How the code is set
The engine computer compares upstream and downstream oxygen sensor readings. When the downstream sensor starts mirroring the upstream one, it concludes the converter isn't storing oxygen effectively.
Common causes besides the converter
A lazy downstream O2 sensor, exhaust leaks ahead of the sensor, misfires that overheated the converter, and oil burning can all set P0420.
Repair costs
An oxygen sensor runs about $150–$350 installed. A catalytic converter can cost $600–$2,500+. Proper diagnosis can save you hundreds.
Get it fixed by a mobile mechanic
Matt Mobile Mechanic of Austin handles this at your home anywhere around Austin:
Popular areas: Austin, Round Rock, Pflugerville, Cedar Park, Leander, Georgetown
Frequently Asked Questions
Can I drive with P0420?
Usually yes in the short term, but it can lead to failed emissions inspection.
Will a cleaner fix it?
Rarely for long.
Why are catalytic converters stolen?
They contain valuable platinum, palladium and rhodium.