P0174 Code – Meaning, Causes, Symptoms (& How To Fix)

A guide on how to diagnose & repair problems causing the P0174 trouble code

P0174 Code

A P0174 is a trouble code that appears when the O2 sensor on bank 2 feels that the air-fuel mixture is over its ability to correct it.

There are several possible reasons for this. Here is everything you need to know about the P0174 code.

P0174 Definition

P0174 – System Too Lean (Bank 2)

What does the P0174 Code mean?

The P0174 code means that the O2 sensor on bank 2 recognized a too lean mixture to make corrections. The O2 sensor can correct a fuel mixture of +-15%. If the needed correction is out of this range, the P0174 code will be stored.

P0174 Symptoms

The most common symptoms of the P0174 code are a check engine light and bad engine performance. You can probably experience hiccups and jerky acceleration also.

Here’s the signs of code P0174:

  • Check engine light
  • Low Engine Performance
  • Rough Idle
  • Decreased fuel consumption
  • Hiccups on acceleration

How serious is the P0174 Code?

Medium – It is nothing that is going to destroy other parts of your car immediately if you keep driving with your car.

But, in the long run, it can damage the engine’s internal parts because of the lean mixture. If you experience this trouble code, do not make full acceleration pulls. Drive carefully to the workshop and repair the problem first.

Causes of the P0174 Code

There is a lot of different things that could cause the P0174 code.

The most common cause of the P0174 code is a faulty MAF sensor or a vacuum leak somewhere. It can also be low fuel pressure-related problems like a weak fuel pump or clogged fuel filter.

Here’s a list of the possible P0174 causes:

What repairs can fix the P0174 code?

  • Clean or replace MAF sensor
  • Repair Vacuum Leaks
  • Replace Fuel Filter
  • Replace Fuel Pump
  • Replace PCV valve
  • Replace Intake manifold gasket
  • Replace O2 sensor bank 2

Common Diagnostic mistakes

A common mistake is to start replacing O2 sensors, the first thing you do, especially on the wrong bank.

Bank 2 – which this trouble code refers to is located on the side with cylinders 2, 4, 6, etc. Learn more about how to detect banks here: Bank 1 vs Bank 2.

Another mistake is to not check for intake and vacuum leaks directly.

Recommended Tools for Diagnosis

How to diagnose the P0174 Code

  1. Connect an OBD2 Scanner and look for any other related trouble codes that can lead you to another faulty part.
  2. Connect an EVAP smoke machine and pressurize the system to find any intake or vacuum leaks. Repair the leaks and reset the codes if you find any.
  3. If you do not have an EVAP smoke machine, either check visually or go to a workshop that has one. It helps the diagnosis a lot.
  4. Check the MAF sensor and clean the sensor carefully with an electronic cleaner.
  5. Install the MAF sensor again and remove the trouble codes. Continue the troubleshooting if the problem still persists.
  6. Check the values of the MAF sensor with an OBD2 scanner. If something looks suspicious – replace the MAF sensor.
  7. Connect a fuel pressure gauge to the fuel rail to check the fuel pressure on idle and driving. If you notice a low fuel pressure – replace the fuel filter or fuel pump.
  8. If you have tried everything above and the problem still persists – Check the PCV valve function and the EVAP purge control valve.
  9. If you didn’t find any problems with the PCV or EVAP Valve, it is time to replace the O2 sensor on Bank 2.

Frequently Asked Questions

Can I drive with a P0174 code?

Assuming your engine still runs acceptably fine, you can drive with the P0174 code on and finish your trip. But when doing so, don’t accelerate hard and avoid putting any heavy load on the engine. Essentially, this code means it is either getting too much fuel or not enough air. This offsets the air-fuel mixture to a degree where the ECU, which uses the sensor to measure the oxygen content, may not sufficiently adjust it anymore. As a result, the car will be sluggish on acceleration and will run rough.

How much does it cost to fix a P0174 code?

This depends on what triggered the P0174 code in the first place. In the case of a loose hose clamp or air hose, it’s just a case of putting them back on and tightening everything up. If doing by yourself, this won’t cost you anything. Cleaning the MAF sensor is a cheap fix, too, as it only needs a can of cleaner, which costs some $10. Things like broken intake manifolds, broken fuel pumps, or faulty 02 sensors are pricier and may set you back several hundred bucks.

How to clear code P0174?

Like with all trouble codes, you will need an OBD2 scan tool to clear the P0174 code. Plug it into the car’s diagnostic socket and then access the engine’s ECU module. Then, find the vehicle’s diagnostic trouble code memory and clear any codes stored here. But have in mind that if you haven’t fixed what was causing the problem in the first place, the P0174 code will come back.

Does P0174 clear itself?

No, the P0174 code will not clear itself, even after you’ve successfully repaired the broken part. Even the check engine light will probably stay on in the beginning, only to go off after several restarts. But even when this happens, the P0174 code will stay logged in the vehicle’s diagnostic memory. The only way to fully clear it is with a scan tool.

Can P0174 cause misfire?

Yes, the P0174 code can definitely cause the engine to misfire. This will happen, though, only if the mixture becomes so lean that the spark plug may not ignite it. And in this particular case, only bank 2 cylinders will suffer from this problem. If your car has the P0174 trouble code and is misfiring a lot, you shouldn’t drive it, as this could damage its engine.

Conclusion

The P0174 trouble code is set when the air-fuel mixture for bank 2 is lean to the extent that the ECU cannot compensate by adjusting the fuel trims. The ECU assesses this using a signal from the oxygen sensor.

Symptoms you may experience with a P0174 trouble code include rough idle, hesitation on acceleration, misfire, or overall poor engine performance. And as with any other trouble code, the check engine light will be on.

In most cases, the lean mixture will be caused by vacuum or boos leaks, fuel delivery issues, or incorrect MAF readings. Sometimes, the P0174 can happen because of a faulty oxygen sensor or a stuck-open PCV valve.

Magnus Sellén
Written by:

Magnus is the owner and main author of Mechanicbase. He has been working as a car mechanic for over 10 years, and the majority of them specialized in advanced car diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.

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