Emission Codes P0171 and P0175

Codes P0171 (Lean Bank 1) & P0175 (Lean Bank 2) are probably the two most common emissions codes we deal with on a daily basis.

The fundamental failure is that the Oxygen Sensor measured a  high oxygen content in the exhaust.
The sensor output voltage was low.

But WHY??

Is the sensor defective, or as in most cases, is there truely a high oxygen content in the exhaust??

Is there an exhaust leak scavenging outside air (oxygen) into the exhaust?

 Is there a vacuum leak?

I cannot tell you how many times I been told, "My cars computer said the Oxygen Sensor is bad".

No it didn't.

It never tells us what part to replace.

The code tells us what test failed.

P=Powertrain
0=Universal
1=Fuel System

71=Failed Test.

Air entering the engine is measured by weight.

 For every 14.6 grams of air entering a cylinder, 1 gram of gasoline is injected.

With a vacuum leak, the most common failure, air leaks around the inlet air sensor (False Air) and the actual weight  is under measure.

When that happens, the computer under delivers   fuel, causing high oxygen content in the exhaust (Lean Condition).

Vacuum leaks can sometimes be very difficult to find.

At Complete Car Care, we use compressed air & smoke to locate those hard to find vacuum leaks.

See picture and/or video.

With this big moving van, the leak was under the Intake Manifold and hard to detect.

I replace one defective vacuum hose and the engine stalling complaint was gone.

No Oxygen Sensors needed.

Good technology  and a complete diagnostic is essential to quality repairs.

Hope this helps.

Warren Parr
Owner

Complete Car Care.

Serving our community for 40 years