Light on, passes driveability, code P0420. Shop wants a $1,800 cat. Internet says O2 sensor. What’s the smart diagnostic order so I don’t waste money?
One-tap reaction
Diag order (Vic) · Jul 14, 11:00 a.m.
Smart order: confirm code, check for exhaust leaks before the cat, inspect/replace lazy upstream/downstream O2 if aged, only then condemn catalyst. Fuel quality and short trips can trip P0420. Don’t throw a cat at it first — that’s how you donate $1,800.
Riley (Victoria) · Jul 14, 12:00 p.m.
Downstream O2 fixed mine after a shop quoted a cat. Second opinion paid for itself.