Crossover owners Nissan Murano often encounter the appearance of the Check Engine indicator on the dashboard, especially after covering 150,000 kilometers. One of the most common problems is the error code P0174, which indicates a lean fuel mixture in the second bank of the engine. For V6 engines installed on this model, this is especially critical, since the engine management system cannot compensate for the excess air entering the cylinders.
Ignoring this malfunction can lead to overheating of the catalysts, reduced power and even burnout of the pistons due to detonation. You need to understand that the injection system operates in a closed loop, and if the oxygen sensor detects too much oxygen in the exhaust gases, the control unit tries to add fuel, but there is a correction limit.
Understanding the nature of this error will allow you to save significant money on diagnostics in specialized services, where parts are often changed at random. In most cases, the problem lies not in the fuel itself or the injectors, but in air leaks or a malfunction of the vacuum system, which is easy to check yourself.
The essence of error P0174 and the operation of the correction system
Code P0174 stands for “Fuel system too lean (Bank 2).” In the context of the engine Nissan Murano With a V6 configuration, "Bank 2" usually refers to the side of the engine where cylinder #1 is located, or, depending on the year and the specific engine (for example, VQ35DE or VQ35HR), the side opposite "Bank 1".
The engine control unit (ECU) constantly monitors the composition of the mixture using oxygen sensors (lambda probes) located before and after the catalyst. If the lambda probe shows that the exhaust gases contain more oxygen than expected, the ECU goes into active correction mode, increasing the opening time of the injectors.
When the correction reaches its maximum limit (usually +25% or higher) and the mixture is still lean, the system records an error. This means that too much air is being supplied and the injection system is unable to compensate for it.
It is important to distinguish between momentary spikes and a chronic problem. A short-term lean mixture can occur under hard acceleration or when the engine is cold, but P0174 only persists when the deviation threshold has been consistently exceeded for a certain amount of time.
- 🔍 Bank 2 - This is a specific side of the engine that requires a separate check of the vacuum lines.
- ⚙️ Fuel correction - a parameter that can be seen through the OBDII diagnostic scanner.
- 🌡️ Oxygen sensors — the main sensors responsible for the formation of this error.
The main causes of a lean mixture on Murano
The most common reason for P0174 to appear is Nissan Murano is a leak in the intake manifold or vacuum hoses. Air entering the engine past the flow meter is not taken into account by the system, which leads to a lean mixture. Rubber pipes become tanned and crack with age.
Another serious factor may be a malfunction of the mass air flow sensor (MAF). If this element is transmitting too little air flow, the ECU will supply less fuel than is required to burn the actual volume of air.
Often the problem is hidden in a leak in the fuel system or low pressure in the rail. A weak fuel pump or clogged fuel filter is not able to create sufficient pressure for the injectors to operate normally, especially under load.
It is also worth paying attention to the exhaust gas recirculation (EGR) system. If the EGR valve is stuck open or has a leaky seat, excess gases dilute the mixture, changing its characteristics.
- 🛢️ Fuel pump — a worn mechanism does not produce the required pressure in the system.
- 🔌 Mass air flow sensor — a dirty or faulty sensor distorts the ECU’s calculations.
- 🔧 Injector block - oxidation of contacts can disrupt injection operation.
Step-by-step diagnosis of air leaks
Begin your diagnosis by visually inspecting all vacuum pipes leading from the intake manifold to the throttle body and other components. On Nissan Murano Rubber pipes connecting the throttle body to the manifold often crack, especially in bends and near fasteners.
Use the smoke test method to find hidden leaks. To do this, the intake system is sealed and smoke is supplied inside under low pressure. Smoke coming out of any location will indicate an air leak that cannot be seen with the naked eye.
If smoke is not available, you can use a can of carburetor cleaner or propane. With the engine running, carefully spray the product around suspicious areas. If the engine speed changes (jumps or stabilizes), then there is an air leak in that area.
Pay special attention to the intake manifold gasket. On VQ series engines, gaskets lose elasticity over time and begin to leak air, especially in the area of the rear cylinders, where it is difficult to reach without removing the manifold.
- Up to 100,000 km
- 100,000 - 200,000 km
- More than 200,000 km
- I don't remember
Checking the fuel system and sensors
For accurate diagnostics, you need to connect a scanner and view the data in real time. Check the parameter Long Term Fuel Trim (long-term fuel trim) for the second bank. Values above +10% already indicate a problem, and values above +25% indicate a critical failure.
Check the mass air flow sensor (MAF) readings at idle. For a 3.5 liter V6 engine, the normal value should be approximately 2.0–3.0 g/s. If the value is significantly lower or higher at the same speed, the sensor requires replacement or cleaning.
Don't forget to check the fuel pressure in the rail. It should be in the range of 3.5–4.0 bar. If the pressure drops when running under load or does not hold after stopping, the problem is in the pump or fuel pressure regulator.
Cleaning the throttle body can also help if it is heavily contaminated with carbon deposits that are disrupting air flow. However, remember that after cleaning, a throttle learning procedure may be required through the diagnostic scanner.
☑️ Fuel system diagnostics
Stages of repair and replacement of components
If you have identified a cracked vacuum hose, replacing it is easy and inexpensive. Use only high-quality silicone hoses that are resistant to high temperatures and gasoline to avoid the problem from recurring in the near future.
Replacing intake manifold gaskets is a more labor-intensive procedure. On Nissan Murano Often you have to remove the upper part of the manifold, the throttle body and disconnect many sensors. Be sure to use original gaskets or high-quality analogues to ensure a tight seal.
In the event of a malfunction of the mass air flow sensor or lambda probe, replacement is made with original parts. Cheap Chinese analogues often have unstable characteristics, which can lead to the appearance of errors P0174 or P0171 after just a few thousand kilometers.
After performing any repair work on the intake system or replacing sensors, it is necessary to reset the ECU adaptations. This can be done through the diagnostic interface by disconnecting the battery for 10-15 minutes or removing the ECU power fuse.
Do I need to change all the gaskets at once?
If you have already removed the intake manifold, it is highly recommended that you replace all gaskets, including the injector and manifold gaskets, as old gaskets may disintegrate during reassembly and cause new leaks.
Prevention and important maintenance nuances
Replacing your air filter regularly is the easiest way to prevent lean air problems. A dirty filter restricts air flow, causing the mass air flow sensor to operate abnormally, which can lead to errors.
Use high-quality fuel with an octane rating that meets the manufacturer's requirements. Low-quality gasoline can cause detonation and clogging of injectors, which indirectly affects the composition of the mixture and the operation of the correction system.
Monitor the condition of the crankcase ventilation system. The PCV valve, if faulty, can allow excess gases into the intake, creating an air leak effect and disrupting the balance of the mixture.
When replacing intake manifold gaskets, use new sealant only in the areas specified in the repair manual, as excess sealant can get inside the engine and damage the catalytic converter.
Correctly diagnosing air leaks using smoke or carburetor cleaner will save you money on replacing working sensors and injectors.
Features of VQ35DE and VQ35HR engines
VQ series motors installed on Nissan Murano, are known for their reliability, but have their own specific weaknesses. In particular, intake manifold gaskets on these engines often fail due to thermal expansion and vibration.
On VQ35HR engines (late models), the design of the intake tract is more complex, with a system for varying the length of the intake manifolds (VIS). Failure of the VIS dampers can result in poor air flow and a P0174 code.
It is important to note that on some versions Nissan Murano The crankcase ventilation system is integrated into the valve cover. Wear of the membrane in this system can cause a stable air leak, which is difficult to find without specialized equipment.
Many owners are faced with the fact that error P0174 appears only when the engine warms up. This is due to the fact that when heated, the metal expands, and leaking connections begin to let more air through.
| Component | Symptoms of malfunction | Difficulty of replacement | Average cost (RUB) |
|---|---|---|---|
| Vacuum hose | Hissing, unstable speed | Low | 500 - 1500 |
| Mass air flow sensor | Loss of power, high consumption | Average | 4000 - 8000 |
| Manifold gasket | Air leak, error P0174 | High | 1000 - 3000 |
| Ignition coil | Misfire, vibration | Average | 2500 - 4500 |
If P0174 is accompanied by a misfire (P0300-P0306), check the ignition coils and spark plugs, as air leaks may interfere with sparking.
Conclusion and final recommendations
Error P0174 on Nissan Murano - This is a signal that the engine management system cannot maintain the correct balance of fuel and air. Most often, the reason lies in air leaks, which can be found and fixed independently with minimal tools and knowledge.
You should not immediately change expensive components, such as catalysts or injectors, without checking the simplest reasons. Competent diagnostics will save your time and money, returning your car to its former dynamics and efficiency.
Remember that regular maintenance and timely replacement of consumables is the best protection against such errors. If you are not confident in your abilities when dismantling the intake manifold, it is better to entrust this work to professionals.
Ignoring the P0174 code can cause serious damage to the engine and catalytic converters, so fixing the problem should be a priority.
Frequently asked questions (FAQ)
Is it possible to drive with P0174?
It is possible to drive for short periods, but it is not recommended. Long-term operation with a lean mixture can lead to engine overheating, pistons burnout and destruction of catalysts due to fuel burning out in the exhaust system.
How to reset error P0174 after repair?
After eliminating the cause of the error, the code can be reset using the OBDII diagnostic scanner. If you don't have a scanner, you can disconnect the battery terminal for 10-15 minutes, but this will also reset the radio and clock.
Why does the error only appear when the engine is hot?
When heated, metal and rubber parts expand. If there are microcracks in the manifold or hoses, they increase when heated, creating air leaks that have not yet appeared on a cold engine.
Does fuel quality affect P0174?
Fuel quality does not directly cause P0174, as it is an air fault. However, dirty fuel can clog the injectors, making the lean problem worse if there is even a slight air leak.
Do I need to change both lambda probes for error code P0174?
No, if the error indicates a lean mixture, most often the problem is with air leaks or the mass air flow sensor. Replacing lambda probes only makes sense if they are physically faulty or show incorrect data.