Code P042, Front Oxygen Sensor Signal Lean: Notes

PCM provides a .45-volt reference signal to oxygen sensor on circuit No. 412. When oxygen sensor temperature is less than 392°F (200°C), sensor signal voltage will be about .45 volt and PCM will keep system in open loop operation. When oxygen sensor temperature is greater than 392°F (200°C), sensor will rapidly swing from rich to lean, at least one swing every 2 seconds, if PCM is in good control of the air/fuel mixture.

Code P042 is designed to set if oxygen sensor voltage stays lean for more than 50.3 seconds during test conditions. Code P042 also sets when an oxygen sensor circuit fault exists giving a false lean indication, or when air/fuel ratio is actually lean due to a vacuum leak or fuel control system fault.