Good Stft Reading on 2005 Accord 2.4
Code P0171 - System Likewise Lean: Symptoms, causes, mutual problems, diagnostic
Updated: July ten, 2021
The OBDII trouble code P0171 - System As well Lean (Bank 1) means that the engine air-fuel mixture is too lean, or there is too much air and too little fuel. Driving a car with the code P0171 can cause more damage to the engine over fourth dimension, as when the engine runs lean, the combustion temperature is higher.
Symptoms:
When an engine runs lean it lacks power and may stall when the auto is stopped at a finish sign. The acceleration may as well feel irksome. The engine may run rough at idle. If this code is caused past a vacuum leak, there might be a hissing racket coming from the engine. Read more about vacuum leaks. The engine may besides be hard to start. Another symptom of an engine running lean is when there is an engine knock or detonation (pinging) under load or when accelerating uphill.
Causes:
Common causes include:
- Vacuum leaks
- Chock-full or faulty Mass Air Menses sensor (MAF)
- Faulty PCV valve or other parts of PCV organization
- Stuck open purge valve/solenoid
- Faulty oxygen sensor
- Improperly installed aftermarket intake
- Low fuel pressure
- Clogged-up catalytic converter
How the code P0171 is diagnosed:
With a good browse tool that shows the live data diagnosing the code P0171 is fairly easy. Without a scan tool, the only mode to find the problem is to check the basics and research common issues with your particular car make, year and model. We take washed some inquiry and posted common problems for some cars, please read farther. The all-time identify to accept your machine for diagnostics is your local dealer - their technicians are factory-trained and know the mutual issues with the cars they service.
Basic checks under the hood include: is the air filter box properly closed? Does the intake kicking have any cracks? Are whatever of the vacuum lines or hoses disconnected?
If you have a scan tool, check Brusk Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) readings at idle and at higher rpms (read more about fuel trims below). Normally, both LTFT and STFT should be close to goose egg. If the STFT rises college than plus xv-20% at idle, but drops at higher rpms, most likely you have a vacuum leak. If the STFT is close to null at idle, but elevates to 15-20% at higher rpms, the problem could be acquired a faulty mass air flow sensor, clogged catalytic converter or low fuel pressure (bad fuel pump). Read more about using a scan tool here.
What is Intake or Vacuum leak?
An air leak anywhere between the engine intake and the mass air flow sensor is often called a 'vacuum leak' or 'intake leak'. Common examples of vacuum leaks include a ripped or cracked intake boot, leaking intake manifold gaskets, stuck-open up or defective PCV valve or ripped PCV hose, cracked or asunder vacuum line. Read more: Vacuum leaks: common sources, symptoms, repairs. Here are a few examples of intake or vacuum leaks:
Common problems causing the code P0171 in different cars:
Ane style to find a common problem with your make and model is to search for technical service bulletins (TSBs). For example, the Toyota Technical Service Message (TSB) EG045-07 for the 2003-08 Toyota Corolla and Matrix with the 1ZZ–Atomic number 26 engine mentions a leaking intake manifold gaskets in subfreezing temperature as a possible reason for the code P0171 along with some other codes. If the leaking manifold gasket is confirmed following the diagnostic steps, information technology must be replaced.
Many Ford vehicles, including Explorer and F150 had a mutual problem with leaking gaskets betwixt the upper and lower intake manifolds causing the codes P0171 and P0174. Ford has issued a technical service message on this issue. Another known effect in Ford vehicles is a vacuum leak from a ripped-through safe elbow on one of the vacuum lines at the back of the intake manifold. Some V6 Mazda vehicles (Tribute, MPV) also have this issue where the safe elbow at the dorsum of the intake manifold rips through, causing a vacuum leak and the code P0171.
A croaky or ripped intake kicking is a common reason for the code P0171 in many BMW vehicles.
The service message for Nissan Maxima dated March 2004 mentions replacing an air/fuel sensor every bit a solution for the code P0171. Another Ford TSB for a number of late 90-southward Ford vehicles describes a problem with MAF sensor contamination where both codes, P0171 and P0174 would appear together.
Problems with the mass air menstruation (MAF) sensor causing the code P0171 are fairly common in many vehicles. Sometimes the mass air period sensor just gets dingy and gives false air period readings causing the engine to run lean. Cleaning the air flow sensor may help temporarily; the proper repair involves replacing the faulty mass air period sensor. A mass air flow sensor can be tested with a scan tool; read more here: mass air flow sensor.
Basic machine knowledge: how the air/fuel ratio is adjusted
Fuel Trim Control diagram
In modern cars with the OBD-Ii organisation, the front oxygen sensor measures the corporeality of oxygen in the exhaust gases and provides the feedback signal to the engine computer (PCM) whether the air-fuel mixture coming into the engine is lean (too much air and too niggling fuel) or rich (too much fuel and besides little air).
The PCM adjusts the fuel supply accordingly to go on the air/fuel ratio at the optimum level, which is 14.7/1 (14.7 parts of air to 1 part of fuel).
This process is continuous: when the oxygen sensor detects also much oxygen, the PCM assumes that the air/fuel mixture is lean and adds more fuel. When at that place is too little oxygen in the exhaust (air/fuel mixture is rich), the PCM reduces the amount of fuel. In technical linguistic communication this aligning is called fuel trim.
What is Fuel Trim?
Brusk term fuel trim (STFT) In one case the front oxygen sensor is warmed up afterward a cold start, the engine estimator (PCM) starts cycling the air/fuel ratio between a little lean and a little rich. This cycling happens around one time or twice per 2d. This air/fuel ratio adjustment is called short term fuel trim (STFT). You lot can come across this cycling on the graph here: air fuel ratio (oxygen) sensor. A typical scan tool displays the STFT as a percentage with "-" or "+" in the Live Data way. For instance, if your motorcar had a small vacuum leak, you would see the STFT going up to + ten-15% at idle and dropping to + 3-five% at higher rpms.
Long-term fuel trim (LTFT) There is likewise a long-term fuel trim (LTFT), which is a long-term compensation of the base air/fuel ratio. For instance, if over time, the engine gradually develops a small vacuum leak, it makes the engine run bacteria (more air and less fuel). In a long term, the engine estimator (PCM) volition compensate this condition by adjusting the long-term fuel trim (LTFT) to add more fuel. The long-term fuel trim is also displayed equally a percentage with a "-" or "+" sign in a scan tool. For example, a long-term fuel trim (LTFT) at +5% means that the PCM has added some fuel, although 5% is considered inside normal range.
How the lawmaking P0171 is set up
If the air-fuel mixture becomes too lean and the engine figurer can no longer compensate for this condition past calculation fuel, the engine computer (PCM) turns the "Check Engine" light (MIL) ON and sets the trouble lawmaking P0171 - System Too Lean for Bank 1 and (or) P0174 - Organization Likewise Lean Banking concern 2, depending on which cylinder banking company is affected. The PCM also stores the freeze frame of the parameters (engine temperature, vehicle speed, fuel trim readings, etc.) at the fourth dimension when the code was set. Typically, the code P0171 is set when either short term fuel trim (STFT) or long term fuel trim (LTFT) adjustment exceeds a certain value (usually +25%). Read more well-nigh the freeze frame.
What does the term "Banking company 1" mean?
Bank1 and Bank2 in a V6 engine.
The terms "Bank 1" and "Bank 2" refer to a separate grouping of engine cylinders. Nigh in-line four-cylinder engines take only i bank: Bank one. In V6 and V8 engines, too every bit in some iv-cylinder engines, the engine is "split up" into two groups of cylinders; the Bank one is the 1 that includes the cylinder number one. To know which is Banking company 1 and Bank two in your car, y'all tin can expect information technology up in the repair manual or google information technology, mentioning the year, make, model and engine size of your car.
Q: What could crusade the lawmaking P0171 on 2002 Toyota Corolla? A: In the 2002 Corolla, the code P0171 is frequently acquired past a bad or dirty mass airflow sensor or vacuum leaks. Your mechanic can check for vacuum leaks and test the mass airflow sensor with a scan tool. If the mass airflow sensor is causing the lean condition, cleaning it may aid, just unremarkably, it will need to exist replaced. There also could be another reasons, but the air period sensor and vacuum leaks are the almost common.
Source: https://www.samarins.com/diagnose/p0171.html
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