I have a 2001 Exrursion 5.4L V8. The code P1131 comes up and it says "Lack of upstream heated oxygen sensor switch - secsor indicates lean - bank #1". I hear it could be the sensor that is bad or there is a vacume leak. It runs like a champ, no spitting, no sputtering, no missing, no ruff iddle. What do I need to do to fix it or where do i need to start looking? Thanks.

 

Copied from another ford Forum. Kudos to Phantom_Smack from fordforums.

P1130 - Lack of HO2S-11 Switch, Fuel Trim at Limit The HEGO Sensor is monitored for switching. The test fails when the HO2S fails to switch due to circuit or fuel at or exceeding a calibrated limit. Electrical:
Short to VPWR in harness or HO2S
Water in harness connector
Open/Shorted HO2S circuit
Corrosion or poor mating terminals and wiring
Damaged HO2S
Damaged PCM
Fuel System:
Excessive fuel pressure
Leaking/contaminated fuel injectors
Leaking fuel pressure regulator
Low fuel pressure or running out of fuel
Vapor recovery system
Induction System:
Air leaks after the MAF
Vacuum Leaks
PCV system
Improperly seated engine oil dipstick
EGR System:
Leaking gasket
Stuck EGR valve
Leaking diaphragm or EVR
Base Engine:
Oil overfill
Cam timing
Cylinder compression
Exhaust leaks before or near the HO2S(s)
A fuel control HO2S PID switching across 0.45 volt from 0.2 to 0.9 volt indicates a normal switching HO2S.
P1131 - Lack of HO2S-11 Switch, Sensor Indicates Lean A HEGO sensor indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time. See Possible Causes for DTC P1130

 

Thats quite a list of causes. Obviously the leaky manifolds are a common issue with these trucks, what would a few other top suspects be?

If you haven't guessed, my '99 recently popped the P1131 code, although it only happens occasionally (doesn't come back right away if I clear the codes with a scanner).

 

I got that code twice so far. Reset the pcm and it went away. I'm still considering replacing both O2 sensors but i'll likely wait to see if this thread takes off and can provide me with a bit more insight. The.last thing I wanna do is just start throwing parts (and $$) at the truck.