Error code P0420 on Nissan Qashqai - one of the most common problems faced by owners of gasoline versions (especially with engines HR16DE, MR20DE And M9R). This code indicates low catalytic converter efficiency, but in practice the reasons may lie far beyond the catalyst itself. In 80% of cases, the error occurs due to related faults - from air leaks to problems with lambda probes.

If the dashboard lights up Check Engine, and the scanner showed P0420 with parameter "Bank 1" (first row of cylinders), do not rush to change the catalyst right away. In this article we will look at:

  • 🔍 Real reasons errors (not just “clogged catalyst”)
  • 🛠️ Step-by-step diagnostics without a service station - what you can check yourself
  • 💰 Repair cost in 2026 (from removing the catalyst to replacing lambda probes)
  • ⚠️ Consequences of ignoring P0420 for engine and ecology

The article is based on data from service manuals Nissan, owner experience Qashqai J10/J11 and recommendations of diagnosticians. All instructions are adapted for Russian conditions (including fuel and climate characteristics).

What does error code P0420 mean on Nissan Qashqai?

Code P0420 stands for "Catalyst System Efficiency Below Threshold (Bank 1)". Translation: the efficiency of the catalyst of the first row of cylinders is below the permissible threshold. But why is this happening?

Catalytic converter (catalyst) in Qashqai is responsible for cleaning exhaust gases from harmful substances: CO (carbon monoxide), NOx (nitrogen oxides) and CH (hydrocarbons). The engine ECU compares the readings two oxygen sensors:

  • 🔹 Upper (lambda probe 1) — before the catalyst (measures “dirty” exhaust)
  • 🔹 Lower (lambda probe 2) — after the catalyst (measures “cleaned” exhaust)

If the difference in sensor readings is less than expected, the ECU records an error. Normal catalyst should reduce the level of harmful substances by 90-95%. With P0420 this value drops below 70-80%.

⚠️ Attention: On Nissan Qashqai with diesel engines (M9R, R9M) code P0420 is less common, but is diagnosed in a similar way. The main reason is a malfunction of the particulate filter (DPF) or sensor NOx.

Top 5 causes of error P0420 (not only the catalyst!)

Most technicians immediately suggest replacing the catalyst, but 60% In some cases, the problem lies elsewhere. Here are the real reasons, ranked by frequency:

  1. Malfunction of lambda probes (especially the lower one). The sensor may lie due to:
    • 🔥 Overheating (if the catalyst is clogged, exhaust gases heat the sensor to 900°C+)
    • 🛢️ Contamination with fuel additives or oil (if the engine “eats” oil)
    • 🔌 Broken wiring or oxidation of contacts (check the connector on the collector!)
  2. Air leak after the catalyst. The ECU sees a "diluted" mixture and records a false inefficiency.
  3. Clogged catalyst (really only in 30% cases). Signs: loss of power, popping sounds in the exhaust system, sulfur smell.
  4. Problems with the fuel system:
    • ⛽ Bad fuel (high sulfur content destroys the catalyst)
    • 🔧 Faulty injectors (fuel overflow → rich mixture → catalyst overheating)
  • ECU firmware. On Qashqai J11 (2014+) there are firmware “curves” where the P0420 response threshold is too low.
    • Reason Symptoms Repair cost (₽)
    Faulty lambda probe (lower) P0420 + P0130/P0150, high fuel consumption 2 500–6 000
    Air leak P0420 + P0171/P0174, rough idle 500–3,000 (replacement of gaskets/clamp)
    Clogged catalyst Loss of power, popping noises, rotten egg smell 15,000–40,000 (replacement) or 5,000–10,000 (removal + blende)
    Bad fuel/additives P0420 after refueling, black carbon deposits on spark plugs 0 (flushing the system) or 2,000 (replacing spark plugs)
    📊 How long have you had the P0420 code?
    • Less than a week
    • 1–3 months
    • More than 6 months
    • Constantly (already resigned)

    How to diagnose P0420 on a Nissan Qashqai yourself

    Before going to the service station, go through this checklist. 50% Problems can be solved without disassembling the engine!

    Check the lambda probe circuit (with a multimeter: heater resistance 2–10 ohms)

    Inspect the exhaust system for cracks/burnouts (especially the junction of the catalyst with the resonator)

    Reset the error and drive 100-150 km - if P0420 returns, the problem is serious

    Check the fuel pressure (with a pressure gauge on the rail) - it should be 3.5–4.0 bar

    Fill with high-quality fuel (for example, Gazpromneft G-Drive 98) and add injector cleaner (Liqui Moly)

    Step 1. Checking the lambda probes

    The lower sensor (after the catalyst) most often lies. How to check it:

    1. Remove the connector from the sensor and check the heater voltage (contacts 3 And 4 on Qashqai J10): must be 10–12 V with the ignition on.
    2. Measure the resistance of the heater (contacts 3–4): normal 2–10 ohms. If ∞ - break if 0 - short circuit.
    3. Check the signal wire (pin 1): when the engine is running, the voltage should fluctuate in the range 0.1–0.9 V.

    Step 2. Air leak test

    Use smoke tester or improvised means:

    • 🔧 Pinch the crankcase ventilation hose (goes from the valve cover to the intake manifold). If the error disappears, look for cracks in the hoses.
    • 🧼 Soap the joints of the exhaust system (from the manifold to the resonator). If bubbles appear somewhere, there is a leak.
    How to check the catalyst without removing it?

    Remove the upstream oxygen sensor and replace it with a pressure gauge. Start the engine and accelerate to 3,000 rpm. If the pressure in front of the catalyst exceeds 0.3–0.5 bar, and after it drops to 0, the catalyst is clogged. If the pressure is equally low, the catalyst is “empty” (burnt out or removed).

    Step 3: Fuel System Analysis

    If the lambda probes and catalyst are ok, check:

    • 🛢️ Fuel pressure: Connect the pressure gauge to the fuel rail. Norm for HR16DE — 3.5–4.0 bar.
    • 🔥 Condition of the candles: black soot indicates a rich mixture, white soot indicates a poor mixture.
    • 📊 Short trips: if you only drive short distances, the catalyst does not warm up to operating temperature (400°C+) and becomes “clogged” with soot.
    💡

    On Nissan Qashqai with motor MR20DE The P0420 error often appears after replacing the exhaust system with a non-original one. The reason is the incorrect location of the lower lambda probe (it should be strictly after the catalyst, and not in the resonator!).

    What to do if error P0420 is confirmed?

    Depending on the reason, there is 4 solutions:

    1. Replacing lambda probes

    If the sensors are faulty, they need to be replaced. Important:

    • 🔧 Use only original sensors (Nissan 22690-4M000 for the top, 22690-4M010 for the lower one) or high-quality analogues (Bosch, Denso).
    • ⚠️ Do not buy universal sensors - they often lie and cause P0420 again.
    • 🛠️ When replacing, lubricate the sensor thread graphite lubricant (so as not to stick).

    2. Cleaning or replacing the catalyst

    If the catalyst is clogged:

    • 🧹 Flushing: You can try catalyst cleaner (Hi-Gear HG3270). Fill the fuel tank, drive 50–100 km at high speeds (3,000–4,000 rpm). Efficiency: 20–30% (helps only with light contamination).
    • 🔄 Replacement: original catalyst for Qashqai worth it 30 000–50 000 ₽. An alternative is a universal catalyst (Walker, Magnum) for 15 000–25 000 ₽.
    • ⚠️ Removal: cheapest (5 000–10 000 ₽), but requires installation decoys (mechanical or electronic). Without cheating, the ECU will constantly issue P0420, and on new versions Qashqai J11 (2017+) emergency mode may be activated.

    3. Elimination of air leaks

    Most often, air is sucked in through:

    • 🔩 Cracks in exhaust manifold (especially on Qashqai J10 with mileage 150,000+ km).
    • 🔄 Gasket catalyst (check the bolts - they often come loose).
    • 🧯Hose crankcase ventilation (over time it becomes dull and cracks).

    4. ECU firmware

    On Nissan Qashqai J11 (2014–2021) there are “buggy” firmwares where the P0420 response threshold is too low. Solution:

    • 📥 Update the ECU software to the latest version (at the service station, cost 3 000–5 000 ₽).
    • 🔧 If the update does not help, roll back to the previous firmware version (sometimes it helps).
    ⚠️ Attention: If you decide to remove the catalyst, please note:
    1. Since 2023, Russia has tightened control over the environmental class. A car without a catalyst may not pass inspection.
    2. On Qashqai with motor M9R (diesel) removing the catalyst often leads to an error P2002 (clogged particulate filter).

    How much does the repair cost? Prices 2026

    The cost depends on the reason and region. Below are the average prices for Nissan Qashqai J10/J11:

    Type of repair Cost (₽) Deadline (hours) Warranty
    Diagnostics (scanner + sensor check) 1 500–3 000 1–2 —
    Replacing the lower lambda probe 2,500–6,000 (with work) 0.5–1 6–12 months
    Removing the catalyst + blende 5 000–12 000 2–3 1 year (for welding)
    Replacing the original catalyst 30 000–50 000 3–4 2 years
    Cleaning injectors + replacing spark plugs 8 000–15 000 2–3 6 months

    Where is it cheaper?

    • 🔧 Service station: Diagnostics 1 500–3 000 ₽, but they give a guarantee.
    • 👨‍🔧 Private masters: Cheaper at 20–30%, but there is a risk of running into an amateur.
    • 🛠️ On your own: If you know how to use a scanner and a multimeter, you can do it in 2 000–5 000 ₽ (spare parts + snag).
    💡

    The best solution for P0420 is to first check the lambda probes and air leaks. In 60% of cases, the problem is solved for 2,000–5,000 rubles without replacing the catalyst.

    What happens if you ignore the P0420 code?

    Many owners Qashqai drive with the light on Check Engine years, but the consequences can be serious:

    • 🚗 For engine:
      • ⚠️ If the catalyst is clogged, the pressure in the exhaust system increases → the engine “suffocates” and loses power.
      • ⚠️ Rich mixture (due to faulty sensors) leads to overheating And maslozhora.
    • 💨 For the environment:
      • ⚠️ The emission of harmful substances increases in 5–10 times (especially CO And NOx).
      • ⚠️ In some regions (Moscow, St. Petersburg) they are fined for this (5 000 ₽ according to Art. 8.23 Code of Administrative Offences).
    • 📉 For wallet:
      • ⚠️ Fuel consumption increases by 10–15% (The ECU goes into emergency mode).
      • ⚠️ When selling a car, the price drops by 20–30 000 ₽ (buyers are afraid of environmental problems).

    Is it possible to drive with P0420? Short term - yes, but:

    • 🚦 If there are no other symptoms (power loss, popping noises), you can postpone the repair until 1–2 months.
    • ⛽ If the engine runs rough or lights up Check Engine constantly - repairs are needed urgently.

    FAQ: Frequently asked questions about error P0420 on Nissan Qashqai

    ❓ Is it possible to reset the P0420 error without repair?

    Yes, but she'll be back in 50–200 km. A reset only helps for diagnostics: if the error appears again, the problem is real. Use a scanner (ELM327) or disconnect the battery terminal for 10 minutes.

    ❓ What other errors can come with P0420?

    Frequent "companions":

    • P0130/P0150 — faulty lambda probe 1/2.
    • P0171/P0174 — lean mixture (air leaks).
    • P0300 — misfires (may cause destruction of the catalyst).

    ❓ Which catalyst is better to install on Qashqai: original or analogue?

    Depends on budget:

    • Original (Nissan 205B0-4M000): expensive (30 000–50 000 ₽), but serves 150,000+ km.
    • Analogue (Walker, Magnum): cheaper (15 000–25 000 ₽), but may not pass eco-standards Euro 5.
    • Universal: the most budget option (8 000–12 000 ₽), but requires welding.

    ❓ Does cleaning the catalyst with Hi-Gear type fluids help?

    Helps only with light soiling (for example, after refueling with bad gasoline). If the catalyst is melted or destroyed - only replacement. How to clean:

    1. Pour cleaner into the fuel tank (on 40–50 l gasoline).
    2. Drive 100 km at speed 3,000–4,000 rpm (highway, not city!).
    3. Repeat 2-3 times.

    Success: 20–30% (according to owner reviews Qashqai on Drive2).

    ❓ Is it possible to flash the ECU so that error P0420 does not appear?

    Technically yes, but:

    • ⚠️ This is illegally — violates eco-standards.
    • ⚠️ On Qashqai J11 (2017+) after such firmware it may catch fire Check Engine with other errors.
    • ⚠️ The cost of firmware “for Euro-2” is 10 000–15 000 ₽.
    It's better to eliminate the cause!