Catalytic converter failure: symptoms and cost

The catalytic converter converts harmful exhaust gases into less polluting ones. When it degrades or clogs, the symptoms are usually pretty clear. Here are the signs and costs to expect — and why this part is worth paying attention to in the US specifically.

Common symptoms

Noticeable loss of power, engine sputtering under acceleration. Check engine light on (oxygen sensor or catalytic converter code). Rotten-egg smell (sulfur) from the exhaust. Rattling noise if the converter's internal honeycomb has broken up, or a loud, sudden increase in exhaust noise if the converter has been physically removed. Higher fuel consumption is also possible.

Common causes

Clogging (rich fuel mixture, bad spark plugs or injectors, oil burning into the exhaust). Overheating (carbon buildup, misfires). Physical damage (road debris, corrosion, a cracked core) — or, increasingly common in the US, catalytic converter theft, since converters contain valuable precious metals and can be cut out from under a parked vehicle in minutes. Toyotas, Hondas and trucks with higher ground clearance are frequent targets. A misfiring or oil-burning engine can also damage the converter over time.

What to do

A diagnostic (trouble codes, oxygen sensor readings) confirms the cause. If the converter is clogged or stolen/damaged, replacement is usually necessary — driving without a working catalytic converter fails emissions testing in most states and can also damage the engine over time. If you park outside regularly, an aftermarket anti-theft shield is a cheap way to lower the risk of losing the part to theft in the first place.

Order of magnitude for costs

Catalytic converter (part): $600–2,500 and more depending on vehicle (higher for Toyotas and Hondas due to demand from theft replacements). Labor: $150–400. Oxygen sensors (if also replaced): $150–400. Anti-theft shield (prevention): $150–300 installed. Total repair after a theft is often $1,000–3,000 and more. My Auto Check-up helps you prepare for your shop visit with a cost estimate.