Trouble P0138 on Nissan: Oxygen Sensor High (Bank 1 Sensor 2) - Complete Guide

Error P0138 on cars Nissan - one of the most common problems associated with the exhaust and fuel supply system. This code points to overvoltage in the circuit of the second oxygen sensor (lambda probe) in the first bank of cylinders. Unlike errors P0130-P0135, which indicate a low signal or slow response, P0138 is directly related to too high voltage (usually above 1.2 V), which may indicate either a malfunction of the sensor itself or problems with the fuel mixture or electrical circuit.

Owners Nissan Qashqai, X-Trail, Almera and other models often encounter this error after refueling with low-quality fuel, long-term operation without replacing sensors, or after repairing the exhaust system. In this article we will look at:

• 🔍 What exactly does it mean Code P0138 and how it affects engine performance.
• 🛠️ Step-by-step diagnostics - from sensor testing to fuel system analysis.
• 💰 Repair cost in service vs. self-removal.
• ⚠️ Why is it dangerous? ignoring the error and how it affects fuel consumption.

What does error P0138 mean on Nissan: code decoding

Code P0138 stands for "O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)" - that is Oxygen sensor circuit is producing too high voltage. In the system Nissan Oxygen sensors are divided into:

• 🔹 Bank 1 - the side of the engine where it is located first cylinder (usually on the left when looking in the direction of travel).
• 🔹 Sensor 2 — lower lambda probe, located after the catalyst (unlike the top one, which stands before it).

The normal voltage of a working sensor fluctuates in the range 0.1–0.9 V. If the ECU records the value above 1.2 V longer than 2–3 seconds, an error is recorded P0138. The reasons may be different:

It is important to understand that P0138 does not always mean a sensor failure. For example, if there is a leak in the fuel system (a leaking injector or pressure regulator), the mixture becomes too rich and the sensor registers this as high voltage. Therefore, diagnosis must begin with checking sensor status And wiring integrity.

Symptoms of error P0138: how it manifests itself on Nissan

Error P0138 can remain undetected for a long time if it does not light up Check Engine. However, ignoring it is dangerous - over time it leads to:

• ⚠️ Increased fuel consumption (by 10–15%) due to incorrect mixture correction.
• 🔥 Catalyst overheatingif the mixture is too rich.
• 🚗 Dips during acceleration or unstable operation at idle.

The main signs that should alert you:

• 🔴 Check Engine light on (sometimes flashes when you press the gas sharply).
• 💨 The smell of gasoline from the exhaust pipe (indicates a rich mixture).
• 📉 Power drop, especially at rpm above 3000.
• 🔊 Popping sounds in the exhaust system when releasing gas.

⚠️ Attention: If the error P0138 accompanied by code P0420 (catalyst inefficiency), this may indicate destruction of the catalyst honeycomb due to prolonged operation with a rich mixture. In this case, urgent diagnosis is required!

On some models Nissan (For example, Qashqai J10/J11 or X-Trail T31/T32) the error may appear periodically - for example, during a cold start or after refueling. This is often associated with sensor contamination combustion products or bad contact in the connector.

How to diagnose error P0138 on Nissan: step-by-step instructions

For an accurate diagnosis you will need:

• 🔧 OBD-II scanner (For example, ELM327 or Launch CReader).
• 🔍 Multimeter to check voltage and resistance.
• 🛠️ Screwdriver and jack (if you need to remove the sensor).

Verification algorithm:

1. Count errors by scanner.

   Connect the scanner to the connector OBD-II (usually located under the steering wheel) and check:

   • 📊 Is there, in addition to P0138 other errors (eg P0172 - rich mixture).
   • 📈 Real-time oxygen sensor readings (should range from 0.1 to 0.9 V).
2. Visual inspection of the sensor and wiring.

   Find the second lambda probe (after the catalyst) and check:

   • 🔌 Connector integrity (is there any oxidation or broken contacts).
   • 🔥 Wire condition (whether it is rubbed against the exhaust pipe).
   • 💧 Presence of oil or coolant on the sensor (indicates leaks in the engine).

1. Заведите двигатель и прогрейте до рабочей температуры.
2. Подключите мультиметр в режиме DC к сигнальному проводу датчика (обычно чёрный или серый).
3. Напряжение должно колебаться в диапазоне 0.1–0.9 В. Если оно стабильно выше 1.2 В — датчик неисправен.

Checked with a scanner for other errors|

Inspected connector and wiring for damage|

Voltage measured with a multimeter|

Attempting to clean the sensor (if it is dirty) -->

If the sensor produces too much voltage, but visually appears to be working properly, the problem may lie in:

• 🔋 Short circuit signal wire on +12V.
• 🔥 Sensor overheating due to a faulty catalyst.
• ⚡ Weight problems (check the contact on the body).

How to fix error P0138: from simple to complex

Repair methods depend on the cause of the error. Let's start with the simplest and cheapest methods:

1. Cleaning the oxygen sensor

If the sensor is contaminated with combustion products (soot, oil), you can try cleaning it. To do this:

1. Remove the sensor with a key 22 mm (after disconnecting the connector).
2. Soak it for 30 minutes in phosphoric acid or a special cleaner (for example, Liqui Moly Lambda-Sensor-Reiniger).
3. Rinse with water and dry.

⚠️ Attention: Do not use sandpaper or metal brushes - this will damage the protective layer of the sensor!

2. Checking and repairing wiring

If the problem is in the wiring:

• 🔧 Call Use a multimeter to check the signal wire for a short circuit.
• 🔌 Strip and crimp contacts in the connector (oxidation often leads to false signals).
• 🔄 Check the circuit for open circuit - the resistance should be close to 0 ohm.

3. Replacing the oxygen sensor

If the sensor is faulty, it must be replaced. For Nissan original sensors fit:

• 🔹 Nissan 22690-4M200 (for Qashqai, X-Trail).
• 🔹 Nissan 22690-AL50A (for Almera N16, Primera P12).
• 🔹 Analogues: Bosch 0 258 006 537, Denso 234-4207.

The cost of the original sensor is from 3,000 to 6,000 rubles, analogue - from 1,500 to 3,000 rubles.

4. Fuel system diagnostics

If the error remains after replacing the sensor, check:

• 🔥 Injectors for overflow (you can check the cylinder balance).
• 🛢️ Fuel pressure (norm for Nissan — 3–4 bar).
• 🔧 Mass air flow sensor (mass air flow sensor) - its malfunction leads to incorrect preparation of the mixture.

Common mistakes when repairing P0138 on Nissan

Many car owners make mistakes that lead to the recurrence of P0138. That's what can't do:

• ❌ Ignore other errors. For example, if together with P0138 There is P0172 (rich mixture), replacing the sensor will not help - you need to look for the cause of the over-richness.
• ❌ Install non-original sensors of dubious quality. Cheap analogues often produce incorrect signals.
• ❌ Don't check the wiring. Even a new sensor will not work correctly if the signal wire is shorted to positive.
• ❌ Reset the error without eliminating the cause. If you just erase P0138 scanner, it will return in 10–20 km.

⚠️ Attention: On some Nissan (For example, Pathfinder R51 or Navara D40) error P0138 may appear after chip tuning. This is due to altered fuel maps causing the mixture to become too rich. In this case, the firmware needs to be adjusted!

Cost of repairs in service vs. do-it-yourself repair

Elimination prices P0138 vary depending on the cause:

Do-it-yourself repairs are more profitable, but require time and tools. If you are not confident in your abilities, it is better to contact the service - especially if the error is accompanied by other problems (for example, P0300 — misfires).

FAQ: Frequently asked questions about error code P0138 on Nissan