Nope, the check engine light never came on. Their explanation for this was that the computer only allows a problem to trigger the check engine light after multiple malfunctions. For some reason the sensor wasn't faulting enough to register although the performance issues were obvious. After enough complaining, including calling the owner of the dealership directly, they agreed to supply an identical 2001 GS300 from their pre-owned lot for back to back driving comparisons - this was the only way we were able to convince the service rep that there was a problem!!!!