Catalytic converter removal and P0420

Tags: #catalytic-converter · #ecu-tuning · #emissions · #rattle

Why owners remove it, and at what mileage. Many X80 owners remove the catalytic converters (there are two catalysts per car) once the check-engine light illuminates with a catalyst-related error code. Reported removal mileages in this batch: 70,000 km, 85,000 km, and 170,000 km. After removal, ECU reprogramming to the Euro-2 emission standard is generally required; some owners report the throttle response feels different (delayed) immediately after the remap. There is concern about catalyst fragments causing cylinder scoring if pieces break loose internally — this is debated within the community: some argue the risk is lower on the X80 than on some Korean-brand vehicles because of where the catalysts sit in the exhaust (one catalyst close to the manifold); KASPER specifically notes the catalyst closest to the manifold is the one whose debris could plausibly reach a cylinder. As an alternative to removal, replacing both catalysts costs 130,000+ RUB for parts, plus labor^12345678910. Conflict: Олег Белоусов argues catalyst fragments can cause cylinder scoring; Игорь Игорев argues the risk is minimal on non-Korean vehicles since debris exits via the exhaust; KASPER's middle position is that the catalyst nearest the manifold specifically could shed debris toward a cylinder.

ECU/lambda-sensor side of removal. Removing the catalyst requires one of two ECU-side approaches: (1) disable the lambda/oxygen sensor reading (the car runs Euro-2 logic on this platform), or (2) install an oxygen-sensor simulator ("обманка"). Using a simulator alone, without disabling the sensor logic, may not reliably prevent the check-engine light, depending on the simulator's calibration quality — most aftermarket simulators are reported unreliable, working initially but triggering the check-engine light again later. A professional ECU reflash is recommended for stable operation without a check-engine light^1112131415.

Removal without any ECU tuning at all — sometimes viable. The catalyst can be removed without any ECU reprogramming if the vehicle has no pre-existing error codes at the time of removal (confirmed by a diagnostic scan beforehand) — in that specific case, tuning is reported as unnecessary. However, even with a clean pre-removal scan, a check-engine light may still appear after 50,000+ km of subsequent driving. The engine will not stop running if the light activates, but the light stays on the dashboard. One owner reported driving 60,000+ km post-removal with no issues at all¹⁶¹⁷.

Deletion procedure and flame-arrestor replacement, at higher mileage. Catalytic converters are also removed around 112,000-120,000 km in some cases, with the converter physically replaced by a flame arrestor (пламягаситель) — shops performing this deletion keep the flame-arrestor part in stock. As above, tuning isn't always required immediately if the check-engine light doesn't illuminate right away, but ECU tuning (7,000-10,000 RUB, RU market, Feb 2025) is available to optimize engine behavior after deletion¹⁸¹⁹²⁰.

Non-destructive inspection method (avoids guessing whether removal is even needed). Catalytic-converter interior condition can be checked without removing the part, using an endoscope inserted through the oxygen-sensor ports (located before and after the catalyst). This lets an owner assess internal deterioration or damage before deciding whether to remove or replace. A properly functioning catalyst can reportedly remain in service 200,000+ km without visible degradation when combustion stays clean²¹²²²³.

P0420 code specifically. The P0420 code ("Catalyst System Efficiency Below Threshold, Bank 1") indicates either catalyst failure or a malfunctioning second (downstream) lambda sensor. Two solution paths: (1) check/replace the second lambda sensor and its wiring, or (2) delete the catalyst with an ECU remap and install a flame guard — one reported price point was 5,000 RUB in Samara, as of April 2024 (RU market). Owners report improved power/performance after catalyst deletion for this code; the vehicle remains drivable with the check-engine light on^2425262728.

Exhaust-system fastener corrosion (separate, related maintenance note). Around 250,000 km, the bolts and spring fasteners holding the exhaust system together typically corrode and can shear/lose their heads during removal attempts; using an impact wrench (ударный гайковёрт) is reported to solve the extraction problem — without one, bolt heads often just break off²⁹.

Euro 5 firmware perceived as restrictive — Euro 2 downgrade for performance. Community perception is that the X80's Euro 5 firmware calibration is restrictive and limits engine performance for emissions compliance. Some owners downgrade to Euro 2 firmware for better throttle response and power delivery, trading emissions control for performance³⁰³¹.

Stage 1 tuning without catalyst deletion — price point. Stage 1 ECU tuning that does not remove/delete the catalytic converter was available in Nizhny Novgorod for 12,000 RUB as of June 2025 (RU market)³².

Catalyst error diagnosis at low mileage. At 57,000 km, outright catalytic converter failure is considered rare on a stock vehicle. If a P0420-type cat-related code appears, check the oxygen (lambda) sensor first with a diagnostic scanner/multimeter before assuming the catalyst itself has failed — specifically the second, post-catalyst sensor. Chinese-vehicle catalytic converters are reported to have a more limited lifespan compared to other manufacturers^{33343536373839}.

Custom ECU remap — O2-sensor disable plus power tuning, a tuner's perspective. A tuner reports the standard remap program disables oxygen-sensor monitoring (supporting catalyst delete/bypass, consistent with the lambda-defeat approaches already documented on this card) and can additionally adjust engine power characteristics on request. A common customer request is more power in the low/mid RPM range; one tuner mentioned adding power there specifically because the car is mostly driven by their spouse⁴⁰.

Secondary (post-lambda) catalyst removal — disputed practice, restated with more detail. The secondary catalytic converter (positioned after the second lambda sensor) can be removed and replaced with a welded-in flame suppressor, typically paired with an ECU reprogram to clear the resulting error codes — consistent with the general catalyst-deletion procedure already documented on this card. Removal before 100,000 km is recommended to limit catalyst breakdown and the resulting risk of metal debris scoring the engine. Dispute: some owners advocate removal for performance/engine-longevity reasons, while others — specifically Chinese-market tuners — advise against removal on Chinese-built engines, citing lower durability margins than the donor Mazda/Ford design. An alternative to full removal: install a repair/restoration catalytic converter without any ECU reprogram^{414243444546474849505152535455565758}. Conflict: one owner removed the secondary catalyst at 80,000 km after an error code and reported improved performance; another reports catalyst clogging/failure starting at 58,000 km, resolved via removal plus reprogram; the community's rough consensus is to remove only if an error code actually appears, ideally before 100,000 km.

Claimed factory power output — 164 hp design vs. 142 hp as delivered. Per Chinese-tuner sources, the X80's engine (Mazda/Ford-derived) is rated 164 hp in its parent design but intentionally throttled to 142 hp from the factory. An ECU reprogram is claimed to recover roughly 12-15 hp (~10%). Conflict: some tuners (Chinese chip-tune shops) say the factory ECU is already at its practical maximum and advise against remapping; others report a remap mainly improves throttle response and lets the driver customize pedal sensitivity without exceeding safe engine limits — one owner reports 4 years of remap use with no issues, and another states the remap doesn't touch core fuel/timing maps, only removes factory throttle limiters. A related, unresolved debate concerns motor longevity: Mazda/Ford-original engines are assumed good for 1M+ km, while the Chinese-built copies are assumed by some to top out around 300,000-400,000 km^{555960616263646566}.

Chip-tuned AT behavior — even a mild 95-octane remap affects shifting. Even a slight chip tune (a remap for 95-octane fuel mapping) is reported to change automatic-transmission behavior: the transmission can start hunting between gears and become overly sensitive to throttle input — hyper-responsive at intermediate throttle, sluggish under higher load. The reporting owner does not recommend a 95-octane remap given concerns about both engine and transmission resource/durability^{67686970717273}.

ECU block/firmware variation across production batches. X80 ECU hardware blocks are inconsistent across production batches — different blocks need different firmware and tuning approaches, and standard Mazda/Ford tuning software does not reliably support every X80 block because of this variation. The ECU can be read and reprogrammed, but matching firmware is hard to find in public databases; tuners sometimes resort to loading Mazda or Ford firmware as a workaround, with inconsistent results. This block-to-block inconsistency is described as unusual and specific to FAW's production process^74757677.

Removal + flame-arrestor retrofit — cost breakdown restated with sourcing options. When a clogged catalyst needs removal: replacement-unit options include a new unit (~35,000-40,000 RUB used, RU market, Oct 2025), a 16,500 RUB alternative (Nissan Qashqai Euro 5 catalyst via Avito), or a universal 63.5mm unit from AliExpress (~1,676 UAH). Alternatively, remove the catalyst and install a flame arrestor (пламегаситель) plus reflash the ECU: reported costs (RU market, Oct 2025) were 5,000-12,000 RUB for tuning, 2,000-5,000 RUB for flame-arrestor welding, and one report of 5,000 RUB total in Samara two years prior. After removal with a correct reflash, expect at most a minor oil smell at startup; without reflashing, the engine over-consumes oil. A chemical catalyst-cleaner fuel additive exists but has limited effectiveness^{787980818283848586878889}. Conflict: side-effect reports disagree — some owners see no oil consumption after removal+reflash, others report a slight oil odor or minimal consumption.

Removal procedure detail — manifold gasket risk, honeycomb inspection, and a repair-converter price point. Removing the catalyst requires removing the exhaust-manifold gasket, which can break during extraction. Before removal, inspect the ceramic honeycomb inside (white ceramic with light passing through = partial blockage but usable; dark/broken sections = failure) to judge whether removal is even necessary. After removal, install a flame arrestor to maintain exhaust safety. A Euro-5 repair converter was available for roughly 8,800 RUB (RU market, Nov 2025, Yandex Market) as a lower-cost alternative to a full new unit — one reported case of proactive removal without any prior failure symptoms^{90919293949596979899100101102103104105106107108109110111112113114115}.

Two-catalyst layout confirmed again. Restating the two-catalyst layout already documented on this card: the X80 has two catalytic converters in the exhaust system, and each can trigger its own independent error code¹¹⁶.

Internal substrate degradation at 121,000 km — no external symptoms. At 121,000 km, internal degradation of the catalyst substrate can begin — the ceramic honeycomb material starts to crumble/flake internally, which may trigger intermittent fault codes. Critically, external inspection alone can show no visible damage or clogging; the deterioration is purely internal and would only be caught by the endoscope method or a substrate check already documented on this card^117118119120.

ECU remap + cat removal — 2026 price point and driver feedback. A combined catalyst-removal-plus-remap service (to the Euro-2 map, consistent with the general approach already documented on this card) was quoted at roughly 8,000 RUB (RU market, Mar 2026) for automatic-transmission cars. Owners report the car feels noticeably more responsive ("резвее, шустрее") after the combo, with a slight morning exhaust smell that dissipates and disappears — a flame suppressor is recommended to manage this. Concerns raised: increased engine load, the automatic transmission may shift harshly at first as it adapts, and an oil change is recommended right after remapping. Longevity reports: one owner has run 120,000-190,000 km since removal with no engine issues; another reports satisfactory performance overall. Conflict (consistent with the tuner dispute already documented on this card): tuners warn that adding power stresses the automatic transmission and requires careful adaptation, while some owners report no issues at all^{121122123124125126127128129130131132133134135136137}.

P0420 at ~140,000 km — diagnosis path and a caution against catalyst specialists. After a check-engine light and P0420 diagnosis at ~140,000 km, recommended diagnosis (before assuming the catalyst is dead): use an endoscope to physically inspect the catalyst substrate for soot buildup, melting, or physical breakup; pull and inspect the oxygen sensors, which can simply be clogged; and try sustained highway driving at higher RPM ("give it some gas") to burn off accumulated soot, since low-speed/short-trip driving is what lets soot build up in the first place — mileage alone is not the determining factor, driving style is. Only if the endoscope shows the substrate melted or physically disintegrated should removal be considered. One owner in this thread had recently installed a methane (CNG) conversion, adding a possible contributing variable. Repair-shop skepticism: "catalyst specialists" are said to have a financial incentive to recommend deletion regardless of actual condition, so their diagnosis should not be taken at face value. Self-diagnosis tooling recommended: an ELM327 v1.5 Bluetooth scanner with the dual-board PIC18F25K80 chipset, ~800 RUB (RU market, Apr 2026) on Ozon, to let owners read/monitor codes themselves rather than relying solely on a shop^{138139140141142143144145}.

P0420 traced to poor-quality fuel — Gazprom vs. Rosneft, repeatable. A separate P0420 case: the check-engine light and P0420 code appeared, was cleared, and then reappeared while running out a tank of Gazprom 95-octane fuel purchased in late April 2026. After switching to Rosneft 95-octane, the code cleared and did not return after roughly 45-60 km of driving — confirmed as resolved by a follow-up scan showing no codes. A similar case from a Chery-brand owner reportedly showed an "insufficient octane rating" message on the same Gazprom fuel. Community consensus in this thread: Gazprom-brand fuel quality is a recurring complaint (some say Gazprom stations prioritize their gas/LPG business over petrol quality), and Rosneft, Gazpromneft (a distinct company from Gazprom despite the similar name), or Tatneft are recommended as more reliable fuel sources — one long-time member reports exclusively using Teboil or Rosneft^{146147148149150151152153}.

Rattle from corroded mounting bolts — causes and repair options. A separate rattle symptom, distinct from the codes/removal cases above: the lower catalytic converter can rattle due to corroded mounting bolts. Recommended solution path: (1) check the screen/mesh on the second catalyst (afterburner); (2) remove the corroded mounting bolts — reported repair cost around 1,000 RUB (RU market, Aug 2026); (3) optionally install a flame arrestor after removal, consistent with the flame-arrestor practice already documented on this card; (4) install an ECU "cheat"/simulator module or get a full reprogram. Reported reprogramming price spread by region (RU market, Aug 2026): Tula region 8,000 RUB, Orel 15,000 RUB, Moscow 20,000 RUB — a notably wide regional spread compared to the other remap prices already on this card. The ECU on these cars is a Bosch 7.8.8 unit, which is described as having limited reprogramming options available compared to other ECU families^{154155156157158159160161}.

Front catalytic converter cut out — owner report from Perm (Oct 2026). Konstantin Руммель cut out the front catalytic converter (катализатор) at "40k" (unit not stated, presumably km) and says the car feels great ¹⁶²¹⁶³. He left the rear converter in place so the cabin does not smell of exhaust ¹⁶⁴. A question whether removing the rear one would matter, and one about chip tuning (чип-тюнинг), received no answer in the batch.

Media

Photo of removed catalytic converter interior showing ceramic honeycomb structure

OBD-II scanner screenshot showing error code P0420: Catalyst System Efficiency Below Threshold (bank 1)

Photo of exhaust manifold gasket with a corner broken during removal

Photo showing the P0420 error code definition and diagnostic reference information

Additional photo of P0420 diagnostic reference information

Video showing intact external catalyst substrate with no obvious blockage, despite internal degradation at 121,000 km

Related pages

• Catalytic converter failure — P0420/P0430 codes
• Catalytic converter removal — ECU reflash
• ECU diagnostic tools — Diagon/Launch vs OBD
• OBD diagnostic scanners, software, and TPMS tools
• ELM327 Bluetooth adapter — setup and X80 coverage

Sources

This page is compiled from 164 community messages. Every fact carries a numbered reference to its original author and message.

Last updated: 2026-10-29