Error P0420 on Nissan: low catalyst efficiency - what to do?

Fault code P0420 - one of the most common problems among owners Nissan with a mileage of 100,000 km. It signals a decrease in the efficiency of the catalytic converter, but in practice there can be many more reasons. If the dashboard lights up Check Engine, and the scanner showed exactly this code, do not rush to immediately change the expensive catalyst. In 40% of cases, the problem lies in the oxygen sensors, fuel system, or even the ECU firmware.

In this article we will look at all possible causes of P0420 on models Nissan Qashqai, X-Trail, Teana, Almera and others, we’ll tell you how to correctly diagnose a malfunction without extra expenses, and give step-by-step instructions for troubleshooting. We will pay special attention method for checking the catalyst without removing - this will save you time and money.

What does the P0420 code mean on Nissan?

Code P0420 stands for "Catalyst System Efficiency Below Threshold (Bank 1)" — catalyst efficiency is below the threshold value in the first row of cylinders. The ECU records this error when data from the lower (second) oxygen sensor HO2S indicate insufficient purification of exhaust gases.

It is important to understand that P0420 does not always mean a bad catalytic converter. This is a general code that may indicate:

• 🔧 Wear or destruction of the catalytic converter (especially on cars older than 10 years)
• 📊 Malfunction of oxygen sensors (lambda probes) - upper or lower
• ⛽ Problems with the fuel system: rich/lean mixture, faulty injectors
• 🔥 Misfires leading to catalyst overheating
• 💻 Errors in ECU firmware (relevant for Nissan Juke And Note with engines HR16DE)

On Nissan with engines QR25DE, MR20DE And VQ35DE error P0420 often appears after 150,000 km. On diesel models (Navara, Pathfinder) it may be related to the particulate filter DPF.

The main causes of P0420

In order not to waste money on replacing the catalyst in vain, you need to consistently check all possible causes. Let's start with the most common ones:

1. Malfunction of the catalytic converter

Over time, the catalyst honeycomb becomes clogged or destroyed. On Nissan this often happens due to:

• 🛢️ Using low-quality gasoline with high sulfur content
• 🔥 Overheating of the catalyst due to misfires
• 🚗 Mechanical damage (impacts to the exhaust system)

Signs of a "dying" catalyst: loss of power at high speeds, popping sounds in the exhaust system, hydrogen sulfide smell ("rotten eggs").

2. Problems with oxygen sensors

Sensors HO2S (or lambda probes) measure the oxygen content in the exhaust. If they give incorrect readings, the ECU mistakenly records low catalyst efficiency. On Nissan fail more often:

• 🔴 Upper sensor (before the catalyst) - responsible for correcting the fuel mixture
• 🟢 Lower sensor (after the catalyst) - monitors cleaning efficiency

Symptoms of sensor failure: floating speed idling increased fuel consumption, Check Engine light on with codes P0130-P0167.

How to check oxygen sensors with a multimeter?

To check the top sensor:

1. Start the engine and warm up to operating temperature.

2. Connect a multimeter in voltmeter mode to the signal wire of the sensor (usually black or gray).

3. At idle speed, the voltage should fluctuate from 0.1 to 0.9 V with a frequency of 2-3 times per second.

If the readings are stable or outside the limits, the sensor is faulty.

3. Problems with the fuel system

A rich or lean fuel mixture will cause the catalytic converter to malfunction. On Nissan this may be caused by:

• 🛢️ Dirty or faulty injectors
• 🔧 Faulty fuel pressure regulator
• 💨 Air leaks through cracks in the intake manifold
• 🔥 Dirty air filter

Indirect signs of problems with the fuel system: black smoke from the exhaust pipe (rich mixture) popping sound in the muffler (lean mixture) loss of dynamics during acceleration.

4. Misfire

Unburned fuel enters the catalyst and burns out there, causing it to overheat and destroy. On Nissan Misfires are often associated with:

• 🔌 Faulty spark plugs or coils
• 🛢️ Worn out high-voltage wires
• 🔧 Incorrect operation of the ignition system (especially on engines VQ35DE)

If together with P0420 there are codes P0300-P0306 (misfires), fix them first - this may solve the problem with the catalytic converter.

5. ECU firmware

On some models Nissan (especially Juke, Note, Almera with engines HR16DE) error P0420 may appear due to a “crooked” ECU firmware. This is due to incorrect threshold values ​​for the oxygen sensors.

Signs of a software error: Check Engine Lights Intermittently, no other symptoms of malfunction, after resetting the error it returns after 100-200 km.

How to Diagnose P0420 on a Nissan: Step-by-Step Instructions

Before going to the service center, you can conduct preliminary diagnostics yourself. Here is the algorithm of actions:

Step 1: Count all errors

Use a diagnostic scanner (eg ELM327 or Launch CReader) or contact the service for a complete error reading. Please note the accompanying codes:

• 🔴 P0130-P0167 - problems with oxygen sensors
• 🔥 P0300-P0306 - misfires
• ⛽ P0171/P0172 - lean/rich mixture

Step 2: Visual Inspection

Carry out an external inspection:

• 👀 Check the integrity of the exhaust system (cracks, dents)
• 🔧 Inspect the oxygen sensor wires for damage
• 🛢️ Check the condition of the spark plugs (carbon deposits, gaps)

Step 3: Check Oxygen Sensors

To do this you will need a multimeter or oscilloscope. Verification algorithm:

1. Warm up the engine to operating temperature.
2. Connect to the signal wire of the upper sensor (usually a 4-wire connector: 2 power, 1 signal, 1 ground).
3. At idle speed the voltage should fluctuate in the range 0.1-0.9 V.
4. Press the gas sharply to 3000 rpm - the voltage should drop to 0.1-0.2 V, then return to oscillation.

If the readings are stable or outside the limits, the sensor is faulty. Check the lower sensor (after the catalyst) in the same way. His readings should be more stable: 0.4-0.6 V with slight fluctuations.

Step 4: Checking the catalyst without removing it

There are two reliable ways to check the catalyst without removing it:

Method 1: Back Pressure Test

1. Remove the upper oxygen sensor (before the catalyst).
2. Install the pressure gauge into the sensor hole.
3. Start the engine and increase the speed to 3000 rpm.
4. Normal back pressure: up to 0.35 kg/cm². If it is higher, the catalyst is clogged.

Method 2: Temperature test

1. Use a pyrometer to measure the exhaust pipe temperature before and after the catalyst.
2. With a working catalyst, the temperature after it should be at 10-30% higherthan before.
3. If there is no difference, the catalyst does not work.

Step 5: Check the fuel system

If the catalyst and sensors are ok, check:

• 🛢️ Fuel rail pressure (standard: 3.0-3.5 bar for the majority Nissan)
• 🔧 The condition of the injectors (can be checked on a stand or washed with ultrasound)
• 💨 Intake manifold sealing (use a smoke generator or WD-40)

On engines QR25DE And VQ35DE Often air leaks occur through cracks in the manifold or the gasket of the intake pipe.

Table: Common Causes of P0420 on Popular Nissan Models

Model Nissan	Engine	Common causes of P0420	Recommendations
Qashqai J10/J11	MR20DE, HR16DE	Catalyst wear, malfunction of the lower oxygen sensor, air leaks	Check the sensors, inspect the intake manifold for cracks
X-Trail T31/T32	QR25DE, MR20DD	Clogged catalyst, misfires (plugs, coils), rich mixture	Diagnose the ignition system, check fuel pressure
Teana J32	VQ35DE, QR25DE	Malfunction of the upper oxygen sensor, ECU firmware, catalyst wear	Update the firmware, check the sensors with an oscilloscope
Almera N16/G15	HR16DE, K4M	False alarm due to firmware, faulty ignition coils	Check for firmware updates, diagnose ignition
Navara D40	YD25DDTi	Problems with the particulate filter DPF, malfunction of the exhaust gas temperature sensor	Regenerate DPF, check the sensors

How to resolve error P0420: from simple to complex

Depending on the cause, solutions to P0420 can range from a simple sensor replacement to a complex repair. Let's consider solutions by degree of complexity.

1. Replacing oxygen sensors

If the diagnostics showed a malfunction of the sensors, they need to be replaced. On Nissan often fail:

• 🔴 Upper sensor (article: 22690-4M015 for QR25DE)
• 🟢 Lower sensor (article: 22690-AL60A for VQ35DE)

Replacement Tips: Use original sensors or high-quality analogues (For example, Denso or NGK). Apply thermal paste to the threads before installation - this will make future replacement easier. After replacement, reset errors and drive 50-100 km to adapt the ECU.

2. Cleaning or replacing the catalyst

If the catalyst is clogged but not destroyed, you can try cleaning it. Methods:

• 🧹 Mechanical cleaning: remove the catalyst, wash it with Karcher and special means (for example, Liqui Moly Pro-Line)
• 🔥 Dry cleaning: use catalyst cleaning additives (e.g. Hi-Gear HG3270)

If the catalyst is destroyed (a ringing sound is heard inside the can), it needs to be replaced. Alternatives:

• 🆕 Original catalyst (expensive but reliable)
• 🔧 Universal catalyst (cheaper, but requires welding)
• ⚠️ Replacing or removing the catalyst (illegal in most countries, requires ECU flashing)

3. Fuel system repair

If the problem is in the fuel mixture:

• 🛢️ Clean the injectors (ultrasound or liquid method)
• 🔧 Replace the fuel filter (on Nissan recommended every 60,000 km)
• 📊 Check the fuel pressure regulator (on engines MR20DE it leaks often)

On Nissan Teana And Maxima with engines VQ35DE A common problem is clogged injectors. Cleaning them often solves the P0420 problem.

4. Elimination of misfires

If there are pass codes (P0300-P0306):

• 🔌 Replace spark plugs (on Nissan original spark plugs last 60-80,000 km)
• 🔥 Check the ignition coils (especially on engines HR16DE And MR20DE)
• 🛢️ Measure compression (norm: 12-14 bar, spread between cylinders no more than 1 bar)

5. ECU firmware update

If error P0420 appears intermittently without other symptoms, check that the firmware is up to date. On Nissan Juke And Note with engines HR16DE There are official updates that eliminate false positives.

The firmware update can only be done at the official service center or from chip tuning specialists. Cost: from 3,000 to 8,000 rubles.

Cost of repairs: what is cheaper - repair or sell?

Repair prices vary depending on the cause of P0420 and the model. Nissan. Here are the approximate prices for Moscow and the regions (2026):

Type of repair	Cost (RUB)	Working period	Warranty
Diagnostics (full)	1 500 — 3 000	1-2 hours	—
Replacing the upstream oxygen sensor	2,500 – 5,000 (with work)	30-60 min	6-12 months
Replacing the downstream oxygen sensor	3,000 – 6,000 (with work)	1 hour	6-12 months
Cleaning the catalyst (removal/installation)	4 000 — 8 000	2-3 hours	3-6 months
Replacing the catalyst (original)	25 000 — 60 000	3-5 hours	12-24 months
Replacing the catalyst (universal)	12 000 — 25 000	4-6 hours	12 months
Cleaning injectors (ultrasound)	3 000 — 6 000	2 hours	6 months
ECU firmware update	3 000 — 8 000	1 hour	—

If your Nissan older than 10 years and has a mileage of 200,000 km, replacing the catalyst may not be cost-effective. In this case, owners often choose:

• 🔧 Installation flame arrester + sensor blende (cost: 8,000 - 15,000 rubles)
• 💰 Selling the car “as is” (indicating the problem in the ad)

Common mistakes when repairing P0420

Many owners Nissan They are wasting money trying to resolve P0420 using the wrong methods. Here are the most common mistakes:

⚠️ Attention! Do not reset the P0420 code without correcting the cause. ECU Nissan remembers the history of faults, and the next time you scan you will see Pending Code (pending code) even if Check Engine does not burn.

Error 1: Replacing the catalyst without checking the sensors

Up to 30% of owners Nissan They change the catalyst, although the problem was a faulty lower oxygen sensor. Always check the sensors to replacing the catalyst!

Mistake 2: Using cheap oxygen sensors

Non-original sensors (especially Chinese ones) often give incorrect readings, which leads to the reappearance of P0420. On Nissan It is recommended to use sensors Denso or NGK.

Error 3: Ignoring misfires

If misfires are not corrected, the new catalyst will quickly fail. Always check the plugs, coils and compression when diagnosing P0420.

Error 4: Removing the catalyst without flashing the ECU

Simply cutting out the catalyst and installing the blende is not enough. On most Nissan after 2010 this will lead to constant burning Check Engine and switching to emergency mode.

⚠️ Attention! On Nissan with engines VQ35DE And QR25DE after replacing the catalyst or oxygen sensors, it is necessary to reset the fuel system adaptations via a diagnostic scanner (for example, Launch X431 or Bosch KTS). Without this, the ECU will use the old adjustments and the error may return.

FAQ: Answers to frequently asked questions about P0420 on Nissan

Is it possible to drive with P0420?

Short term - yes, but not recommended for long term. Driving for a long time with a faulty catalyst or a rich mixture can lead to:

• 🔥 Overheating and destruction of the catalyst (fragments can get into the cylinders)
• 🛢️ Increased fuel consumption (up to 20-30%)
• 🚗 Loss of power and unstable engine operation

If the error appeared recently and there are no other symptoms, you can go to the service center. If there is popping sounds in the exhaust system or hydrogen sulfide smell - It’s better to call a tow truck.

I reset the P0420 error, but it returned after 100 km. What to do?

This is a typical situation when the problem persists. Probable reasons:

• 🔧 Malfunction downstream oxygen sensor (most common reason)
• 🛢️ Air leak in the intake manifold
• 💻 Incorrect adaptations of the fuel system (reset via scanner required)

Recommendation: spend full diagnostics with checking the sensors with an oscilloscope and testing the tightness of the intake system.

How realistic is it to clean the catalyst yourself?

Cleaning the catalyst without removal (with additives) gives a temporary effect (for 10-30,000 km). A more reliable method is mechanical cleaning with removal:

1. Remove the catalyst (on most Nissan this requires a grinder or welding).
2. Wash it with Karcher and a special cleaner (for example, Liqui Moly Pro