Q: Check engine code P0420 and P0420p consistently come up even after erased. Slight smell of fuel when car is stationary.

asked by on February 21, 2017

Trying to diagnose engine code P0420

My car has 118000 miles.
My car has a manual transmission.

Diagnostic trouble code p0420 is for a catalyst efficiency below threshold. Meaning, the control module is receiving a signal that the oxygen sensor is reading a post converter signal that the catalytic converter isn’t doing its job. This could be caused by a converter that has failed, a bad oxygen sensor, or that the engine is running badly enough that the engine control system is operating out of range and can’t make the adjustments necessary to keep the engine running within parameters. I would suggest connecting the vehicle to a diagnostic scanner in order to take a look at the datastream for the oxygen sensors, to check that they are operating within their limits. If this is something you could use a hand in diagnosing/repairing, contact a certified mechanic, like the mobile mechanics at YourMechanic.com.

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