Car won't start after catalytic converter theft

Symptoms

• Extremely loud exhaust or roaring sound when the engine runs (if it starts at all)
• Visible damage or a gap under the car where the converter used to be
• May cough, stall, or refuse to start
• Check engine light likely on

Likely causes

• CommonDamaged oxygen sensor wiring cut during the theftThieves often cut wiring along with the converter, damaging sensors the engine needs to run correctly.
• CommonExhaust system damage affecting backpressure and sensor readingsRemoving the converter changes exhaust flow enough to trigger fault codes and rough running.
• PossibleDamaged fuel or electrical lines running near the converterSome vehicles route other lines near the exhaust, which can be damaged during a hasty theft.
• PossibleUnrelated coincidental no-start issueSometimes a separate issue coincides with noticing the theft.
• PossibleEngine control system defaulting to a protective mode from sensor faultsSeverely disrupted sensor data can cause some vehicles to run very poorly or not start.

What to do

1. Do not attempt to drive the car if you notice extremely loud exhaust noise or see an obvious gap under the vehicle; inspect first.
2. Photograph the damage underneath the car for a police report and insurance claim before any repair.
3. File a police report and contact your insurance company, since catalytic converter theft is often covered under comprehensive coverage.
4. Check for any dangling or cut wiring near the damaged area that might explain a no-start beyond the missing converter.
5. Avoid running the engine for extended periods with the converter removed if you can help it, since it's very loud and technically illegal to drive that way in most areas.
6. Have a muffler or exhaust shop assess the full extent of damage, including any cut sensors or wiring.
7. Get the oxygen sensor wiring repaired along with the converter replacement, since a car often won't run well with damaged sensor wiring even after a new converter is installed.
8. Consider a catalytic converter anti-theft device once repaired, since vehicles that have been targeted once are sometimes targeted again.

Tools and parts

When to call a pro

Catalytic converter theft repair, including any related wiring damage, should be handled by an exhaust or general repair shop, ideally coordinated with your insurance claim.

Safety