I have a '98 For Ranger. After 256,000 miles, I recently had a new (rebuilt) motor put in my truck. After about 2 days of driving with the new engine, the Check Engine light came on. I went to Auto Zone and had the codes checked, and these two codes came up:
“Misfire monitor malfunction”
“Oxygen circuit slow response bank 2 sensor 1”
The guy at Auto Zone couldn’t tell me what they meant. Does anyone know - and is this something serious that needs to be checked out immediately or have anything to do with the new motor that was put in?