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Tuesday, October 21, 2014

Doug's Domain

Doug Vetter, ATP/CFI

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Tuesday, March 17, 2009

Another Day, Another CEL

I gave the car a much needed bath on Sunday and then topped off the tank in prep for the work week. Not far from my home during the commute Monday morning the Check Engine Light (CEL) illuminated again. I think it was at this point I mumbled to myself that BMW should have named that light "Check Blood Pressure", because every time it illuminates it means money will exit my wallet faster than an afterburner burns jet fuel, and if it's anything that irritates me more in a trying economy it's spending extra money that I'd just as soon put into my savings account.

(Image: Scan of GT1 fuel tank leak fault code page) Always the DIYer, however, I quickly donned my troubleshooting cap and realized that while it could be something related to the catalytic converters (again), that was pretty unlikely. Even I'm not that skeptical. So I began to think -- what else could the OBD system complain about that would not cause any rough running. Hmmm....that charcoal canister (that filters fuel tank vapors) is getting up there in age and they most certainly don't last forever. Then I asked myself the same question I ask when debugging software -- what else has changed recently? And then the light bulb came on -- I refueled. Could this be something as simple as a loose fuel cap?

Intent on remedying this with as little pain and suffering as possible I pulled over to the side of the road, threw on the flashers and dodged the oncoming traffic while I made my way to the far side of the vehicle to check the cap. And sure enough, I found the cap fully tightened but half latched (meaning, one of the tabs that locks with the filler collar was outside the collar flange). Relieved, I quickly refastened the cap, cursed the intelligence of the particle physicist / gas station attendant that filled my tank and hopped back in the car. As I pulled away I then pondered the question of whether the CEL would extinguish on its own now that the problem was corrected -- as it is known to do for other faults including those related to the catalytic converters.

Rather than hold you in suspense I'll tell you the answer is NO. A fuel system leak fault is permanent and must be cleared with appropriate diagnostic equipment. And there is no threshold with this fault -- if it happens once it will illuminate the CEL. This morning I brought the car into the dealer to have my tech pull the codes and the result was what I expected (see picture). Best of all, it didn't cost me a thing, and I even got to chat with a cute girl in the showroom while I laid on the floor under a new M3 analyzing how easy it would be to work on. I think she thought I was a little crazy. She was probably right.

Moral of the story? If you are forced to tolerate full service gas stations or are simply one of those lazy people like me who've become used to full service stations and don't want to get out of the car, just take the 30 seconds required to check the cap yourself and avoid this headache.

Mileage: 173900