out.

GDM Z28 · August 19, 2014

It could be the evap canister as well... I replaced the vent solenoid on mine, then found out that the canister was full of crap as well... I would check it out.

Would that be the plastic box that the solenoid by the gas tank connects to? If so what do I do? Open it up and clean it out? Any input would be appreciated.

GDM Z28 · August 19, 2014

Because I replaced the soilenoid on the intake manifold and I replaced the one by the tank. The one by the tank came with a new little filter box so I mounted that again and ran hose to connect the filter to the solenoid

kstruckcountry · August 19, 2014

Yep that's the point I'm at. I replaced the old solenoid with the updated style. Ran for 1000 miles and then the code was back. Then turned out that the vapor canister was full of junk. You should be able to unhook a hose and look inside to see if it's ok. Not sure if it can be cleaned out, I just ordered a new one.

However that may not be your problem, but it's worth checking I think. You have a different code than I do so there could be another issue. If you can take it to a shop with a GM scanner, they can hook it up and run a diagnostic to pinpoint the issue. Also can force solenoids on or off to check their operation and draw.

txab · August 20, 2014

Always an informative read:

http://www.gm-trucks.com/forums/topic/104569-the-evap-system/

GDM Z28 · August 20, 2014

Yep that's the point I'm at. I replaced the old solenoid with the updated style. Ran for 1000 miles and then the code was back. Then turned out that the vapor canister was full of junk. You should be able to unhook a hose and look inside to see if it's ok. Not sure if it can be cleaned out, I just ordered a new one.

However that may not be your problem, but it's worth checking I think. You have a different code than I do so there could be another issue. If you can take it to a shop with a GM scanner, they can hook it up and run a diagnostic to pinpoint the issue. Also can force solenoids on or off to check their operation and draw.

Well I'm pretty sure the p0449 code I have is electrical. I'll have to see if my friends solus can command the evap solenoid to turn on and off and I'll check power and go from there. I hope it's not the ecm it's self.

gmtech4 · August 20, 2014

you have to thru the printed diagnostic table step by step ,,,,,,,this is not difficult ,,,

when a step stops you then its off to a shop ,,,,simple

GDM Z28 · August 20, 2014

you have to thru the printed diagnostic table step by step ,,,,,,,this is not difficult ,,,

when a step stops you then its off to a shop ,,,,simple

What's simple to some is not always simple to others. Care to elaborate?

gmtech4 · August 20, 2014

ya dont throw parts at it ,,,ya can but thats dumb ,,,if you by all data and try to follow the steps at some point you may not be able to continue its time for a garage to finish ,,,you need auto training ,electrical experience etc etc

there is only 10 or so computers on todays vehs,,,,not much a DIYer can do now adays imo

GDM Z28 · August 20, 2014

Well I have power going to the solenoid. But when I close it or open it with the solus I do not get a ground

Duelin · August 20, 2014

How did you check for ground when you commanded it on?

GDM Z28 · August 21, 2014

How did you check for ground when you commanded it on?

I put a paper clip in the power side the commanded the valve then checked to see if I had ground on the other side. I had nothing. So I used a multi meter to check if I had a connection from pin 61 at the ecu to the plug and I didn't so I knew the wire was broken somewhere. I soldered a new wire at the plug and ran it to the ecu harness and soldered it on the other side. I commanded the valve and I heard a click. Fired it up and the light went out. All fixed.