The most efficient combustion engines have an air-fuel mixture ratio of 14.7 parts air to 1 component fuel. A lean condition develops when the air-fuel mixture contains more than 14.7 air to 1 part fuel, activating the P0174 code.
A vacuum leak, which brings more air into the air-fuel mixture, or a poor fuel system, which does not inject enough fuel into the air-fuel mixture, can produce a lean state. The powertrain control module (PCM) tries to rectify the lean state by pumping more fuel into the mixture to maintain the proper 14.7:1 ratio. Code P0174 shows up when these modifications become too large.
So, what is code P0174? What causes it? How to fix it, and how much does it cost? Our blog has all that info covered!
What is code P0174?
The Diagnostic trouble code (DTC) P0174 indicates ‘System Too Lean (Bank 2).’ The P0174 engine code indicates that the air-fuel ratio in your vehicle is too lean. Before the gas in your car can combust and power your vehicle, it must first combine with oxygen. The mixture burns completely when the air and gas are present in the correct proportions. Your vehicle will not run efficiently if the mixture is too lean.
P0171 and P0174 are the error codes that show up during lean situations. P0171 code triggers when a lean condition occurs in cylinder bank 1, and a lean condition in cylinder bank 2 triggers the P0174 code. Though the Engine/Powertrain Control Module (ECM/PCM) can restore a lean situation, it can only do so to a certain extent. So, the ECM/PCM stores the P0174 code to inform the user to fix this issue.
What could cause a P0174 code?
The P0174 engine code indicates that there is an issue with the air/fuel ratio provided to your engine. Unfortunately, there are several reasons for this, ranging from air leaks and fuel injector issues to malfunctioning sensors. So it’s best to take it to a mechanic to get a professional diagnosis. The following are the most common causes of the P0174 code.
- Faulty mass airflow (MAF) sensor
- Blockage in the fuel filter and fuel injectors
- The fuel pump is getting weak
- Weakening fuel pressure regulator
- The vacuum connector or PCV line may have cracks or damage
- Defective oxygen sensor
- Issues with PCM
- Leakage in the brake booster
Symptoms of P0174 code
The following symptoms for error code P0174 may appear on your vehicle.
- Check Engine Light turns on
- Decrease in engine performance. You will feel a lack of power while accelerating.
- The engine starts to misfire
- Increase in fuel consumption
- Rough idling
- Engine stalling
Lean vehicles emit nitrogen oxide (NOx), which is harmful to one’s health and can cause respiratory problems like asthma. Running lean scenarios can also result in a misfire, which can harm the catalytic converter with raw fuel and damage the internal components of your car in the long run. If you notice any of the symptoms listed above, take your car to an expert technician at the earliest.
Is it OK to drive with the P0174 code?
Driving your car with the P0174 code doesn’t damage your car parts immediately. But, if you continue to drive with your engine running lean, it might overheat and even damage internal engine parts. Running rich is always preferable to running lean since the extra gasoline will keep the engine cool.
You may be tempted to ignore a P0174 code for a while because you don’t notice other vehicle problems immediately away. A problem with the air-fuel mixture, on the other hand, can cause serious drivability problems since your engine isn’t getting enough gasoline.
Avoid making full acceleration pulls if you see this error code. Instead, drive slowly to the workshop and diagnose the issue first. Furthermore, some of the causes of this problem may have their own potentially harmful side effects. For example, an exhaust leak can expose you to lethal carbon monoxide emissions.
How to diagnose P0174 code
It is best o quickly take your car to an expert mechanic when it shows symptoms of the engine code P0174. The mechanic will perform the following steps to diagnose the issue with your car accurately. First, you must find out the exact reason for the issue and then start to fix the repair.
- Carries out a fuel pressure test
- Inspects for leaks in the intake system and vacuum lines
- Checks for worn hoses or leaks in the valve cover
- Examines the PCV valve
- Check the mass airflow sensor using a scan tool or a multimeter
- Test the relevant oxygen sensor using a scan tool or a multimeter
Common mistakes that can happen during diagnosis
- Changing a component without determining if it is defective through testing
- Failure to inspect for tears or leaks in the intake system
How to fix the P0174 code
After diagnosis, it’s time to make the necessary fixes to get rid of this engine code. These are some steps that can fix the issue.
- Cleaning or replacing the mass airflow
- Replacing a defective oxygen sensor
- Changing the vacuum line
- PCV valve replacement
- Changing the EGR valve
- Replacing brake booster if it has leakage
- Replacing the valve cover gasket
What is P0175 code? Here’s more info!
How much does it cost to fix P0174?
The cost of repair differs based on the reason for the P0174 engine code and if it’s something you can fix yourself or require the services of a specialist. If the Positive Crankcase Ventilation (PCV) valve is connected incorrectly, the solution could be as simple as snapping it back into place. A professional repair for a vacuum leak can cost $1000 or more.
Here are some of the reasons for a P0174 engine code, as well as how much it costs on average to have it fixed by a mechanic. Of course, your pricing will differ based on your location and car type.
| Item | Estimated cost |
| Vacuum leaks | $1000 |
| Fuel pump | $1300-1700 |
| Fuel pressure regulator | $200-400 |
| Repairing exhaust | $100-200 |
| Oxygen sensor or air-fuel sensor | $200-300 |
| Cleaning MAF | $100 |
| Replacing MAF | $300 |
| Replacing PCV valve | $75-100 |
| Replacing spark plug | $150 |
| Exhaust gas leak | $300-400 |
| Defective O2 sensor | $325-400 |
How do I fix code P0174?
You can fix the P0174 engine code yourself. However, determining what’s causing the problem with your air-fuel combination might be difficult. Firstly, examine the wiring harness and connectors. Check properly to see if anything’s pushed out, broken, bent, or rusty, especially connecting pins.
Take your car to a mechanic for a complete diagnostic inspection if nothing appears to be wrong or if you’re unsure how to solve the issue. You can then determine whether the issue is something you can handle on your own. If so, you may have to do the following steps.
- Change a defective sensor.
- Replace spark plugs
- Clean the fuel injectors
- Reconnect or replace the PCV hose
Tip: If your car’s problem is severe like there is a leak in your intake or exhaust, it’s better to take your car to an expert mechanic quickly.
Can an exhaust leak cause a P0174 code?
A vacuum leak is the most likely reason for a check engine light on and P0171 and P0174 codes stored. When the car’s computer detects too much oxygen in the exhaust, it sets these codes. Lean codes are set by excessive oxygen readings in the exhaust.
Can an O2 sensor cause a P0174 code?
The code P0171 is a lean trouble code kept in the PCM for your car based on the readings from the oxygen sensor (O2). If your car activates this code, it implies that there is the presence of excess air in the exhaust.
Can a bad fuel filter cause P0174?
Yes. The code activates if your car has a clogged fuel filter or damaged fuel pump.
Can bad spark plugs cause the P0174 code?
Yes. When the code activates, your ignition may not be firing properly, which can be due to including weary spark plugs and vacuum leaks.
Can a fuel pump cause a P0174 code?
A defective fuel pump or a blocked fuel filter can cause the code to activate. The PCM continuously raises the fuel given to the combustion chambers after receiving an accurate signal from the oxygen sensor that the fuel mixture is too lean.
P0174: The bottom line
- The code appears as Bank 2 has too much air but less fuel.
- Driving the car for a long period with this condition can cause damage to internal engine parts.
- Take your car to a mechanic and repair it quickly when the code appears.
- While diagnosing the P0174 code, it is critical to complete the whole diagnostic process. A broken MAF sensor, clogged fuel injectors, vacuum leaks, and other issues can all cause this DTC to appear.
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