Possible causes

– Faulty Oxygen Sensor
– Vacuum leak affecting bank 1 only
– Fuel injector problem bank 1
– Check for cylinder misfire on bank 1
– Engine mechanical condition

Tech notes

Though the Oxygen (O2) sensor, the Engine Control Module (ECM) has detected a lean system, which means that there is either not enough fuel or and excessive amount of air in the system. Start by checking for vacuum leaks.

When is the code detected?

The Engine Control Module (ECM) detected bank 1 oxygen (O2) at its lean limit

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1131 FORD Description

A Heated Exhaust Oxygen (HO2S) sensor indicating rich at the end of a test is trying to correct for an over-lean condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time.

FORD Technical Service Bulletins for P1131 code