Exhaust & emissions · Sant Andreu
Catalytic converter cleaning and repair in Barcelona
Engine light with a P0420 code, loss of power on the motorway or a rotten-egg smell: we diagnose whether the converter is blocked, aged or simply in bad company, and recover it with cleaning whenever the ceramic allows it.
Tallers Marathon is a multi-brand garage in Sant Andreu (Carrer del Vallès 47, 08030 Barcelona). We handle catalytic converter faults for drivers from Sant Andreu, La Sagrera, Bon Pastor, Trinitat Vella and Navas, with a fixed, free quote and a written warranty.
What does this service include at Tallers Marathon?
Diagnosis with both lambda sensors and live data, converter cleaning when it is recoverable, and a homologated replacement with a fixed quote when it is not.
- Diagnosis of the real faultWe compare sensors, measure back pressure and rule out leaks before blaming the converter.
- Converter cleaningChemical treatment or off-car cleaning depending on the degree and type of blockage.
- Cause correctedRich mixture, oil or coolant in the exhaust: whatever poisoned the converter gets repaired.
- Ready for the ITVFinal emissions check and fault clearing with a road test.
A blocked catalytic converter: what happens and how it feels
The converter turns CO, HC and NOx into inert gases as the exhaust flows through its cells; when carbon, oil or an impact block them, the engine chokes and emissions soar.
P0420 deserves its own paragraph because it is the most misread code in the exhaust. The ECU raises it when the rear lambda sensor "sees" almost the same as the front one, a sign the converter is barely converting. But a lazy lambda sensor, a small leak upstream of the sensor or an unbalanced mixture produce exactly the same reading with a healthy converter. Replacing the converter without checking this is throwing money away: our diagnosis rules it out first, and only then do we talk about cleaning or replacing.
Cleaning or replacement? How we decide
Cleaning recovers converters that are blocked but intact: carbon from short trips, residues from poor combustion or early-stage oil traces. A specific chemical treatment is applied — on the car or with the part removed, case by case — and the result is verified by measuring back pressure and efficiency. It is fast, economical and avoids replacing one of the most precious-metal-rich parts of the car.
Replacement is reserved for irreversible damage: a monolith melted by prolonged misfires, crumbled ceramic that rattles, or poisoning by lead, silicone or coolant. We always fit homologated converters for your exact engine; universal units of dubious origin do not last and tend to come back with the same P0420. There is more detail on the replacement on the catalytic converters page.
And the usual warning: we do not gut converters or fit straight pipes for use on public roads. It is illegal, an automatic failure at the ITV emissions test, and turns every start-up into a cloud of untreated gases. If the problem is money, cleaning exists precisely for that.
Our process, step by step
- Codes and live data. Fault codes, signals from both lambda sensors and converter temperature while running.
- Physical checks. Exhaust back pressure, leak inspection and gentle tapping to detect loose ceramic.
- Root cause. We review mixture, ignition and oil or coolant consumption: whatever dirtied the converter would dirty it again.
- Cleaning. Chemical treatment on the vehicle or off-car cleaning, depending on blockage; efficiency verified afterwards.
- Homologated replacement if needed. With a prior fixed quote, fitting of a homologated converter, new gaskets and a final emissions test.
The ITV emissions test — opacity for diesels, CO and lambda for petrols — has no mercy on an inefficient converter, so if your inspection is close it pays not to cut it fine. On diesels, converter and filter work in series: if your fault comes with a DPF light, also look at particulate filter cleaning or, where there is physical damage, particulate filter replacement. For engines with heavy carbon build-up, engine decarbonisation reduces the dirt reaching the exhaust. And for anything else, contact the garage directly.
Frequently asked questions about the catalytic converter
What does fault code P0420 mean?
That the ECU has detected low catalytic converter efficiency by comparing the two lambda sensors. It is not always the converter: an ageing sensor, an exhaust leak or an incorrect mixture produce the same code. That is why we diagnose before quoting.
Can a catalytic converter be cleaned, or does it always need replacing?
If it is blocked by carbon or residues and the internal ceramic is intact, cleaning can recover it. If the monolith is melted, crumbled or contaminated by oil or coolant, the only lasting solution is replacing it with a homologated unit.
What are the symptoms of a blocked catalytic converter?
Power loss especially at high revs, hesitation, high consumption, a rotten-egg smell and, if the ceramic has broken loose, a metallic rattle under the car. With severe blockage the car can even stall or refuse to start.
Will I pass the ITV with the engine light on because of the converter?
No: the inspection includes reading the warning lights and an emissions test, and an inefficient converter sends CO and HC values through the roof. Repairing before the appointment is the only realistic way to get a pass.
Is it legal to remove the catalytic converter or fit a straight pipe?
Not for driving on public roads: it is an illegal modification, a straight ITV failure and multiplies emissions. At Tallers Marathon we do not gut or delete catalytic converters; we clean them or replace them with homologated parts.
How much does catalytic converter cleaning cost?
It depends on the degree of blockage and whether it is done on the car or with the part removed. After the diagnosis we give you a fixed, free quote; if cleaning were not viable, we quote the homologated replacement before doing anything.
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