A P0171 discord regulation is telling you the O2 (Oxygen) sensor in your 2002 Ford Focus has detected further yet O2 content in the exhaust stream, prompting the personal computer to turn on the Evaluation Engine ablaze. Also, check that the fuel injectors, fuel pressure regulator and fuel pump are working correctly. If necessary, use a professional fuel system cleaning kit.6. Check that the exhaust system components, exhaust manifold and front exhaust pipe, which lead to the oxygen sensor, are not loose or damaged and causing air to enter the exhaust stream leading to the oxygen sensor.
1. Visually peep the air cleaner development and construct undeniable the ducts, air filter box and connections are tight and are not absorbing additional air relevant to the throttle object and intake manifold.
2. Probation the Bulk Air Flow sensor, which is mounted on the air duct for the air cleaner action. Remove the sensor with a Phillips-head screwdriver and Disinfected it with a Bulk air flow sensor or electronic parts cleaner.
3. Eyeful for a vacuum leak. Make a visual inspection of every vacuum hose, looking for a disconnected, torn or punctured hose. A telescoping mirror will help you inspect in those hard to arrive places.
4. Check for a ruptured or defective intake manifold gasket by running the engine at idle. Spray carburetor cleaner around the perimeter of the manifold where it joins the cylinder head. If an air leak is present, you will notice an increase in engine speed as the solution is absorbed through the damaged spot in the gasket.
5. Check components in the fuel system. If you have not changed the fuel filter in more than a year, dirt or foreign particles trapped inside the filter may be restricting fuel flow. Normally, this edict shows up along drivability problems, conforming dearth of engine capability, hesitation during acceleration and still knocking noises future from the engine. There are a rare systems and components you desideratum to troubleshoot to treasure the one causing the Oxygen sensor to controversy this warning.
Instructions
7. Check the oxygen sensor for correct operation using a digital voltmeter and follow the instructions in the service manual for your particular model.
