Engine Code p0174 Meaning, Causes, Fixes (4-Step Guide)

Are you wondering how to solve that pesky P0174 code?

You're in the right place!

In this guide, you'll learn:

  • What the P0174 code means
  • How to diagnose a P0174 code
  • How to fix a P0174 code

And much more!

Engine Code p0174 Meaning, Causes, Fixes (4-Step Guide)

The p0174 diagnostic trouble code means that the engine is running a lean mixture, or has too much air in the air/fuel ratio in cylinder bank 2. You may also notice the p0171 code on the diagnostic scanner in some cases. 

This is one of the most common OBD-II check engine light error codes that occur on a vehicle, and it requires that you inspect multiple parts of the engine.

So, when you see this engine code on a scan tool, you can assume one of two things:

  • The engine isn't getting enough fuel


  • There is too much air inside the combustion chamber

Fire that scan tool up and turn the key to position two without starting the vehicle; It's time to figure out why!

What Does The p0174 Code Mean?

This means that there is too much oxygen in the exhaust. It's a lean code that informs the technician that the engine is not getting the right amount of fuel and air mixture.

What Caused The p0174 code (Possible Symptoms)?

When your vehicle has a lean condition, the O2 sensor measures too much air and tells the powertrain control module to adjust the fuel trim. 

Here are some possible causes as to why a vehicle would set off the p0174 code:

  • vacuum leak 
  • damaged intake manifold gaskets 
  • bad PCV(positive crankcase ventilation) valve
  • failed fuel pressure sensor/failed fuel pressure, the regulator
  • bad MAF sensor
  • fuel filter clogged/low fuel pressure
  • failing fuel pump
  • dirty fuel injectors
  • bad engine control module(in rare cases)
  • exhaust leak

Here are some symptoms of the p0174 code:

Read More >> What Do You Do About The Service Engine Soon Light?

How To Diagnose A p0174 Code?

Diagnosing this p0174 code requires checking over a few different components. 

Use any other engine codes stored in the PCM to direct you in the right direction. For example, if you have the p0174 code, and there is also a p0101 code set off by the mass airflow sensor, you will be able to pin down the problem easier. 

This can be a tricky code to diagnose, but with a little patience, you should be able to take care of the issue.

Step 1 - Clean the MAF(Mass Air Flow) Sensor

One of the most common reasons this code comes up is because the MAF is malfunctioning and needs to be cleaned/replaced.

The mass airflow sensor is what gives the ECM a reading of how much air is going into the engine.

If the MAF is malfunctioning, the ECM will not know the right amount of fuel to inject. 

Remove the MAF sensor, and clean it with a MAF spray cleaner that you can find at any auto parts store. 

And while you're close to the air filter, pull it out and make sure it's in good shape and mounted properly.

Step 2 - Check PCV Valve 

Locate the engine's PCV valve by referring to the vehicle's owner's manual.

Inspect the valve and look for signs of cracks/breakage.

 Remove it if needed. PCV valves rattle when shaken. 

With the engine running, remove the oil cap and place your palm over it. With a good PCV valve, you will feel suction on your palm.

You could also remove the PCV from the valve cover and place your finger over it to feel if it is sucking air. 

Step 3 - Look For Vacuum Leaks

An easy way to look for vacuum leaks in the intake manifold is by spraying soapy water around the gasket and looking for air bubbles while the engine runs.

 Visually inspect and go through the system of vacuum hoses using your vehicle's service manual as a reference; make sure they are all in good condition, all hooked up and in the correct place.

A smoke test is another sure way to find any vacuum leak. Vacuum systems have air running through them.

So, if you close off the system and run smoke through it then small leaks are easily detectable.

You can test the intake manifold for leaks by removing the airbox and running the smoke directly through it. 

Most local auto shops have a smoke tester in their set of tools, so you're either going to have to sweet talk the manager into letting you use it, or pay for a professional diagnosis.

Step 4 - Check Fuel System

Fuel pressure test

You can use a fuel pressure tester to see if the fuel pump is providing the engine with the proper PSI of fuel. 

To locate your vehicle's fuel pressure port, trace the fuel lines back from the injectors.

There should be a Schrader valve somewhere on the fuel rail that allows you to hook up a fuel pressure tester.

You can also check the fuel pressure regulator by removing and inspecting it. If it is leaking gas, or if one of its seals is broken, then it's time to replace it. 

Refer to the vehicle's owner's manual for what the acceptable fuel pressure is. You may end up replacing a fuel filter or fuel pump.

Clean/replace fuel injectors 

Dirty fuel injectors may also be the cause of this engine code. If the vehicle has more than 100k miles it is likely due for a new set of injectors.

There's no way to know if the fuel injectors are dirty without taking them out and seeing for yourself.

Read More >> What Does The P0420 Engine Code Mean?

On-Board Diagnostic systems (OBD and OBD-2) were only made standard in 1996. Every car from that point onward used an OBD system for easier fixes.

How Do I Fix A p0174 Code?

You have now successfully diagnosed the reason why the p0174 code was stored, and why the check engine light illuminated on the dash fo the vehicle. 

Now it's time to make the appropriate fix for the cause at hand. 

Remember, sometimes when you are fixing a car you replace a part that didn't need to be replaced. 

That's okay. You can always return parts that you didn't need after the fact. The more important objective is fixing the vehicle and getting the check engine light to turn off. 

Potential Fix 1 - Replacing The MAF

Replacing the MAF is relatively easy on most vehicles. It sits directly in between the air filter box and the intake manifold.

On most vehicles, you simply have to remove a couple of clips, the electrical connector to the MAF, and free it from the two hoses on each side. 

After have replaced the MAF, reset the check engine light, and check the results.

The worst thing that can happen if the problem wasn't the MAF is you returning the newly purchased sensor to the auto parts store for a refund.

Potential Fix 2 - Replacing The PCV Valve

So, you found that the PCV valve is broken or clogged. Your options are to clean it or replace it.

You should probably replace it, but you can clean it by immersing it in carb cleaner if needed.

After you have replaced the PCV valve, reset the check engine light and check the results. 

Potential Fix 3 - Replacing Vacuum Leak/Intake Manifold Gasket

You found a vacuum leak. 

For intake manifold leaks: sse your vehicle's service manual steps for removing the intake manifold if necessary. Every vehicle is different. Clean the two mating surfaces, replace the gasket, and torque it to spec.

Small vacuum lines are easy to replace, for the most part. Just disconnect its fastener(if it has one) and pull it off, or simply pull to disconnect. 

Reset the check engine light to verify that you have fixed the problem. 

Potential Fix 4 - Fixing A Fuel Problem

The first part you should replace if you find bad fuel pressure is the fuel filter. That's because this is the cheapest part, and it's a part of your general vehicle maintenance. 

Next, go for the fuel regulator. 

If that doesn't fix the bad fuel pressure problem, replace the fuel pump.

Reset the check engine light.

Good luck with your vehicle repair, and remember to ask us here at Proper Mechanic if you have any questions concerning your vehicle/engine repair!

About Your Mechanic

About Ryan Nichols

Ryan here! My pro mechanic career began as a technician for Mercedes-Benz. After two years of that great experience, I went out on my own in both the automotive and construction fields. I've since pulled my share of salvage yard parts and fixed more vehicles than I can count.

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