Upon revving up your BMW, you could see that your engine light is on, and that could be a result of multiple issues. To figure out what’s wrong, the very first thing that should come to your mind is doing an OBD2 scan. This onboard diagnostics tool gives you a diagnosis report that consists of error codes after the scan. However, it’s upon you to learn how to diagnose and clear the codes.
If you own a BMW, then the P0174 BMW code is one that you may see often. So that you know how to deal with this code, and clear it up, in this article, we’ll be explaining what it means, how to diagnose it, fix it, and more!
P0174 BMW Code: What Does it Mean?
Like a lot of ‘P’ related codes, you will see after performing an OBD2 scan; the P0174 BMW also concerns the air-to-fuel ratio of the fuel-air mixture. In a BMW, when the Engine Control Module (ECM) detects that there is a lean condition, the engine light will turn on.
If there are small changes to the fuel-to-air ratio, then the engine control module can fix it. However, when the ratio is off by a lot, then it cannot fix it by itself, and thus it displays the P0134 error code. To be specific, the P0174 code signals that the fuel on the left bank, as in bank 2, is too lean.
Why Does a P0174 Code and Running “Too Lean” Matter?
You might know what it means to have a too lean condition, but if you didn’t, here’s a brief description for you. It essentially means that too much air has been mixed into the fuel mixture, so the car doesn’t run on the mixture with the optimum fuel-air ratio.
Running your BMW with a lean fuel mixture can cause a significant drop in your car’s performance and will cause the car to have a jerking motion. This may also result in damaging your precious car components like burned valves. Overall, there will be more friction between the parts, which will make the parts wear out quicker as well.
However, if you follow everything we say below, you should get to the root of the error code and clear the code along with all the issues causing it.
Symptoms
If you think your BMW may display the P1074 code after an OBD2 scan, then you should look out for other symptoms as well. The symptoms of this code may also apply to other ‘P’ as in powertrain-related trouble codes such as P0300 BMW, and intake camshaft position timing P0012 BMW code.
Engine Light on the Information Display Will be Lit
This symptom is already known to you, as we have mentioned it right at the beginning of the article, but we still thought it should be included in this list. Remember, just because the engine light is on doesn’t necessarily mean that you have the P0174 error code, as it could be P0304 BMW trouble code as well. So, you have to do the OBD2 scan to check.
Lacking Power
If you are a car enthusiast, then you will be able to tell that something is not right seconds after you have pressed the gas pedal down. The degradation of the engine power is certainly noticeable to the average driver as well, and it is a genuine concern. Additionally, when trying to accelerate, you will notice that the vehicle is doing it very slowly. The same thing happens with the P0172 BMW code also.
Rough Idle
When the fuel mixture becomes too lean, then the vehicle will have a very rough idle. This means that your car will be vibrating a lot when you start it. It can be a very unpleasant feeling and may cause issues like nausea for some. If you look at your RPM counts, then they will be very inconsistent as well, and if the idling is too rough, then you might start hearing sounds as well.
Misfiring of Engine
Your BMW may misfire and have difficulty starting if issues causing the P0174 trouble code exists in your vehicle. In severe cases, you might see that the car isn’t starting regardless of trying multiple times.
Engine Stalling
There are two main reasons why your engine may stall, and they are if the fuel-to-air ratio is off and if the spark plugs are faulty. In today’s case, the reason is certainly the air/fuel mixture. By engine stalling, we mean that it will slow down and will probably come to a stop without any warning signs.
We hope you notice the other symptoms before the engine stalling, or else you could be stuck in the middle of nowhere!
P0174 BMW Code Possible Causes
There’s always a reason behind an error code, and only on very rare occasions will they pop up because of a glitch in your car’s computer system. Learning all the possible causes may help you recognize the issue quicker, and in this way, you will also be able to avoid it in the future.
Keep in mind that these causes that we have discussed below are often the causes of other codes as well, so when clearing it, you may also clear some related codes.
Malfunctioning Mass Air Flow (MAF) Sensor
You will see that numerous error codes in your BMW are showing up after the OBD2 scan because of the mass airflow (MAF) sensor not working properly. This sensor measures the volume of air that is entering the cylinder of your car. Upon becoming faulty, it might let too much air into the cylinder.
As a result, the fuel mixture will become too lean, which will be detected by the ECM, and then the P0174 code will pop up. Besides the MAF sensor being faulty, this issue could also be caused if you don’t do the regular maintenance of your BMW and the sensor gets very dirty.
Heated Oxygen Sensor Not Functioning Properly
From its name, you may be able to tell that this sensor is responsible for measuring the volume of oxygen that is allowed to dissolve into the fuel mixture. When this sensor is unable to function properly, then the amount of oxygen that is given into the mixture will be off.
If your BMW shows the P0174 code, then it means too much oxygen is in the mixture. The volume of oxygen and air are proportional to each other, so if too much oxygen is in the mixture, then it also means that the mixture is too lean.
Air Leak
There could be many places where you can get an air leak, and this could be the cause of this error code as well. If there are any breaks in any hoses or any parts are very loosely fitted, then there could be such leaks. Some common ways you can get an air leak are if the intake boot gets torn and if the intake manifold gasket has become defective.
Another common source of air or vacuum leaks is leaking PCV (positive crankcase ventilation) valve. Often time the ends of these hoses will become loose as the car runs, which will let more air get into the system.
Weak Fuel Pump
It is the fuel pump’s job to deliver the fuel at a certain pressure, but if it is defective, then it will be weak, and the pressure of the fuel delivery will be below. This may also be the cause of the lean condition of your BMW.
Clogged Air Filters or Fuel Injectors
With time a lot of dust and dirt gets stuck in the air filters and fuel injectors. If you don’t get it out of these parts, then they will eventually be blocked. This is another reason why too much air may be fixed into the fuel mixture and thus make it lean.
What is the Cost to Diagnose the P0174 BMW Code?
Since we’re talking about the cost of diagnosis in this section, so you won’t have to consider any cost of parts you may need for replacements or repairs. You may be able to tell that diagnosing this trouble code can be complicated, so it’s best if you take it to a mechanic workshop.
This is an hour-long job usually, and it’ll rarely take mechanics about 2 hours to do it. Although the cost of the mechanic will vary significantly depending on several factors, the average cost will be at least $70 but will not exceed $150.
Common Misdiagnosis
The most common misdiagnosis done by mechanics is when they replace plenty of parts without even checking if they are faulty. Some mechanics often do this so they can just get more money from you, so always ask them for reasoning before they start replacing parts.
Most commonly, the oxygen sensor and MAF sensor are replaced because they are common sources of this error. However, it may be that the P0174 code in your BMW has come up for a different reason, such as leaks, which leads us to the second misdiagnosis.
As we have described above, mechanics go for replacements almost immediately, but they don’t check for other sources of the P0174 code. Oftentimes, causes such as air/vacuum leaks are overlooked. In which case, even if you replace the sensors, the trouble code will remain.
How to Fix P0174 BMW Code
Before you go ahead and make any repairs, you will have to diagnose the P0174 to see what’s causing it. From all the possible causes that we have listed above, you will have to check each one of them.
Some commons tests that you have to run for diagnosing this code are a fuel pressure test, smoke test to detect leaks, and MFA and O2 sensor test with a multimeter or scanner. The smoke test will help you find the source of the leak or breakage, but like every other test, this one should also be done by a mechanic.
Close inspection of components such as the PCV valve, EGR valve, brake booster, and cover gasket is necessary to check whether any replacements are necessary. You should also check whether your air filters or fuel injectors are clogged or not. While cleaning them might be possible, sometimes the easier option would be to just get them replaced.
After the diagnosis has been completed, you should know what replacements and repairs are needed. For leaks, you may have to tighten the hoses, and if the hoses are broken, they will need to be changed. Malfunctioning sensors generally need to be replaced, but sometimes repairs may be possible.
Final Words
Dealing with the P0174 BMW code is not easy, and you want to clear it up as soon as possible because you don’t want your car to get damaged. However, for the most part, you won’t have to stress about the diagnosis and repairs because your mechanic should be able to handle all that.
One thing that will be your replacement is checking whether the replacements your mechanic is doing are genuinely needed or not. Furthermore, ensure that they are checking all the possible causes of the P0174 before moving ahead to replacements.
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