Removing the catalytic converter (decat, uncertified downpipes) — illegal, no exceptions
Decat downpipes or full catalytic converter removal are popular for the sound and a slight power bump. Unlike most other modifications, though, this one is illegal with no exceptions — no assessment or registration can legalize it.
Why it's illegal
The catalytic converter is mandatory emissions equipment that the vehicle was homologated with. Removing it means the car no longer meets the emissions limits it was approved for. This modification cannot be registered in the vehicle documents.
What you risk
- The vehicle will fail the emissions test and the technical inspection.
- At a roadside check, you risk an order to fix the defect, a fine, and in extreme cases the vehicle being taken out of service.
- It can also cause problems with an insurance payout.
The legal alternative
A legal route does exist: a sport catalytic converter with ECE homologation (a less dense substrate than stock, but still a functioning catalytic converter), which offers better flow and sound while still meeting emissions. That route — yes. A decat — no.
Who confirms the vehicle's roadworthiness
Final roadworthiness is confirmed by the STK, or an accredited inspection body. We assess against the regulations actually in force.
- Legal basis
- Act No. 56/2001 Coll., on the operation of vehicles on public roads
- UNECE Regulation No. 83 (vehicle emissions)
- Required paperwork
- None — this modification cannot be legalized by any assessment or registration.
- Inspection/verification
- STK / accredited inspection body / Czech Police (roadside check)