SES light came on, lw300 - update

Aug 30, 2004 2 Replies
O

All is good now. Cleaned the evap vent solenoid and reinstall. Didn't have a scan tool so removed the battery cable for a minute to reset everything. Had to re-enter all radio stations and clock but other than that, no problems. Been driving for several trips now and SES light is still off. Oppie


Evap canister is mounted on top of the gas tank "to make it tamper
> resistant" according to the manual. If service is needed on
> this, you have to pull the intermediate exhaust pipe and drop the fuel tank.
> No nice service doors from topside :-((
>
> Evap canister vent solenoid is mounted behind the fuel door. I think that
> the valve had picked up a bit of dirt and was sticking open. There is a foam
> filter on its inlet but the housing was choked with dust. I have to question
> the sensibility of putting a vent behind the wheel well, especially the

rear wheel. With the vent


circuit pinched off, the tank seems to hold pressure. Cleaned the filter and
> blew out the valve with air. Reset the code and will see again if the code > gets set.
>
> There is also a pressure sensor similar to a MAP sensor mounted on the fuel
> tank. It is used in the evap diagnostics where the vent solenoid is
> energized to close it and the purge solenoid is energized to open it. A
> vacuum should be pulled in the tank and then the purge turns off to hold the
> vacuum. The sensor measures the rate of decay of vacuum in the tank to
> determine if all is ok or the magnitude of the leak.
>
> I have started annotating all the drawings in the shop manual similar to the
> way my Ford and Chrysler manuals were done. Much easier to follow that way.
> This is my first GM vehicle since I owned a '54 Olds 88 back in '65. >
> Oppie
>
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B

What was coating the evap vent solenoid? I wonder if that injector cleaner you put in could of had anything to do with it.

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O

No, it was very fine dust that had accumulated and was jamming the solenoid plunger.

In years past, the canisters with both solenoids were usually mounted in the front fender. Unless you were driving behind another vehicle that was kicking up dust, the vent pretty much got clean air. My L-series on the other hand, puts the vent solenoid in the rear wheel well where it gets the dust kicked up by front and rear wheels. Not too smart...especially since the normal operation is to pull a small air flow from the vent through the canister and into the tank. This pulls the vapors out of the canister and burns them in the engine but it also allows a quantity of dust to enter the fuel system.

Once I made an initial diagnosis, it took about a half hour to loosen the fuel fill and rotate it to a point that I could get access to the vent solenoid, remove, clean and reinstall the solenoid/filter.

Being the suspicious type, I couldn't help but wonder at the ses light coming on at 50,235 miles. This is just over the mandatory emissions warranty. Below 50K miles, the dealer has to pay for any emissions related failures. With computers, you can do such creative things. No accusation, just an interesting observation.

Oppie

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