A P1131 fault code on a Ford vehicle generally indicates a problem with the oxygen sensor. It is a relatively common code and can set off the "Check Engine" or "Service Engine Soon" light.
The P1131 code references the oxygen sensor near the firewall of vehicles with the 3.0 DOHC engine, such as the 2003 Taurus. The code can be activated by several occurrences.
Oxygen sensors aid the engine to operate at maximum efficiency and with minimal emissions. The sensors transmit data to the vehicle's computer that controls the mixture of fuel and air. Measuring the exhaust, the sensors initiate fuel-air mixtures.
PCM Initiates Code
The Power Train Control Module (PCM) receives the data from the sensors and quickly changes the fuel mixture. If the sensors are not switching properly, the PCM initiates the P1131 code and a warning light and/or message appears advising the driver that there is a problem.
P1131 Code Causes
The P1131 code can be initiated due to a bad fuel injector, a slow sensor or a vacuum leak. Generally, the P1131 code is triggered by a faulty or failing sensor.