How to tell if a catalytic converter or oxygen sensor is bad
An upstream oxygen sensor that fails to fluctuate after fixing oil leaks and misfires typically indicates a ruined catalytic converter alongside a compromised sensor. This prevents the emissions code from clearing permanently, even if the vehicle has technically passed official tailpipe inspections.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1Replacing upstream sensors and catalytic converters
- 2Inspecting internal components of sensors
- 3clearing the error code repeatedly
- 4Clearing the codes repeatedly
- 5Swapping downstream O2 sensors side to side to see if the code follows
- 6Considering hiring a professional mechanic
In their words
Unedited, most upvoted first, each linked to the thread it came from.
“Less than 20 miles have received P0430 code 5-6 times reset every time figuring it was residual from my work because it was driving great otherwise.”source ↗
“My question is do you think this is something I could diagnose and fix myself, or is this a job for the pros?”source ↗
“what else can it be? it passed exhaust emissions tests at the garage and at its last MOT yet it still keeps haunting my car for some reason, regardless of how often i clear it...”source ↗
“Spark plug tips burnt off, submerged under oil from the valve cover leak and a melted coil. I fixed all that and runs great, but sensor one doesn't fluctuate much. Cat almost certainly bad. Sensor one bad too?”source ↗
Where this came up
People with this problem also raised
- 2Catalytic converter clogged without check engine light
- 15How to handle random car error codes and weird driving feelings
- 2Engine smoke and burnt coolant smell while driving
- 2How to test a car ignition switch with a multimeter
- 8Why does a modern car overheat after a few minutes of driving?
- 2Can I drive my car with a stolen catalytic converter?