DTC Decoded: P1131

Code: P1131 — Upstream Oxygen Switch Sensor Indicates a Lean Condition at Bank 1


Your Ford’s heated oxygen sensor is indicating an overly-lean condition while being monitored by the ECM.

O2 Sensor

Common Causes:

  • Faulty Oxygen Sensor
  • Vacuum Leaks Effecting Bank 1
  • Fuel Injector Issues
  • Cylinder Misfire


The check engine light is almost always the first notable symptom of this code. You may also notice hesitation in acceleration and poor fuel economy.

What the Tech Says:

When the ECM collects information from the O2 sensor and it detects a lean system, this means there isn’t enough fuel or there’s too much air in the system. The first place to check would be the vacuum system as this is the most common culprit of this issue. Also, refer to the common causes above and check those components once you have cleared the vacuum system as the culprit.