Modern car Nissan Qashqai is equipped with a sophisticated engine management system that constantly monitors the composition of exhaust gases. When the icon lights up on the dashboard Check Engine, and the scanner issues a code P0138, this is a signal of a serious malfunction in the second lambda probe circuit. This problem is typical not only for crossovers, but also for many other models of the concern, however Nissan Qashqai with 1.6 or 2.0 engines it occurs quite often due to the design features of the exhaust system.
Ignoring this error can lead to incorrect operation of the catalyst, increased fuel consumption and, ultimately, expensive engine repairs. Code P0138 indicates that the signal voltage from the Bank 1 Sensor 2 oxygen sensor exceeds the permissible limit (usually above 1.2 Volts) for a specified time. This means that the engine management system sees a "rich" mixture, even though in fact the air-fuel mixture may be normal.
The essence of the fault code and the principle of operation of the sensor
To understand the nature of the breakdown, it is necessary to understand how the system functions. The second lambda probe (Sensor 2) is installed after the catalyst and serves to monitor its efficiency. Unlike the first sensor, which is involved in adjusting the fuel supply, the second sensor only transmits information about how well the catalyst cleans exhaust gases. If the voltage at its output is constantly high, the ECU concludes that the catalyst is not working or that too much fuel is entering the mixture.
Code P0138 stands for "Oxygen Sensor Circuit (Bank 1, Sensor 2) High Input." This means that the voltage potential on the signal wire exceeds the standard values. In normal mode, after the catalyst, the voltage should be stable and low (about 0.45 V), since the catalyst should reduce the oxygen content. High voltage simulates the state of a “lean” mixture, but in the context of this code we are talking specifically about exceeding the voltage threshold, which is interpreted by the system as an anomaly.
Feature Nissan Qashqai lies in the sensitivity of the ECU to changes in resistance in the circuit. Even minor power surges can be reported as an error if they last longer than a certain amount of time. It is important to understand that the code itself P0138 does not always mean failure of the sensor itself. The problem may lie in the wiring, a short circuit to the positive wire, or incorrect operation of the fuel system.
The main causes of error P0138
The range of reasons that trigger this code is quite wide and ranges from trivial wiring problems to serious engine malfunctions. The most common cause is physical damage or wear to the lambda probe itself. Over time, the sensor's heating element can fail and the sensing part can become contaminated with lead or silicone, resulting in high voltage readings.
An equally common problem is with the electrical circuit. In the Russian climate, with its temperature changes and reagents, the insulation of the exhaust system wires often dries out and cracks. This can cause the signal wire to short to power (positive) or to ground, which the ECU interprets as a high voltage signal. It is also worth checking the integrity of the connector, since oxidation of the contacts can create false resistance.
- 💥 Short circuit signal wire of the sensor to the 12 Volt power supply circuit.
- ⚡ Malfunction heating element lambda probe, leading to overheating and signal distortion.
- 🔧 Problems with fuel system: The mixture is too rich due to overfilling of the injectors or a faulty pressure regulator.
- 🔥 Depressurization exhaust manifold or burnout of the gasket, due to which air leaks distort the readings.
Sometimes the reason lies not in the exhaust system, but in the operation of the engine. If the injectors are leaking or the mass air flow sensor (MAF) is transmitting incorrect data, the mixture becomes too rich. In this case, even a working sensor after the catalyst will show a high voltage, since it will record the actual excess amount of fuel in the exhaust.
Symptoms and effects on vehicle performance
When an error occurs P0138 The driver may notice a number of characteristic signs indicating problems with the engine. The most obvious symptom is a lit lamp. Check Engine on the dashboard. In some cases, the system may go into limp mode, limiting engine speed or reducing power to prevent further damage to components.
The vehicle's behavior may become unstable. You may notice jerks when accelerating, floating idle speeds, or even a stalling engine when stopping. Fuel consumption often increases because the ECU, receiving incorrect data about the composition of the mixture, tries to adjust the fuel supply, making it too rich. This is especially noticeable when driving on the highway or in the city cycle.
⚠️ Attention: Operation Nissan Qashqai with a faulty catalyst and high voltage on the oxygen sensor can lead to its complete destruction. Ceramic fragments from a collapsed catalyst can enter the engine cylinders, causing catastrophic damage to the piston group.
In addition, the malfunction may manifest itself as the smell of unburnt fuel from the exhaust pipe. If the mixture is too rich, it does not have time to burn in the cylinders and is burned out in the catalyst or simply thrown out. This not only harms the environment, but can also lead to overheating of the exhaust system.
Diagnostics and testing of the sensor circuit
Before you run to the store for a new sensor, you need to conduct a thorough diagnosis. The first step is to visually inspect the wiring going to the oxygen sensor. Check for signs of melting, insulation chafing or oxidation of the contacts in the connector. Often the problem is solved by simply cleaning the contacts or restoring the insulation.
For accurate diagnosis you will need a multimeter. It is necessary to measure the resistance of the sensor heating element. To do this, disconnect the sensor connector and measure the resistance between the heater contacts (usually two thick wires). The value must be within specification, usually between 2 and 10 ohms, depending on the sensor model. If the resistance is infinite or zero, the sensor must be replaced.
☑️ Lambda probe diagnostics
The next stage is checking the signal. Connect the multimeter to the signal wire and ground. When the engine is running, the voltage should fluctuate smoothly (although for the sensor after the catalyst it is more stable). If the voltage is consistently recorded above 1.2 Volts, this confirms a high signal error. Also check for supply voltage at the sensor connector.
How to check a sensor with an oscilloscope?
An oscilloscope allows you to see the dynamics of signal changes over time. If the signal is a straight line at a high level, this is a clear sign of a shorted or faulty sensor. Normally, after the catalyst, the signal should be relatively smooth, but with small deviations, and not fixed at the maximum.
It is also important to check the operation of the fuel system. If you suspect that the mixture is really rich, it is worth checking the injectors for leaks and the operation of the fuel pressure regulator. Error P0138 may be a consequence not of the sensor, but of a real problem with the fuel supply.
Procedure for replacing and adjusting the sensor
If diagnostics confirm that the sensor is faulty, it must be replaced. For Nissan Qashqai It is recommended to use original spare parts or high-quality analogues, such as NTK or Bosch. Installing a low-quality sensor may cause the error to reappear within a short time. Before starting work, be sure to let the engine cool down, as the exhaust system gets very hot.
The replacement process involves disconnecting the negative terminal of the battery, disconnecting the sensor connector and unscrewing the element itself using a special key for the lambda probe. Be careful not to damage the threads. When installing a new sensor, apply a special non-stick lubricant to the threads, if it is not pre-applied by the manufacturer.
| Parameter | Normal value | Meaning for error P0138 | Permissible deviation |
|---|---|---|---|
| Signal voltage (Sensor 2) | 0.4 - 0.6 V | > 1.2 V | ± 0.1 V |
| Heater resistance | 2 - 10 Ohm | ∞ (break) or 0 (short circuit) | ± 1 ohm |
| Reaction time | < 100 ms | > 500 ms | - |
| Exhaust temperature | 400 - 800 °C | Unstable | - |
After installing a new sensor, you need to reset the errors using the diagnostic scanner. Simply disconnecting the battery is not enough, since adaptation values may be stored in the ECU memory. Start the engine and let it idle for a few minutes until the system reaches operating temperature and begins to adjust parameters.
When purchasing a new sensor, pay attention to the wire length and connector configuration. Sometimes the wires are too short and you will have to extend them, which is not desirable for signal reliability.
If the error does not disappear after replacement, the problem most likely lies in the wiring or the engine control unit itself. In rare cases, it may be necessary to reflash the ECU or replace the unit itself, but this happens extremely rarely.
- Do it yourself with a multimeter
- Contacting service
- Search by symptoms
- Using an OBD2 scanner
⚠️ Attention: Do not use sealant or thread locker on the oxygen sensor unless necessary. Chemicals can contact the sensing element and damage it, causing false readings and errors. P0138.
Prevention and operating features
To avoid the reoccurrence of the error, it is recommended to carry out regular vehicle maintenance. Monitor the condition of the fuel system and use high-quality fuel. Impurities in gasoline can quickly poison the catalyst and lambda probes, leading to their failure.
It is also worth paying attention to the operation of the engine. Any signs of unstable operation, such as tripping or misfires, can lead to overheating of the catalyst and damage to the sensors. Timely replacement of spark plugs and coils will help avoid such problems.
Regular diagnostics of the exhaust system and the use of high-quality fuel are the key to a long life of lambda probes and catalyst on Nissan Qashqai.
In winter, when roads are treated with reagents, check the condition of the wiring under the bottom of the car. Salt and moisture accelerate corrosion of contacts, which can lead to a short and a code. P0138. If you notice traces of corrosion on the connectors, immediately treat them with a special product.
Frequently asked questions from Nissan Qashqai owners
Is it possible to drive with P0138?
Technically it is possible to drive, but it is not recommended for long periods of time. This can lead to catalytic converter failure and increased fuel consumption. If the error appeared recently, you can go to the service center, but it is better to eliminate the cause as soon as possible.
Does resetting the error by disconnecting the battery help?
There may be a temporary effect, but if the cause of the malfunction is not eliminated (for example, a short circuit or a faulty sensor), the error will return after several engine cycles. Resetting only clears the memory, but does not fix the problem.
Is it possible to replace the sensor with a universal one?
Yes, universal sensors exist, but they are more difficult to connect correctly. You need to know the pinout and connect the wires correctly. For Nissan Qashqai It is better to use the original connector or a special adapter to avoid signal problems.
Does the quality of gasoline affect the occurrence of an error?
Yes, low-quality fuel with a high content of additives can quickly poison the sensitive element of the lambda probe and the catalyst. This is one of the most common causes of errors in oxygen sensors.
How much does it cost to replace a sensor at a service center?
The cost of work depends on the region and service. Typically the price includes replacement labor and diagnostics. The sensor itself can cost from 3,000 to 10,000 rubles, depending on the brand and model, and work can cost from 1,500 to 3,000 rubles.
Solving a code problem P0138 requires a systematic approach. Do not rush to change parts at random, but conduct a thorough diagnosis of the wiring and the fuel system itself. Proper repair will ensure the stable operation of your Nissan Qashqai and will prevent more serious damage in the future.