Error P0420 on Nissan Qashqai: catalytic converter or sensor fault?

You saw on the dashboard Nissan Qashqai alarm indicator Check Engine, and the scanner issues a code P0420 — “Is the efficiency of the catalytic reduction system below the threshold”? This error is one of the most common on gasoline versions. Kashkaya (especially with motors HR16DE, MR20DE And M9R), but its reasons are not always obvious. In 80% of cases the problem is related to catalytic converter, but oxygen sensors and even ECU firmware may be to blame.

In this article we will look at all possible causes of P0420 on Nissan Qashqai (including models J10, J11 and restyled versions), we will explain how to correctly diagnose a malfunction, and give step-by-step instructions for troubleshooting - from simple cleaning of sensors to replacing the catalyst with blende. You will also learn why the error may appear after replacing the exhaust system or chip tuning, and what to do if the problem returns after a reset.

What does error P0420 mean on Nissan Qashqai

Code P0420 indicates that catalytic converter efficiency (catalyst) below the permissible threshold. In modern Nissan Qashqai is responsible for this rear oxygen sensor (lambda probe), which compares the level of harmful emissions before and after the catalyst. If the difference in readings is too small, the ECU records an error.

It is important to understand: P0420 does not always mean that the catalytic converter has died. Sometimes the problem lies in:

• 🔧 Faulty lambda probe (especially the rear, but sometimes the front).
• 🔥 Air leak in the exhaust system (cracks in the manifold, burnt gaskets).
• 💻 Incorrect ECU firmware (relevant after chip tuning).
• ⚡ Problems with the fuel system (rich/lean mixture due to injectors or mass air flow sensor).

On Qashqai with diesel engines (M9R, R9M) error P0420 occurs less frequently, but may indicate a clogged diesel particulate filter (DPF) or system malfunction EGR.

Causes of error P0420: from simple to complex

In order not to waste money on unnecessary spare parts, diagnostics should be carried out according to algorithm “from cheap to expensive”. Start by checking the sensors and the tightness of the system, and only then move on to the catalyst.

Reason	Symptoms	Repair cost (approx.)
Faulty lambda probe (rear)	The error appears when it is cold and disappears after a reset. Increased fuel consumption.	2,000–5,000 ₽ (sensor replacement)
Air leak in exhaust	Noise from under the hood, error appears after warming up. There may be a smell of exhaust gases in the cabin.	500–3,000 ₽ (replacement of gaskets/sealant)
Clogged or melted catalyst	Reduced power, “dullness” at high speeds. The error is not reset.	15,000–40,000 ₽ (replacement of catalyst or installation of flame arrester + blende)
Incorrect ECU firmware	The error appears after chip tuning. Possible “failures” during overclocking.	3,000–10,000 ₽ (flashing)

On Nissan Qashqai J11 (2014–2021) common false alarm P0420 due to the features of the firmware. In such cases it helps ECU software update from an official dealer or reflashing in a trusted tuning studio.

⚠️ Attention! If the error P0420 accompanied by code P0134 (“No oxygen sensor activity”) is most likely the culprit front lambda probe. In this case, start diagnosing there.

How to diagnose P0420 on a Nissan Qashqai yourself

For initial diagnosis you will need:

• 🔧 OBD-II scanner (For example, ELM327 or Launch CReader).
• 🔍 Multimeter (to check sensors).
• 🛠️ Endoscope (optional, for inspection of the catalyst).

Step 1: Read errors with the scanner

Connect the scanner to the connector OBD-II (located under the steering wheel, to the left of the pedals). Besides P0420, pay attention to the accompanying codes:

• P0130–P0167 — problems with lambda probes.
• P0300–P0306 — misfires (can destroy the catalyst).
• P0400–P0406 - system malfunction EGR (relevant for diesel engines).

Step 2: Check oxygen sensor readings

In mode Live Data look at the voltage graphs front And rear lambda probes:

• 🔹 Front sensor should fluctuate in the range 0.1–0.9 V (on a warm engine).
• 🔹 Rear sensor must be stable (~0.7 V) or fluctuate within a narrow range.

Check the associated errors with a scanner|Compare the readings of the front and rear lambda probes|Inspect the exhaust system for air leaks|Check the catalyst for clearance (with an endoscope or visually)|Reset the error and see if it returns-->

Step 3. Inspect the catalyst

On Qashqai with mileage >150 thousand km catalyst often melts or clogs. To check it:

1. Remove rear oxygen sensor.
2. Start the engine and see if there is exhaust pressure in the sensor hole (if it blows strongly, the catalyst is clogged).
3. Or dismantle the catalyst and inspect it against the light: honeycombs must be clean, without meltdowns.

How to check the catalyst without removing it?

If it is not possible to dismantle the catalyst, you can use back pressure test:

1. Unscrew spark plug (on petrol models) or pressure sensor (on diesels).

2. Insert into the hole compressor with pressure gauge and apply pressure ~0.5 bar.

3. If the pressure drops slowly, the catalyst is clogged.

What to do if the P0420 code does not reset

If you reset the error with the scanner, but it appears again after 50–100 km, the problem 100% hardware. Here's what to check first:

1. Replace the rear lambda probe

On Nissan Qashqai most often fails rear oxygen sensor (original article number - 22690-4M015). It can be replaced with an analogue (Bosch, Denso, NGK), but avoid cheap Chinese counterfeits - they may give incorrect readings.

2. Check the exhaust system for leaks

Air leakage after the catalyst (for example, through a crack in a corrugation or a burnt-out manifold gasket) leads to false sensor readings. Inspect:

• 🔧 Connection exhaust manifold with catalyst.
• 🔧 Corrugation (often cracks at mileage >100 thousand km).
• 🔧 Gasket exhaust pipe.

3. Install a decoy or emulator

If the catalyst already deleted (replaced with a flame arrester), but the error remains, you will need:

• 🔧 Mechanical snag (welded into the exhaust, moves the sensor away from the gas flow).
• 🔧 Electronic emulator (For example, CatSim or Lambda Emulator).

⚠️ Attention! On Nissan Qashqai with motors MR20DE (2.0 petrol) mechanical snags often don't work — The ECU “sees” the substitution. In this case you only need electronic emulator or firmware for Euro-2.

Replacing the catalyst on a Nissan Qashqai: original vs. station wagon

If diagnostics show that the catalyst melted or clogged, it needs to be changed. You have 3 options:

Option	Pros	Cons	Cost (₽)
Original catalyst	100% compatible, no errors	Very expensive, may clog again	30 000–50 000
Universal catalyst	Cheaper than the original, good quality	Requires welding, may have warranty issues	15 000–25 000
Flame arrestor + blende	The most budget option, does not require replacement	Not environmentally friendly, may not pass inspection	5 000–10 000

On Qashqai J10 (2007–2013) original catalyst costs ~40 000 ₽, but you can choose a universal analogue from Walker or Magneti Marelli for 15 000–20 000 ₽. For diesel versions (M9R) often requires replacement diesel particulate filter (DPF), which will cost 50 000–80 000 ₽.

Installation tip: if you install a universal catalyst, be sure to check that it is honeycomb size and shape matched the original. On Qashqai with motor HR16DE suitable catalyst with cells 400 cpsi (cells per square inch).

Error P0420 after chip tuning: what to do

If P0420 appeared after flashing the ECU (for example, to increase power), the problem is incorrect fuel maps. Chip tuning often makes a mixture richer, due to which the catalyst overheats and fails.

Solutions:

1. Return stock firmware and check if the error goes away.
2. If the catalyst is already damaged, replace it or install a blende.
3. Contact tuners for adjustment of fuel cards under Euro-2 (without catalyst).

On Nissan Qashqai with motor MR20DE often required after chip tuning disabling the rear lambda probe programmatically. This is done via:

• 🔧 Flashing the ECU (from official tuners).
• 🔧 Using the emulator (For example, Mini Maxi).

⚠️ Attention! If after chip tuning there are Misfire (P0300–P0306), the catalyst could melt down due to detonation. In this case it definitely needs to be replaced, otherwise ceramic dust will enter the cylinders and damage the engine.

Prevention of error P0420 on Nissan Qashqai

To avoid problems with the catalyst and lambda probes:

• ⛽ Refuel only at proven gas stations (bad gasoline destroys the catalyst).
• 🔧 Change spark plugs every 30,000 km (misfires kill the catalyst).
• 💨 Check cylinder pressure (low compression results in a rich mixture).
• 🔥 Don't Ignore Troubles P0300–P0306 (misfire = catalytic converter overheating).

On diesel Qashqai (M9R, R9M) follow:

• 🔧 Condition of the diesel particulate filter (DPF) - clean it every 80,000–100,000 km.
• 🔧 Operation of the EGR system — a clogged valve leads to increased fuel consumption and catalyst errors.

FAQ: Frequently asked questions about error P0420 on Nissan Qashqai

Is it possible to drive with P0420?

Short term - yes, but not recommended. If the catalyst is clogged, this leads to:

• 🔹 Increased fuel consumption (up to +2 l/100 km).
• 🔹 Loss of power (especially at speeds >3,000).
• 🔹 Risk of engine overheating (if the catalyst is melted).

If the error appeared recently and the car does not stall, you can drive to the service station, but it is better not to delay the repair.

How much does it cost to replace a catalyst on a Qashqai?

The cost depends on the type of engine and the chosen option:

• 🔧 Original catalyst: 30,000–50,000 ₽ (plus work ~5,000 ₽).
• 🔧 Universal catalyst: 15,000–25,000 ₽ (plus welding ~3,000 ₽).
• 🔧 Flame arrestor + blende: 5,000–10,000 ₽ (the most budget option).

On diesel versions (M9R) replacement diesel particulate filter (DPF) will cost 50 000–80 000 ₽.

Why does P0420 appear after replacing the catalytic converter?

The reasons may be as follows:

• 🔹 Poor quality universal catalyst (not compliant with Euro 5 standard).
• 🔹 Incorrect installation (for example, the oxygen sensor is located too close to the gas flow).
• 🔹 Air leak at the junction of the new catalyst with the exhaust system.
• 🔹 Faulty lambda probe (unless you replaced the old sensor).

Solution: check the tightness of the system and the quality of the installed catalyst.

Is it possible to deceive the ECU without cheating?

On some versions Nissan Qashqai (especially with a motor HR16DE) possible programmatically disable the rear lambda probe through the ECU firmware. However:

• 🔹 This does not work on all firmware.
• 🔹 Requires an experienced chip tuner.
• 🔹 May lead to problems with passing technical inspection (if environmental standards are disabled in the software).

A more reliable way is electronic snag (signal emulator).

Which scanner is best to use to diagnose P0420?

For Nissan Qashqai will fit:

• 🔧 Launch CReader VI+ — shows lambda probe graphs, supports Live Data.
• 🔧 ELM327 (Wi-Fi/Bluetooth) + application Torque Pro (budget option).
• 🔧 Autel MaxiCOM MK808 — professional scanner with advanced functions for Nissan.

For deep diagnostics (for example, checking fuel trims), it is better to use dealer scanner (Consult-III Plus).