P1131 – Oxygen Sensor 1 Bank 1 (Ford)

P1131 Diagnosis Procedure

In a nutshell, the oxygen (02) sensors on your Ford measure the oxygen in the exhaust to determine how rich or lean the ratio of fuel and air are in the cylinders. Optimizing this mixture means better fuel economy and fewer exhaust emissions. A lean reading, such as P1131, indicates that there is too much air in the fuel:air mix.

When this code triggers:

1. Diagnosis should start with a vacuum test to determine if there are any leaks.
2. The fuel injectors for the bank 1 cylinders should be checked as well.
3. It’s a good idea to determine when the fuel filters were last changed as well, just in case the filter has become clogged enough to interfere with normal flow.
4. A check of the EGR (exhaust gas recirculation) valve should be done to determine if it’s clogged or stuck open.
5. On most vehicles, the engine idle is determined by the computer, but some will have adjustments and should be checked to make sure they are on par with the recommended settings – especially if the vehicle recently had a tune up.
6. Finally, the O2 sensor itself may be going bad, especially if it’s old. If you can’t find any other possible problems, this is likely the issue.

Replace or repair anything you find to be faulty, clear the engine code, and see if the problem is repaired.

Author Jason Lancaster is the founder of AccurateAutoAdvice.com, a website dedicated to helping vehicle owners get the right info. Jason also works with BlueSpringsFordParts.com, a company that sells OEM Ford/Lincoln/Mercury parts online at discounted prices. Learn more here.