Catalytic converter failure: symptoms and cost

The catalytic converter (catalyst) converts harmful exhaust gases into less polluting ones. When it degrades or blocks, the symptoms are often clear. Here are the signs and costs to expect.

Common symptoms

Noticeable loss of power, engine spluttering under acceleration. Engine warning light on (lambda sensor or catalyst). Rotten egg smell (sulphur) from the exhaust. Metallic noise or vibration if the catalyst is damaged or loose. High fuel consumption possible.

Common causes

Clogging (rich mixture, faulty plugs or injection, oil entering combustion). Overheating (carbon, misfires). Impact or corrosion (hole, broken core). An oil-burning engine or prolonged misfires can damage the catalyst.

What to do

A diagnostic (fault codes, lambda check) confirms. If the catalyst is blocked or faulty, replacement is often needed. Driving with a faulty catalyst can damage the engine and is illegal (emissions test).

Order of magnitude for costs

Catalytic converter (part): €300–1,500 and more depending on vehicle. Labour: €150–400. Lambda sensors (if replaced): €100–300. Total often €500–2,000 and more. My Auto Check-up helps you prepare your garage visit for a cost estimate.