The check engine light came on just as I was about to climb the "grape-vine" section of interstate 5 north of Los Angeles. At a certain point, I knew the tranny would shift for "a climb", but all I got was a cough and hesitation before finally correcting itself. I got over the mountain ok and drove for another two hours before it came on.

Checked the codes and found a 1-1-3 and a 1-5-3. The first is listed as fuel injectors (short term fuel mixture too weak) and the other is for a rear O2 sensor.

My question: since the 850 can set a code for a specific injector, should I focus only on the rear O2 sensor?