Tracing wiring for EVAP p0449

[Scharper]

2003 Chevy Tahoe 5.3 4x4

I've traced this code down to the wiring that goes to the evap vent valve solenoid. Bench tested, the solenoid works fine. The problem is the wire that goes to it should be hot and it shows no voltage. From my research this wire comes from the 4WS fuse, which is hot. So somewhere in between the fuse box and the solenoid the wire is faulty. The problem is it seems impossible to trace the wiring by hand. I've been trying to find a wiring diagram that shows the path of this wire but it doesn't seem to exist. Does anyone know of such a wiring diagram or at least where this wire might have failed?

 

[Jimmy John]

The one on my saturn went bad about 3 inches from where it connected to the solinoid. It had a soft spot in the wire you could feel by hand. Good luck.

Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[retiredsparky]

Is it possible that the tank pressure sensor is malfunctioning? It is my understanding (which may be wrong) that the vent valve is controlled by that sensor.

 

[Scharper]

Is it possible that the tank pressure sensor is malfunctioning? It is my understanding (which may be wrong) that the vent valve is controlled by that sensor.

My understanding is that the evap vent valve is a ground side switch, as in, power is always applied to it and it is activated by the PCM applying ground to. Perhaps the pressure sensor shares the same positive wire and that has failed? Thats why I really want to see a schematic to see what all is in between the 4WS fuse and the vent valve. I have no idea where to find such a schematic though. Would haynes or similar have it?

 

[Jimmy John]

Go to autozone.com repair area they have schematics for your vehicle. You will have to start an account to see it I think?

 

[Scharper]

Go to autozone.com repair area they have schematics for your vehicle. You will have to start an account to see it I think?

I looked all over the repair help section the other day and couldn't find schematics anywhere. It looks like they have them for a few random things but not everything.

 

[Jimmy John]

Make sure you are logged in with your vehicle selected and Go here http://www.autozone.com/repairinfo/repairguide/repairGuideMain.jsp then select

• Wiring Diagrams at bottom of list.

then goto

• Engine Control Systems 2003

then look for

Fuel Controls - EVAP Controls, Fuel Tank Pressure, and Fuel Composition(c) (2003)

 

[Scharper]

Make sure you are logged in with your vehicle selected and Go here http://www.autozone.com/repairinfo/repairguide/repairGuideMain.jsp then select

• Wiring Diagrams at bottom of list.

then goto

• Engine Control Systems 2003

then look for

Fuel Controls - EVAP Controls, Fuel Tank Pressure, and Fuel Composition(c) (2003)

Thanks a ton! This section of their website isn't laid out the most logically.

I was hoping to see a relay or solenoid or something else inline from the 4WS fuse before reaching the vent valve but it appears not.. Onerous tracing by hand it is then..

Say is there such a thing as a non-contact voltage detector that I can just touch the casing of a wire and it will say if voltage is running through it? I know they exists for household AC current but haven't found one yet for 12v dc.

 

[Jimmy John]

Never heard of one. Did you try feeling for soft spots in the wiring near the connector?

 

[Scharper]

Never heard of one. Did you try feeling for soft spots in the wiring near the connector?

Not yet I'll try to get under it after work and look some more. That's why I was hoping for a non-contact tester, to check further up the wire. Maybe a test light and moving the wire around will reveal a short though.