Error P0138 on the dashboard Nissan - a signal about problems with the oxygen sensor (lambda probe), which is responsible for the correct operation of the fuel system. This code points to excess voltage in the oxygen sensor heater circuit (Bank 1, Sensor 2), which can lead to increased fuel consumption, unstable engine operation, or even failure of the catalytic converter. Owners Qashqai, X-Trail, Juke and other models Nissan people often encounter this error, but do not always understand how to correctly diagnose and fix it.

In this article we will look in detail at what it means P0138, what symptoms accompany it, and provide step-by-step repair instructions - from a simple wiring check to replacing the sensor. You will also find out whether it is possible to drive with this error and what the consequences of ignoring the problem are. If you are not an auto electrical specialist, don’t worry: we will explain everything in simple language, with photos, diagrams and practical tips.

What does P0138 mean on Nissan?

Code P0138 stands for "Circuit High Voltage Bank 1 Sensor 2" — increased voltage in the heater circuit of the second oxygen sensor (lower lambda probe), located after the catalyst. This sensor monitors the efficiency of the catalytic converter and transmits data to the ECU (electronic control unit) to adjust the air-fuel mixture.

Unlike the upper sensor (Sensor 1), which regulates the mixture composition in real time, the lower one (Sensor 2) serves to monitor the exhaust gases after the catalyst. If the voltage in its heating circuit exceeds the permissible 0.45–0.55 V, The ECU records an error P0138 and includes Check Engine.

  • 🔧 Bank 1 - the side of the engine where the first cylinder is located (usually on the left, when viewed in the direction of travel).
  • ⚡ Sensor 2 - second oxygen sensor installed after catalyst.
  • 📉 Heater — built-in heating element that quickly brings the sensor to operating temperature (300–400°C).

The error can be either temporary (due to poor contact) or permanent (due to a faulty sensor or wiring). In some cases P0138 appears along with other codes, e.g. P0130 (sensor circuit malfunction) or P0141 (Sensor 2 heater malfunction).

📊 How long has your Check Engine light been on with error P0138?
  • Less than a week
  • 1–2 weeks
  • More than a month
  • Constantly flashing
  • I don't know

The main causes of error P0138

Causes of occurrence P0138 There are several, and they are divided into two groups: problems with the sensor itself and faults in the electrical circuit. Let's look at them in detail.

1. Malfunction of the oxygen sensor (lambda probe)

The most common reason is the failure of the second oxygen sensor. Over time, its sensitive element becomes covered with soot, and the heater stops working correctly. Symptoms:

  • 🔥 The sensor does not heat up to operating temperature.
  • 📉 Voltage readings are too high or chaotic.
  • ⚡ Short circuit in the heater circuit.

2. Problems with wiring or connector

Damaged wire insulation, oxidized contacts or an open circuit can lead to false signals. Often the problem lies in:

  • 🔌 Sensor connector (moisture ingress, corrosion).
  • 🔧 Wires going from the sensor to the ECU (frayed, fractured).
  • 🛠️ Heater circuit fuse (rare, but it happens).

3. Problems with the ECU or firmware

In rare cases, an error P0138 occurs due to a malfunction in the control unit software. This is relevant for Nissan Qashqai J10/J11, X-Trail T31/T32 and other models with electronic injection systems. Signs:

  • 🖥️ The error appears after flashing the ECU.
  • 🔄 The code disappears after resetting, but returns after a few km.
Reason Probability Verification method
Oxygen sensor malfunction 70% Checking the heater resistance, oscilloscope
Wiring damage 20% Visual inspection, testing with a multimeter
Oxidation of connector contacts 5% Cleaning contacts, checking voltage
ECU or firmware failure 5% Diagnostics with a scanner, error reset
⚠️ Attention: If the error P0138 appeared after replacing the sensor, check its compatibility with your model Nissan. Cheap analogues often give false signals due to a mismatch in the heater resistance.

Symptoms of error P0138: how does it manifest itself?

Error P0138 is not always accompanied by obvious signs of malfunction, but there are several symptoms worth paying attention to:

  • 🚨 Check Engine light on — the main indicator. On some Nissan (For example, Juke) error may flash.
  • ⛽ Increased fuel consumption — The ECU goes into emergency mode, enriching the mixture.
  • 🔊 Rough engine operation - especially at idle or during acceleration.
  • 💨 Sulfur smell from exhaust pipe - a sign of an over-enriched mixture or a faulty catalyst.

On some models (for example, Nissan Qashqai 2.0) the error may only appear during a cold start or after a long trip. In this case, the problem is often associated with the sensor heater, which does not have time to heat up.

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If after resetting the error P0138 it returns after 10–20 km, most likely the sensor itself is to blame. If the code appears immediately, check the wiring or ECU.

How to diagnose trouble code P0138 on Nissan?

Diagnostics P0138 requires a systematic approach. Start with the simplest checks and gradually move on to more complex ones. You will need:

  • 🔧 Multimeter (to check voltage and resistance).
  • 🔍 Diagnostic scanner (for example, ELM327 or Launch CReader).
  • 🛠️ Oscilloscope (optional, for in-depth diagnostics).

Step 1: Read errors with the scanner

Connect the diagnostic tool to the connector OBD-II (usually located under the steering wheel) and read the codes. Please note:

  • If except P0138 There is P0130–P0141, the problem is definitely in the sensor or wiring.
  • If there is only one error, check the heater circuit.

Step 2: Checking the Oxygen Sensor

To check the second sensor (Sensor 2):

  1. Disconnect the sensor connector.
  2. Measure the heater resistance: normal - 2–10 ohms (depending on the model).
  3. Check the voltage at the connector with the ignition on: there should be 12 V.

Disconnect the sensor connector|Measure the heater resistance|Check the voltage at the connector|Inspect the wires for damage-->

Step 3: Check Wiring

Inspect the wires coming from the sensor to the ECU:

  • 🔍 Look for rubbing, melting or traces of corrosion.
  • 🔌 Check the connector contacts for oxidation.
  • 📊 Check the circuit with a multimeter for an open or short circuit.
⚠️ Attention: On Nissan X-Trail T32 And Qashqai J11 The oxygen sensor wires often rub against the exhaust manifold. Be sure to check their condition!

How to fix error P0138: step-by-step instructions

The repair method depends on the cause of the error. Below are step-by-step actions for each case.

1. Cleaning or replacing the oxygen sensor

If the sensor is dirty (for example, due to low-quality fuel), you can try to clean it:

  1. Remove the sensor with a key 22 mm (on some models - on 16 mm).
  2. Immerse it in phosphoric acid or a special cleaner for 10–15 minutes.
  3. Rinse with water and dry.

If cleaning does not help, replace the sensor. For Nissan original sensors fit NTK or Denso, as well as high-quality analogues (Bosch, NGK).

2. Wiring repair

If the problem is in the wires:

  • 🔧 Insulate damaged areas with heat shrink tube.
  • 🔌 Clean the connector contacts with alcohol or special liquid.
  • 🛠️ Replace broken chips (for example, with Nissan Juke The plastic clamp of the connector often breaks).

3. ECU check

If the error returns after replacing the sensor and checking the wiring:

  • 🖥️ Reset the ECU adaptations via the diagnostic scanner.
  • 🔄 Update the firmware (relevant for Nissan Qashqai 1.6 And X-Trail 2.5).
  • 🔧 Check the mass of the ECU (sometimes the contact on the body oxidizes).
How to reset ECU adaptations?

To reset adaptations, connect the scanner, select the function Reset ECU Adaptations or Clear Long-Term Fuel Trims. Error after reset P0138 may disappear if the problem was a temporary glitch.

Is it possible to drive with P0138?

Short driving with error P0138 possible, but not desirable. Here's what to expect:

  • ⛽ Increased fuel consumption on 10–15% (The ECU goes into emergency mode).
  • 🚗 Decreased dynamics - the car accelerates worse.
  • 💨 Risk of catalytic converter damage - due to the wrong mixture, it may melt.

If the error appears for the first time, you can go to a service station or garage, but you should not delay the repair. On Nissan with turbocharged engines (For example, Qashqai 1.6 DIG-T) ignoring P0138 can lead to serious damage to the turbine or injection system.

⚠️ Attention: On some models (for example, Nissan Pathfinder R51) long driving with an error P0138 leads to failure of the second oxygen sensor and the need to replace the catalyst (cost - from 30 000 ₽).

Preventing error P0138 on Nissan

To avoid reappearance P0138, follow these guidelines:

  • ⛽ Use high-quality fuel (octane number not lower than 95).
  • 🔧 Regularly check the condition of the oxygen sensor wiring (especially on Nissan with over 100,000 km mileage).
  • 🛠️ Change oxygen sensors every 80,000–100,000 km (or sooner if there are signs of trouble).
  • 🔥 Monitor the condition of the catalyst - its clogging can lead to false errors.

On Nissan with HR16DE engines And MR20DD It is recommended to install sensors with original connectors - this reduces the risk of contact oxidation. Also avoid driving through deep puddles: water can get into the sensor connector and cause a short circuit.

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Regular scanner diagnostics (every 3-6 months) help identify problems with oxygen sensors at an early stage and prevent costly repairs.

FAQ: Frequently asked questions about error P0138

Could P0138 be caused by bad gasoline?

Yes, low-quality fuel with high sulfur content or additives can contaminate the oxygen sensor, which will lead to an error. P0138. If, after refueling at an unfamiliar gas station, a Check Engine, try draining the fuel and refilling with proven gasoline. It is also recommended to add an injector cleaner (for example, Liqui Moly).

How much does it cost to replace an oxygen sensor on a Nissan?

The cost depends on the model and type of sensor:

  • Original sensor (For example, NTK 25050 for Qashqai) — 5 000–8 000 ₽.
  • Analogue (Bosch, Denso) — 2 500–4 000 ₽.
  • Replacement work — 1 000–2 000 ₽ (if the sensor is “stuck”, the price may increase).

On Nissan X-Trail And Murano with V6, replacing the lower sensor is more difficult due to its location, so the cost of work can reach 3 000 ₽.

Is it possible to simply reset the P0138 code without repairing it?

You can reset the error, but it will return if the problem is not resolved. On some Nissan (For example, Juke or Note) the error may disappear for a while, but this does not mean that the problem has disappeared. Prolonged ignoring P0138 will lead to:

  • Increased wear of the catalyst.
  • Deterioration of dynamics and increased fuel consumption.
  • Possible ECU failure due to incorrect signals.
How can you tell the difference between a sensor failure and a wiring problem?

The simplest way is to measure the resistance of the sensor heater:

  1. Disconnect the sensor connector.
  2. Connect a multimeter in ohmmeter mode to the heater contacts (usually white and black wires).
  3. If resistance 2–10 ohms - the sensor is working if 0 ohm (short circuit) or ∞ (break) - the sensor is faulty.

If the sensor is working, check the wiring for an open or short. Also inspect the connector for oxidation.

Can P0138 appear after replacing the exhaust system?

Yes, if when replacing:

  • Damaged oxygen sensor wiring.
  • A non-standard catalyst or flame arrester was installed (this changes the exhaust gas parameters).
  • The sensor connector was connected incorrectly (the contacts were mixed up).

In this case, check:

  • Integrity of wires.
  • The connector is connected correctly.
  • Compatibility of the new catalyst with the ECU.