My check engine light stays on in my vehicle inspite of replacing the part/S diagnosed in the diagnostics.

- Acworth, GA, USA

Check engine light on my 2000 Toyota Corolla lit up shortly after I purchased the car in May 2003. I brought it back to the dealership 3 times - they dismissed it as a minor problem all 3 times and simply reset the light. Each time, the light would light back up within several days. In September 2003, I brought it to a local mechanic, who informed me that the charcoal canister (adjacent to the fuel tank, part of the fuel system, used to gauge fuel vapors) needed replacement, since some gas spilled into it. The job was done (~$300), but the light came back in a couple of weeks. I brought the car to a Toyota dealership in June 2004, because it wouldn't pass inspection with the check engine light on. The mechanic informed me that the charcoal canister was the problem, "probably because somebody topped the tank off while filling up." He added that the charcoal canister not only had fuel in it, but was, in fact, "filled with gasoline." The local mechanic, once again, did the job (~$300). The light came back within two weeks. I never top off the tank when I fill up. My research has provided some limited answers: Charcoal canister is located very close to the fuel tank. Usually, the codes returned by the car's computer are evap control system malfunction evap control system incorrect purge flow evap control system vent control circuit malfunction which point to a problem with the switching valve that vents the canister. If the valve doesn't work, the canister isn't vented and enough fumes collect to cause the canister to stop functioning. Many others have this problem. Toyota does not seem to have any explanation about this, nor has the company taken any action. Meanwhile, to get my car back into "good standing, " I'm looking at yet another ~$300 bill.

- Worcester, MA, USA