Car
: Porsche Boxster
Year:
1999
Miles:
Approx 28,000
Diagnostic tool:
Durametrics for Porsche
The car exhibited codes P1125 (Oxygen Sensing, Range 1, Cyl 4-6) and 1123 (Oxygen sensing, Range 1, Cyl 1-3).
Initially I thought these codes were indicating bad O2 sensors. This was not the case and I changed them unnecessarily.
Be sure to thoroughly research codes before doing any work.
These codes actually meant that the O2 sensors indicated that the car’s computer could not adjust the fuel air mixture to avoid over-rich condition (could not lean it out).
This can be caused by several things, including leaky injectors, vacuum leaks, or problems with the EVAP charcoal canister.
Because the car was running fine even with the check engine light on, I didn't think it was a major running component like the injectors.
Forum research revealed that similar symptoms with CEL coming back on with same codes after reset, after driving 150 to 200 miles was experienced by a member, and resolved by the replacement of the shut-off valve component of the charcoal canister.
This post describes the process of replacing this item.
Tools
:
Flat head screw-driver, needle nose pliers (for removing friction fasteners), proper socket and breaker bar for removing wheel (19mm +security bolt adapter if your car has one on each wheel), Torx-drive set, small channel locks, Philips head screwdriver,
Part Needed:
Shut-off valve for EVAP charcoal canister. I used an after-market one from Dorman (approx. $160 delivered)
The work:
Break loose but do not remove wheel lug-nuts of the right-front tire using a breaker bar and 19mm socket, and appropriate security socket adapter while the car is still on the ground.
LIFT and put the car on JACK-STANDS. Besides removing the wheel, you will need to get under it to loosen fasteners for the inner cowling of the right front wheel-well.
Once lifted and secured, remove the lug-nuts completely from the lugs and set the wheel aside
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There are a good number of friction and nut-on-stud (three of these) connectors that hold in the protective cowl in the wheel well.
I used a flat-head screw-driver and needle nose plyers to remove the friction fasteners.
Phillips head fasteners under front bumper, (there are 3) and friction fastener inset in inner-cowl part.
I risked twisting them to the point of breaking, so if you can obtain an appropriate tool for removing these, all the better.
Do not miss the friction connector behind the shock/spring. There are also connectors under the car towards the front that include friction ones, like in the well and Phillip’s head screws that connect it to the body.
The inner cowl is a big flexible plastic part, so be very careful removing it to avoid breaking. It would be terribly expensive to replace, I am sure.
While removing, make careful note of where the cowl slides and tucks into bodywork and wiggle it free.
If too much force seems to be needed, double check to be certain
all
fasteners are removed.
I missed the one behind the shock at first, but stopped when it was fighting me. After removing that last hidden fastener, I was able to work the part out of the wheel well.
One of three studs holding in the inner-cowl.
Replacing the valve:
With the inner cowl removed, you can see the EVAP canister on the left side, tucked up in the fender
Shut off valve at the top of the large charcoal canister under the gas fill tube
Fortunately, the shut-off valve is staring right at you at the top of the canister, so you do not have to remove the canister to replace the valve.
There is one electrical connector attached that uses a wire gate to lock it in place. Pry up on the wire to release, and the plug comes right off.
While the actual valve is only held into the canister via the friction of two round gaskets, there is one other safety measure Porsche used to make sure it does not vibrate out of place.
On the right side, looking at the part, there is a small, Torx-drive bolt and washer holding the part in place. It is a small Torx-drive bit, and it is important to have it mounted on a long driver-shaft to reach in to unscrew it.
Retaining Torx-drive machine screw and washer
Once the machine screw/bolt is removed, you need to get a good grip on the part to pull it out and overcome the friction of two gaskets that are on the part. I used a small set of channel-lock and was able to wiggle and pull it out.
Lightly silicone-grease the two gaskets on the part to ease installation and create a good seal.
Insert the part aligned with the guide slot, and make certain it is fully seated into the canister.
You can feel at the intersection of the canister and the metal ring on the part with your fingernail to make sure there are no gaps.
Screw in and tighten the star-drive bolt and washer to lock the new part into place. The washer is critical to actually hold the part so do not lose or forget it.
New shut off valve seated in place with retaining star-drive bolt.
Hold down Torx-drive bolt and washer in place
Electrical connector installed with wire lock-down gate lowered onto part. Try to remove it by hand to make sure it is not loose.
Finishing Up:
The last step is to reinstall the inner cowl protecting the wheel well components. You should not have to bend the part severely. Some bending is needed, but do not use extreme force.
Carefully tuck the edges into the same place you removed them from.
Try to align the three stud locations. If they are coming through their holes and everything is tucked into the fender and other spots correctly, the holes for the friction fasteners and the Phillips-head screw locations will line up.
Loosely start all three stud-mounted plastic nuts and Phillips head screws.
Next, install all friction fasteners (there should be no extras!), pressing them all into place, including the one behind the shock/spring assembly.
Finally, tighten the plastic nuts on the studs, being careful not to strip them and the Phillip’s head screws under the front bumper.
If all is ship-shape, reinstall the front wheel and hand-tighten all lug nuts with the wheel snugged up to the hub. There should be no gap between the wheel and the hub.
Tighten the lug nuts with a socket to further snug up but do not torque.
Remove jack-stands and lower the car to the floor. Torque all lug-nuts down to 96 ft lbs.
Drive car.
Conclusion:
If you guessed right on this fix based on car running well, but O2 sensor codes keep popping up, the CEL should not re-illuminate. If it does, more complex things may be happening.
