My Jeep is a 2000 4 Cyl, 5 speed with 98,000 miles. My son's Jeep is a 2001 4 cyl automatic with 82,000 miles. Within a 7 hour span, both "check" engine lights came on......with the same code......PO138. I believe it is for the O2 sensor after the converter. Kinda weird same code at the same time. Any thoughts?