Owners of brand cars Nissan, equipped with QR and MR series engines, often encounter a "Check Engine" warning light and code P1171. This error indicates a discrepancy in the operation of the engine management system, namely the fuel mixture in the first row of cylinders is too rich. When the computer detects this failure, it understands that more fuel is being supplied than is required for ideal combustion, which leads to overconsumption and contamination of the catalyst.
Ignoring the problem can lead to serious consequences: from increased fuel consumption and loss of power to the failure of expensive exhaust system components. Owners Nissan Qashqai, Teana or X-Trail you need to understand that the code P1171 - this is not just a random electronic failure, but a signal of a real mechanical or electronic defect. Timely diagnostics will help avoid major engine repairs and costly replacement of the catalyst.
What does code P1171 mean and how does the system work?
Code P1171 stands for Fuel System Too Rich Bank 1. The electronic control unit (ECU) constantly compares data from the oxygen sensor (lambda probe) and the calculated amount of air entering the intake manifold. If the lambda probe shows low voltage (rich mixture) for a long time, and the ECU has already tried to reduce the fuel supply, but the result was not achieved, an error is recorded.
In modern engines Nissan a complex feedback system is used. The control unit attempts to adjust the air/fuel ratio through fuel trims. If the correction is outside the permissible values (usually -25% and below), the system understands that the fuel is being supplied in excess. This occurs during engine operation when feedback is active, that is, when driving with a moderate load.
It is important to understand that row 1 (Bank 1) is the side of the engine where the first cylinder is located. On in-line engines such as the QR25 or MR20, this is the entire system as there is only one cylinder bank. The problem may lie in incorrect sensor readings, physical fuel leaks or problems with the air supply.
⚠️ Attention: Long-term operation of a vehicle with error P1171 can lead to overheating and melting of the ceramic honeycomb of the catalytic converter due to the burning out of unburnt fuel in the exhaust system.
Main causes of malfunction
Reasons for the appearance of the code P1171 can be divided into two large groups: problems with air supply and problems with fuel supply. Most often the culprit is mass air flow sensor (DFID), which overestimates the amount of incoming air, causing the ECU to inject more fuel.
Another common cause is faulty fuel injectors. If one or more injectors cannot completely shut off the fuel flow (they are stuck or have mechanical wear), overflow occurs. It is also worth paying attention to the high-pressure fuel pump (HPF) on diesel versions or the fuel pressure regulator on gasoline versions, which may not be able to maintain the required pressure.
Problems with the oxygen sensors cannot be ruled out. If lambda probe dirty or defective, it may transmit incorrect information about the composition of the exhaust gases. In rare cases, the problem is a vacuum leak in the intake tract, which throws off the ECU's calculations, although more often it causes a lean mixture rather than a rich one.
- ❌ Faulty mass air flow sensor (MAF/MAF)
- ❌ Sticking or overflowing fuel injectors
- ❌ Faulty oxygen sensor (lambda probe) or its wiring
- ❌ Dirty fuel filter or pressure regulator
Symptoms and behavior of the car when there is an error
When a malfunction icon lights up on the instrument panel, the driver may notice a change in the vehicle's behavior. One of the most obvious symptoms is increased fuel consumption. The car begins to “eat” gasoline much faster than usual, since the ECU is forced to enrich the mixture, trying to compensate for erroneous data or due to overflow of injectors.
The second sign is unstable engine operation at idle. The engine may oscillate, vibrate, or stall when stopped. In some cases, there is a loss of power during acceleration: the car becomes sluggish and responds to the gas pedal with a delay. This is due to improper combustion of the mixture, which does not produce the required torque.
Sometimes black smoke may come out of the exhaust pipe with the smell of unburned gasoline. This is visual confirmation that the fuel does not have time to burn in the cylinders. There may also be a strong smell of fuel in the cabin when the engine is running, which requires immediate attention, as this is a fire hazard.
⚠️ Warning: If you smell a strong smell of gasoline in the cabin or see black smoke from the exhaust pipe, stop immediately and turn off the engine to prevent a fire.
- Check Engine light came on without symptoms
- Increased fuel consumption
- Loss of power and vibration
- Black smoke from the exhaust
Diagnostics: step-by-step testing algorithm
The first step in diagnosis is to scan the system using a professional diagnostic scanner. It is necessary not only to read the code P1171, but also look at “live” data. Pay attention to the fuel trim parameter (Short Term Fuel Trim and Long Term Fuel Trim). If the reading is negative and close to -25% or lower, it confirms the mixture is rich.
The next step is to check the mass air flow sensor. To do this, you can disconnect the mass flow sensor connector while the engine is running and look at the change in speed and parameters. If after disconnecting the error does not disappear or the behavior of the motor has not changed dramatically, perhaps the sensor is working and the problem lies elsewhere. Also visually check the sensor itself for contamination.
It is important to check the operation of the fuel injectors. For this, the “glasses” method or bench testing is often used. If an injector leaks when the engine is off (after releasing pressure in the system), it requires replacement or flushing. Don't forget to check the fuel rail pressure with a pressure gauge.
- 🔍 Check fuel trim parameters via diagnostic scanner
- 🔍 Visually inspect the air flow sensor for dirt and damage
- 🔍 Measure the pressure in the fuel system and check the regulator
- 🔍 Carry out a fuel leak test from the injectors (residual pressure test)
☑️ Quick diagnostic checklist
Table of probable faults and their impact
To systematize the troubleshooting process, it is useful to compare symptoms with possible causes. Below is a table that will help you quickly identify the problem and determine repair priorities.
| Malfunction | Effect on the mixture | Probability (P1171) | Difficulty of repair |
|---|---|---|---|
| Mass Air Flow (MAF) Sensor | High air readings | High | Low |
| Fuel injectors | Fuel overflow | High | Average |
| Oxygen sensor (Bank 1 Sensor 1) | Incorrect mixture composition signal | Average | Average |
| Fuel pressure regulator | Increased pressure in the ramp | Average | High |
| Faulty wiring or ECU | Control signal failure | Low | High |
What should I do if P1171 comes back after a reset?
If you have cleared the error codes but they return after a short time, this means that the problem is permanent. It is necessary to carry out in-depth diagnostics, since a simple reset does not eliminate the cause. Perhaps the problem is mechanical wear of the injectors or critical contamination of the mass air flow sensor, which cannot be restored.
Elimination methods and repair work
The simplest and often most effective method is to replace or clean the mass air flow sensor. Use a special cleaner for the mass air flow sensor, but remember that mechanical cleaning does not always help if the sensitive element of the sensor is worn out. In such cases, replacement with an original one is required. Nissan or a high-quality analogue.
If the problem is in the injectors, they must be removed and sent for professional cleaning on an ultrasonic stand. This often restores seal and spray. If cleaning does not help or the injectors have significant wear, their replacement is inevitable. Use only proven parts, as cheap analogues can quickly fail.
In some cases, it is necessary to replace the fuel pressure regulator or the fuel pump itself. This is a more labor-intensive job that requires draining the fuel and removing the tank or fuel rail. After carrying out any work, be sure to reset the ECU adaptations and carry out a test run to make sure there is no error.
Before replacing sensors, always check the integrity of their connectors and wiring. Oxidized contacts can give the same symptoms as a faulty sensor, but repairs will cost several times less.
After repair, do not forget to carry out the ECU training procedure. Some models Nissan This is done automatically after several startup cycles, but sometimes a forced reset of adaptations is required via the diagnostic interface. Make sure that the error does not return after several days of operation in different modes.
Main idea: In 80% of cases, error P1171 is solved by replacing or cleaning the mass air flow sensor, but problems with the fuel system should not be ruled out.
Prevention and maintenance tips
To avoid the error reappearing P1171, change the fuel filter regularly. Dirty fuel is the main cause of injector contamination and sensor failure. By car Nissan With a mileage of more than 60,000 km, replacing the fuel filter should be a mandatory procedure.
Monitor the quality of gasoline. Refuel only at reputable gas stations, as low-quality fuel contains impurities that can clog injectors and damage oxygen sensors. Using fuel additives to clean injectors can be helpful, but only if they are recommended by the manufacturer.
Regular diagnostics of the engine management system will help identify problems at an early stage. Even if the “Check Engine” is not on, once a year it is worth checking the fuel trim parameters and the condition of the sensors. This will save you money on costly catalytic converter or engine repairs in the future.
- ✅ Change the fuel filter every 40,000 – 60,000 km
- ✅ Use only high-quality gasoline with an octane rating recommended by the manufacturer
- ✅ Carry out engine management system diagnostics once a year
- ✅ Avoid using questionable fuel cleaning additives
Is it possible to use non-original sensors?
Using non-original sensors is possible, but requires caution. Cheap analogues often have a shorter resource and can produce incorrect data, which will lead to new errors. It is better to choose proven brands that specialize in Japanese cars.
Frequently asked questions (FAQ)
Is it possible to drive with error code P1171?
Technically it is possible to go, but it is not recommended. Operating with a rich mixture leads to excessive fuel consumption, fouled spark plugs and, most importantly, rapid failure of the catalytic converter. Replacing a catalyst costs significantly more than repairing a sensor or injector.
How to reset error P1171 after repair?
To clear the error, use a diagnostic scanner and select the “Clear Codes” function. If you don’t have a scanner, you can try disconnecting the negative terminal of the battery for 10-15 minutes, but this is not always effective, since the ECU can store the error in permanent memory. It is better to use professional equipment.
Does P1171 change to P0171?
Yes, these are different codes. P1171 is a "rich mixture" (too much fuel) and P0171 is a "lean mixture" (too much air). If you cleaned the mass air flow sensor, but the error changed to P0171, this may mean that the sensor is now underestimating air flow, or there is an air leak in the intake manifold.
Does P1171 affect vehicle inspection?
Yes, the presence of an illuminated Check Engine light and an active error P1171 is grounds for refusal to pass inspection. In addition, if this error is present, the content of harmful substances in the exhaust gases will exceed permissible standards due to incomplete combustion of fuel.
How much does it cost to repair error code P1171?
The cost of repairs varies from 1,000 rubles (diagnosis and reset if the error is false) to 30,000 rubles or more (replacement of injectors, catalyst or sensors). The average cost of replacing a mass air flow sensor with work is about 5,000-8,000 rubles, depending on the car model and region.