Meaning of the P0174 OBD2 Code
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The technical definition of P0174 code is: System Too Lean in Bank 2
This means there is too much air in the air-fuel ratio, which results in an overly lean running condition. This code is triggered by the #1 O2 sensor. Once the upstream O2 sensor detects too much oxygen in the exhaust, the ECU will try to compensate by requesting more fuel to be injected inside the combustion chamber.
However, if the ECU fails to adjust the air-fuel ratio within the specified parameters in bank 2, it will trigger a check engine light.
ThePeoplesGarage once again made a killer video on troubleshooting the “lean” codes P0174 and P0171:
What are the causes of a P0174 OBD-II code?
The interesting thing to point out is the P0174 code is not usually attributed to a sensor problem. Since this trouble code means there is too little fuel in bank 2, it can possibly be caused by a fuel delivery problem. With that being said, the code can either be triggered by a clogged fuel filter or a faulty or dirty fuel injector. A problematic fuel pump or clogged fuel rails might also be the cause of the fault.
Here’s the most common causes I’ve found for this DTC:
- Dirty or faulty Mass Airflow Sensor (MAF)
- Dirty or faulty Oxygen O2 sensors
- Failing fuel injectors
- Clogged fuel filter
- Vacuum leak
One of the first things to check is a dirty or faulty MAF sensor. Dirt, oils, sludge, and debris in the MAF sensor will make the engine think it is getting enough air. In truth, the MAF sensor is sending a false reading and the engine compensates by requesting more fuel.
But in some cases, the P0174 code is caused by vacuum leaks in the system. This can be easily observed in older model vehicles with high mileages. Smoke tests are your friend if you suspect a vacuum or exhaust leak!
What are the symptoms of a P0174 fault?
Since bank 1 and bank 2 are running in different operating conditions, you will feel a general lack of power and performance from the motor. The P0174 code will cause engine surging, hesitation, and erratic idling. Detonation or engine knocking is also noticeable especially when climbing over steep slopes or during hard acceleration.
Of course, the most obvious symptoms of P0174 code are an illuminated check engine light and poor fuel economy.
- Check Engine Light on
- Poor fuel economy
- Slow throttle response
- Rough idling
How much does it cost to fix the P0174 DTC?
Like many other codes, it depends on the source of the problem and the type of vehicle.
In some cases, this code means replacing the oxygen sensor, MAF sensor, or both. But before buying and replacing the sensors, it is better to perform the right diagnostics. This can run up to $100 just in parts.
Since the P0174 code can be attributed to a dirty or fouled MAF sensor, the wiser move is to clean the MAF sensor first before considering a replacement. Buying a can of electronics cleaner will only set you back $10 to $15.
Vacuum leaks can be fixed cheaply by replacing damaged hoses with new ones. The hard part is finding the vacuum leak, which requires special knowledge and a host of diagnostic tools.
You can expect to spend more if the problem is due to a broken or fouled-up PCV valve or clogged EGR valve. However, both parts will only cost around $50 to $80 each plus labor.