Catalytic converters
Check anti-pollution system: what it means and what to do
Check anti-pollution system or anti-pollution fault? What it means on Renault, Dacia, Peugeot and Citroën, what to do, and when the cat or DPF is to blame.
Catalytic converters
How catalytic converters work, fail and get replaced.
Catalytic converters
P0420 code: catalyst efficiency below threshold
P0420 means catalyst system efficiency below threshold, bank 1. What sets it, what to check before replacing the catalytic converter, and the MOT rules.
Catalytic converters
What does homologated mean on a catalytic converter or DPF?
Homologated means type approved. When UK law requires a homologated catalytic converter or DPF, what the MOT checks and how to tell if a part qualifies.
Catalytic converters
Failed your MOT on emissions? What to do next
Why vehicles fail the MOT emissions test, what CO, HC, lambda and smoke readings point to, and what to fix before buying a catalytic converter or DPF.
Looking for the basics? Our Help & Advice guides cover how catalytic converters and DPFs work, fitting, the law and warranty.