What are the P0171 & P0174 fault codes? Is there a reason for lean mixture failure? What are the signs and causes of poor mixture? How to fix P0171 & P0174 error codes ?….
This article will help you if the “Engine Malfunction Lamp”, or engine lamp, is on.
For closed-circuit fuel systems, the ideal mixture of air and fuel is always 14.7/1. This means that a gasoline engine will require 14.7 units of air in order to burn 1 unit (or fuel) in the combustion chamber. This ratio changes to 14.5/1 unit in diesel vehicles and 15.1/1 unit in LPG vehicles. It is known as “Poor Mixture” if the air ratio exceeds the set value. If it falls below that, it is “Rich Mixture”.
Rich Mixture = More Fuel / Less Air
Poor Mixture = Too Much Fuel / Too Little Air
An oxygen sensor is used to measure the oxygen content of exhaust gas in order to ensure that the engine runs properly. It can adjust the mixture depending on the situation by injecting more or fewer fuel into the combustion chamber.
The Electronic Control Unit is able to adjust the fuel/air mixture according to certain parameters. If the set level is exceeded, the ECU will generate an error code. The ECU is notified by oxygen sensors, which measure the oxygen level in exhaust systems and report it back to them. If the ECU is sending more fuel than usual in order to adjust the required fuel mixture, it will generate error codes P0171-P0174. The check engine light will be illuminated to inform the driver.
The code P0171/P0174 indicates that the ECU can no longer alter the air and fuel mixture. It will not be able adjust it automatically. P0171 refers the first order fault (Bank 1), while P0174 refers the second order (Bank 2). The code P0174 is usually applied to V6 or V8 engines. Because 4-cylinder engines only have one bank. This is only possible in very rare cases. Some straight 4- and 6-cylinder engines, such as BMW and Lexus, divide the cylinders into groups with two or three cylinders and call them “Banks”.
High levels of pollution are caused by vehicles that run “poor”. These vehicles are responsible for most of the asthma-causing and airborne poisons. The vehicle emits unburned hydrocarbons, (HC), to the atmosphere. Misfires also occur within the vehicle. Exhaust gases can cause eye irritation and a bad odor. Contrary to this, “Rich” vehicles have no odor (CO is odorless). The catalytic converter may emit an odor similar in nature to rotten eggs if it is exposed to too much sulfur. This smell can be detected if you’re in an SUV on a long ramp.
The P0171 code does not indicate an oxygen sensor problem. To confirm the readings of the oxygen sensors, the engine computer ran a series test.
Here are some common causes of the P0171/P0174 Fault Code
Check that the ECU/PCM software has been updated. The fuel map can become stale and start sending false information to your PCM. The fuel mixture will begin to weaken, and eventually an errors code will appear.
Vacuum leaks can be a serious problem. Vacuum leaks can be caused by a broken or ripped PCV Hose, intake manifold gasket, or loose dipstick. The PCV system includes the dipstick. Leakage can cause too much air to enter the engine. When the engine is in use, you may hear a whistling sound.
Check the EGR valve, intake manifold and gasket. It is possible that the manifold gasket may be missing for a V6 engine or V8 engine.
Common fault codes P0171 or P0174 can be caused by the Mass Air Flow Sensor (MAF). The sensor will tell the ECU that the sensor isn’t performing its task properly if it isn’t doing its job correctly. This can cause confusion for the computer as the oxygen sensors tell it more fuel is needed. Similar to the drama between a husband and wife. The MAF Sensor reported that the air was low. The Oxygen Sensor reported that the mixture was too dry. The computer attempts to correct the problem, but it returns an error.
Sometimes, the Air Flow Sensor sensing wiring can be covered with dirt, dust, oil residue and result in error code 0171. The MAF sensor can be found in the air intake pipe, just before the throttle body. Unfiltered air can enter the engine if it doesn’t fit into the air filter bowl. The dirt sticks to the MAF sensor, forming a layer. The sensor can’t do its job and is affected by changes in airflow. Fuel vapors can cause contamination of the MAF sensor. A waxy coating may form on the sensor cable from steam. While cleaning the sensor can temporarily stop problems, eventually the MAF sensor must be replaced. Clean the housing and air filter of oil and dirt. You can prevent your new MAF from crashing by cleaning and replacing the housing and filter as often as you need.
A clogged fuel filter, or a faulty fuel pumps can both cause code P0171. Although it is uncommon, The Oxygen Sensor informs the ECU that the fuel mixture is low. It then tries to increase fuel delivery to the combustion chamber. The fuel system malfunction prevents this from happening and creates a fault code.
If this is the case, it may be necessary to test your fuel pressure. If both fuel volume and pressure are normal, you can check that injectors are not sending enough fuel. Bad fuel can cause injector blockages and trouble codes.
P0171-P0174 Signs of Malfunction
- – Engine Malfunction Lamp illuminates
- – Loss of power during sudden accelerations
- – Engine misfire and knocking
- In certain cases, the driver may not notice any adverse conditions.
- – Idling problems especially when the vehicle has been stopped at traffic lights or is hot.
Causes of the P0171-P0174 Fault
- – It is possible that the PCM software will need to be updated
- – Vacuum leaks (intake manifold gaskets, vacuum hoses, PCV hoses, etc.)
- – Mass Air Flow Sensor, (MAF).
- Fuel filter obstruction
- – Fuel pump malfunctions
- Issues with faulty, dirty or clogged injectors
