Some 2006-07 Suzuki Forenza and Reno models may turn on the Check Engine light and log trouble code P0133 (front O2 sensor slow response time) in computer memory.
If scoping the sensor doesn't reveal anything out of the ordinary as far as response time, the code is most likely bogus and due to software issues in the PCM. Reprogramming the module with updated software is the only reliable fix. Check with a dealer for the specifics of the flash.