'02 Highlander 'check engine' light

Last summer I had a CEL (01 Prism) and I replaced the gas cap. It took several days before the CEL went out.

---MIKE---

Could be the gas cap huh? Few months ago "check engine" light also came on but after opening up the gas tank & tightened it it went away after a few hours. But why wasn't that one of the diagnoses (or however you would word it :)) if it was simply the gas cap?

take it to toyota dealer and pull the code cost $35

--------------------------------- check out my camry

A loose gas cap is the most common cause of check engine lights coming on but the trouble code has to do with the fuel tank evaporative emissions system, which wasn't one of the codes listed. The system uses 2-trip detection logic to determine whether to illuminate the check engine light (actually called a malfunction indicator light, or MIL). 2-trip detection logic means that the condition must be present or absent for 2 driving cycles so if the condition is not present any more, the MIL will go off.

The actual trouble codes would have been more helpful than the descriptions you gave because the standard On Board Diagnostics generation II (OBD II) system does not have a trouble code for large vacuum leak or engine oil leakage into exhaust valve guide seal. The OBD II codes will tell you which catalytic converter is bad (a 4 cylinder has 1 converter and a 6 cylinder has 2 converters) and will also tell you which cylinder or cylinder is/are misfiring and how severely. There is also no code for a defective converter - the code will say what the converter is not doing. A bad O2 sensor can give you a code that says that the catalytic converter operation is below threshold.

The MIL can go out because someone cleared the trouble codes when they pulled them or because the condition is intermittent (2 trip detection logic) or the condition is gone.

For now, don't worry, and if the MIL comes on again, take it to a dealer. Some emissions components are covered for up to 80,000 miles in the U.S.

The check engine light will illuminate when the process controller can not keep the fuel/air ratio within it design parameters. Something as simple as a fouled plug can be the cause. If the fault clears itself after a predetermined number of restarts, the light will go off. At that mileage a temporary glitch, like a piece of carbon, was the most likely scenario. Not to worry, if it happens again take the vehicle to a dealership for correction, WBMA

mike hunt