SES Light on

[nflskinfan]

SES light on intermittantly w/P0440. Checked for fuel leaks and found none. Recently changed fuel pump, but light was on before that. Changed fuel cap also, but no joy. Light will go off somedays after a few miles and other times it stays on for weeks. After the light is off for a couple of days and then comes on, I can smell fuel when I shut truck off, but can't tell where it is coming from. No noticable leaks around tank or pump or in engine compartment. Any help is appreciated.

[Cam7]

Check all the lines and hoses. also check the evap canister for leaks or might be bad, might need replaced.

[nflskinfan]

Originally Posted by Cam7

Check all the lines and hoses. also check the evap canister for leaks or might be bad, might need replaced.

I checked the hoses for what I could see and they look fine. I did have to replace the locks on the hoses that connect to the fuel pump. I will try the evap canister and pass any information on the this thread. I guess that it is lucky for me that I have another Chevy that I can swap parts with until I get this thing licked. Thanks for the help.

[nflskinfan]

I replaced the EVAP cannister and drove 100+ miles with the light never going out. When I got home, I replaced the valve that attaches to the can. I will update the thread after I drive it today.

[nflskinfan]

Replaced the valve that attaches to the EVAP cannister with 100+ miles again and still the light is on with no change. Any other thoughts? Thanks in advance.

Originally Posted by nflskinfan

I replaced the EVAP cannister and drove 100+ miles with the light never going out. When I got home, I replaced the valve that attaches to the can. I will update the thread after I drive it today.

[sharo23]

p0440 is slow leak detected in the evap sys.the pcm closes the sys up applies a vaccum in the tank, if the sys does not hold the vaccum it sets that code,slow leaks are tuff and best way to check it is to applay smoke to the sys using a smoke machine, seal the sys with a scan tool and look to see where the smoke is comming from.

[nflskinfan]

Originally Posted by sharo23

p0440 is slow leak detected in the evap sys.the pcm closes the sys up applies a vaccum in the tank, if the sys does not hold the vaccum it sets that code,slow leaks are tuff and best way to check it is to applay smoke to the sys using a smoke machine, seal the sys with a scan tool and look to see where the smoke is comming from.

Before I take it to a shop and have them use a smoke machine, it there something else that I can do? I read in my haynes manual today that there is a vent valve near the tank. Could that possibly be what is causing this? I'm trying to avoid the dealer since they do a lot of price gouging in my area and there isn't any smaller garages that I have been too that have earned my trust yet for things that I cannot do myself.

Thanks again for the help.

[nflskinfan]

Well, truck started to run really bad, so I performed a tune up with new wires, plugs, cap and rotor. This fixed the running problem and the new P0300 code that came up. Since I was at it, I looked at all of the lines again, that I could see, and they looked fine (no cracks and still connected). I looked for the mysterious vent valve that the Haynes manual mentioned, but there is nothing near the tank with the exception of the fuel pump and the tank pressure sensor on the pump. After looking at all of this and things seemed to be fine, I erased the codes from the computer, yes, I broke down to buy a code reader, and so far (30 miles) the P0440 has not come back. I know that it will and then the smoke machine will be in my future, but until then, thanks for all of the inputs and if it returns, I will let you all know. Thanks again.

[Austin8214]

If the code comes back agian try putting a new gas cap on it. This is a common problem

[nflskinfan]

Originally Posted by Austin8214

If the code comes back agian try putting a new gas cap on it. This is a common problem

Replacing the gas cap was the first thing that I tried, but that didn't change anything. The truck has been driven for roughly 4oo miles since I cleared the codes and it is still holding strong. I don't know what fixed it this far, but glad that the light is out and running smooth again.