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?