I have 1999 ford f150 4.6L v6, standard 5 speed transmission, 216000 miles. Had a new fuel pump (the whole assembly ... original equipment not aftermarket) installed about 3 months ago (mid-June 2012) and changed the fuel filter as well.
Mostly I drive it only once per week ... just long enough to get everything warmed up (at least 20 minutes or so). So, since the fuel pump change I have only put about 200 miles on it.
The SES light came about 1 week ago (22 September 2012). Code reader shows P1131.
Seems to idle and run smoothly. AC on/off doesn't seem to affect it.
From what I can find P1131 indicates bank 1, upstream O2 sensor, failure to switch.
I think that is passenger side, before the catalytic converter.
Am I right so far?
I visually examined the wiring to the wiring to the sensor ... seems to be undamaged.
Given that it idles and seems to run smoothly, would you say the O2 sensor is the likely culprit? Or should I investigate other possibilities first?