OBD-II Code
P1131
Severity
Not yet reviewed
Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.
Can you drive it
We cannot say
Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.
Indicative cost (USD)
$18–$1,200
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
P1131 is the Ford-specific code for Bank 1 Sensor 1 (upstream O2 on the passenger side of most Modular V8s, driver side on transverse 4-cylinders) showing a persistent lean condition without enough rich/lean switches to satisfy the fuel-trim monitor — essentially the PCM is adding fuel but the sensor never sees the mixture richen up.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then follow the diagnostic notes further down this page, in the order they are written.
They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Read the full diagnostic procedureP1131 is the Ford-specific code for Bank 1 Sensor 1 (upstream O2 on the passenger side of most Modular V8s, driver side on transverse 4-cylinders) sh…
P1131 is the Ford-specific code for Bank 1 Sensor 1 (upstream O2 on the passenger side of most Modular V8s, driver side on transverse 4-cylinders) showing a persistent lean condition without enough rich/lean switches to satisfy the fuel-trim monitor — essentially the PCM is adding fuel but the sensor never sees the mixture richen up. It is one of the most-searched Ford codes because the 4.6L and 5.4L Triton engines set it constantly.
Cheapest-first ladder
- scan live data and watch Short-Term Fuel Trim (STFT) Bank 1 and Long-Term Fuel Trim (LTFT) Bank 1 at warm idle — anything above plus-10 percent LTFT confirms a real lean condition (Ford spec is plus or minus 8 percent at idle, plus or minus 15 percent at cruise).
- Smoke-test the intake from throttle body to head with 0.5 psi shop-smoke; the usual leak is the PCV hose to the passenger valve cover on 4.6L 2V engines, or a cracked rubber elbow on the intake plenum.
- If trims are clean and no leak shows, swap the upstream O2 connector with Bank 2 (P1151's sensor) and see if the code follows — a Bosch or Denso replacement runs $45 to $90, the Motorcraft OEM is $120 to $180.
- The expensive misdiagnosis is replacing both upstream O2s when the actual fault is a $20 PCV elbow, or worse, replacing a Bank 1 cat for $600 to $1,400 based on the lean code alone.
Vehicle-specific patterns1996-2004 Ford F-150/Expedition/Crown Victoria 4.6L 2V Triton engines crack the hard plastic PCV elbow that runs from the passenger valve cover to th…
- 1996-2004Ford F-150/Expedition/Crown Victoria 4.6L 2V Triton engines crack the hard plastic PCV elbow that runs from the passenger valve cover to the intake — Motorcraft part 1L3Z-6A664-AA, $18 dealer, accounts for the majority of P1131 cases on this platform.
- 1999-2004Ford F-150/Expedition 5.4L 2V trucks add the intake manifold gasket failure (plastic manifold) and the rear-of-engine vacuum tee that crumbles — Ford TSB 06-26-3 covers the plastic intake.
- 2004-2008Ford F-150 5.4L 3V engines set P1131 alongside misfires when a spark plug blows out of the head (the infamous two-piece plug ejection); Ford TSB 08-7-6 documents the plug-blowout repair using the Lisle 65600 thread kit.
- 1997-2003Ford Escort/Focus 2.0L Zetec sets P1131 when the upper intake manifold gasket fails between runners 1 and 2.
Estimated repair$18 to $1,200.
Look up another code
More free tools