Exhaust, fuel & emissions

Catalytic converter clogged, car has no power

A clogged catalytic converter chokes off exhaust flow, which starves the engine and causes a big loss of power, a rotten-egg smell, and often a check engine light with a code pointing at converter efficiency.

Difficulty
Professional only
Time
1–3 hours
Pro cost
$300–$2500

Symptoms

  • Noticeable loss of power, especially uphill or accelerating
  • Engine feels like it's being held back
  • Rattling sound from underneath (broken internal honeycomb)
  • Rotten egg or sulfur smell from the exhaust
  • Check engine light with a converter efficiency code

Likely causes

  • CommonClogged catalytic converterAge, a rich-running engine, or oil/coolant burning can coat and clog the internal honeycomb.
  • CommonUnderlying engine problem causing the clogA misfire, bad spark plugs, or a leaking injector can dump unburned fuel into the converter and damage it.
  • PossiblePhysically broken/collapsed internal substrateImpact damage or age can crumble the ceramic honeycomb inside, partially blocking flow.
  • PossibleFailing oxygen sensor giving bad readingsA bad sensor can cause the engine to run rich, accelerating converter damage.

What to do

  1. Note when the power loss happens (all the time vs. only under load) and whether a check engine light is on.
  2. Have the check engine light scanned; a code like P0420 or P0430 points specifically at converter efficiency.
  3. Ask a shop to check for exhaust back-pressure or physically inspect the converter for a clog or rattle.
  4. Fix any underlying misfire, bad spark plug, or fuel system issue first, since replacing a converter without fixing the root cause often leads to a repeat failure.
  5. Replace the catalytic converter if it's confirmed clogged or damaged.
  6. Recheck the engine light and take a short test drive to confirm normal power has returned.

Tools and parts

  • OBD-II code reader
Replacement catalytic converterSearch: “catalytic converter for [year make model]”
Oxygen sensorSearch: “oxygen sensor for [year make model]”

When to call a pro

See a repair shop for diagnosis and replacement; they can confirm the clog with back-pressure testing and address any underlying cause so the new converter lasts.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.