Lack of HO2S Switch — Sensor Indicates Lean (Bank 1)
2011-2015 Ford Explorer 3.5L V6
Description
The upstream heated oxygen sensor on Bank 1 is not switching and indicates a persistent lean condition. The PCM detects that the sensor is stuck indicating lean (high oxygen content) and the fuel system is attempting maximum rich correction. This is one of the most common Ford-specific DTCs, particularly on Explorer, Ranger, F-150, and Mustang models.
Symptoms
- Check Engine Light
- Rough idle
- Poor acceleration
- Increased fuel consumption
- Hesitation
- Possible misfire
Common Causes
- Vacuum leak past the MAF sensor (most common when paired with P1151)
- Dirty or faulty MAF sensor (most common for single-bank code)
- Faulty upstream O2 sensor Bank 1
- Low fuel pressure
- Leaking fuel injector
- PCV valve or hose leak
- Cracked intake manifold or plenum gasket
- Exhaust leak before O2 sensor
Diagnostic Steps
- Check for vacuum leaks — especially PCV hose from passenger valve cover to intake manifold
- Clean MAF sensor with MAF-specific cleaner
- Monitor O2 sensor switching on scan tool (should oscillate 0.1-0.9V)
- Check fuel pressure at idle (30-45 PSI typical)
- Inspect intake manifold gaskets for leaks
- Check for exhaust leaks before O2 sensor
Repair Notes
If both P1131 and P1151 are present, focus on vacuum leaks and MAF sensor. If only P1131, suspect O2 sensor Bank 1. Clean MAF first as cheapest fix.
Related Codes
Other Powertrain Codes
- P0001Fuel Volume Regulator Control Circuit/Open
- P0001Fuel Volume Regulator Control Circuit/Open
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0003Fuel Volume Regulator Control Circuit Low
- P0003Fuel Volume Regulator Control Circuit Low
- P0004Fuel Volume Regulator Control Circuit High
- P0004Fuel Volume Regulator Control Circuit High
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
P1131 on Other Vehicles
Common Questions
What does code P1131 mean on a 2011-2015 Ford Explorer?
P1131 stands for "Lack of HO2S Switch — Sensor Indicates Lean (Bank 1)". The upstream heated oxygen sensor on Bank 1 is not switching and indicates a persistent lean condition. The PCM detects that the sensor is stuck indicating lean (high oxygen content) and the fuel system is attempting maximum rich correction. This is one of the most common Ford-specific DTCs, particularly on Explorer, Ranger, F-150, and Mustang models.
What are the symptoms of P1131 on a Ford Explorer?
Common symptoms of P1131 include: Check Engine Light, Rough idle, Poor acceleration, Increased fuel consumption, Hesitation, Possible misfire.
What causes P1131 on a 2011-2015 Ford Explorer?
Common causes of P1131 include: Vacuum leak past the MAF sensor (most common when paired with P1151), Dirty or faulty MAF sensor (most common for single-bank code), Faulty upstream O2 sensor Bank 1, Low fuel pressure, Leaking fuel injector, PCV valve or hose leak, Cracked intake manifold or plenum gasket, Exhaust leak before O2 sensor.