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 – System Too Lean (Bank 2)
What does P0174 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.
The most common symptoms of the P0174 code is a check engine light and bad engine performance. You can probably experience hiccups and jerky acceleration also.
- 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 reason for 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.
- Faulty MAF Sensor
- Vacuum Leak
- Boost pipe leaks
- Fuel pump
- Clogged fuel filter
- Faulty O2 Sensor Bank 2
- Faulty PCV valve
- Intake Manifold Gasket
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 P0174 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.
How to diagnose the P0174 Code
- Connect an OBD2 Scanner and look for any other related trouble codes that can lead you to another faulty part.
- 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.
- 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.
- Check the MAF sensor and clean the sensor carefully with an electronic cleaner.
- Install the MAF sensor again and remove the trouble codes. Continue the troubleshooting if the problem still persists.
- Check the values of the MAF sensor with an OBD2 scanner. If something looks suspicious – replace the MAF sensor.
- 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.
- If you have tried everything above and the problem still persists – Check the PCV valve function and the EVAP purge control valve.
- If you didn’t find any problems with the PCV or EVAP Valve, it is time to replace the O2 sensor on Bank 2.
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Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.