i have a 2005 silverado Z71, was on my way to work one morning and my display told me to tighten gas cap. i checked it and was not loose. i did replace it anyhow, bought a code reader, cleared the code and the light went out. 2 trips later, it was back on...p0449. does anyone have any DIY advice on determining if it's the EVAP vent valve, the EVAP cannister or the pressure sensor in the tank? I've checked hoses and connections and don't see anything obvious? I've been a diesel mechanic all my life and don't like to guess when troubleshooting, that can get expensive! should I just take to dealer for smoke test?

 

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Breanne
Chevrolet Customer Service

 

Evap cannister solenoid valve incorrect voltage at driver. I have a half azzed Haynes manual, and I would say whatever is driving the solenoid is the problem. I can look it up later and post.

 

Look under the hood for a fuse box. There is a 10 amp fuse from eng1, check there for a blown fuse. Also if fuse is good, test light or VOM check with key on for voltage.

 

that would be the fuel tank pressure sensor right? if the pressure inside the tank is equal to atmospheric pressure, it only sends 1.5 volts instead of 4.5? so if I checked output voltage on signal wire and it reads 1.5, that would be my fault? that happened on my father in laws truck, I just like to be sure before I start spending money!

 

Sorry, thats the evap cannister vent valve solenoid.

 

oops! you see, back when I started my career, there were no "computer controlled anything" - I kinda miss those days! so the vent valve solenoid controls voltage to the "driver" and the fuel tank pressure sensor basically monitors the system for leaks? they should make these obd codes just tell you what to replace! ha-ha. so on the back of my fuel tank is a small "roundish" valve - 1 elec connector & 1 hose - that"s the vent valve solenoid? then next to my tank (inboard of tank - laying horizontal is the evap cannister?) so if there's low voltage at driver, do you think the vent valve solenoid is to blame? BTW, I do appreciate you taking time to help me try to figure this out!

 

Ok, the code is the driver to the soleniod is low output. Thats why I suggested checking under the hood for voltage from fuse eng1.

 

hey Kevinkpk - well I checked the underhood fuse block. there is no fuse actually marked as eng1 like the Haynes book says it does, but I did a continuity check on every fuse in the whole truck, engine compartment & instrament panel - all were good. took voltage readings on all that were marked ign, pcm, etc...all were 12.3 or higher. so I unhooked the connector at the vent valve, it had 12+ volts, and checked it at the purge valve, and it was 12+ volts.? so, I'm leaning towards a leak in the system somewhere? i did notice on the evap cannister - it has quick disconnects on the lines...on the one coming from the vent valve (on the cannister itself) it's kinda loose - it'll move back & forth about 1/4" or so? don't think it's supposed to do that? anyway, hope it does ok - going to charlotte this weekend to watch the fastest accelerating anything on the planet...the top fuel dragsters, and fuel funny cars. when you can take a 500 cubic inch motor and make 8000 hp, it's a beautiful thing! 0-100 mph in .8 sec, it'll make your inners SHAKE! i'll probably drop the fuel tank to look at pressure sensor & haven't taken evap cannister down to look at it yet...guess there's still time. do you have any recommendations for a scan tool with bidirectional capibility, that won't require a second mortgage to pay for? take care.

 

I have an actron, it will read and clear for a 60-70$ at autozone. Best of luck!