Home › Forums › Stay Dirty Lounge › Service and Repair Questions Answered Here › huge stft's, abnormally low O2 sensor voltages. PCM issue? › Reply To: huge stft's, abnormally low O2 sensor voltages. PCM issue? October 23, 2023 at 8:21 am #1026833 Rahul JonesParticipant Have you checked the oxygen sensor condition physically? I have a doubt it is covered in crud. If possible to swap, swap the downstream and upstream then check.