1997 Saturn SL1 DTC P0420

SCARLETKNIGHTS1

MEMBER
1997 SATURN SL1
4 CYL
FWD
AUTOMATIC
52,527 MILES

I am getting a dtc p0420 from the computer. The car is running fine. Does the catalytic converter need to be replaced? Could it be an oxygen sensor? If it is the converter, does the whole assembly need to be replaced or just the main converter itself? Thank you for taking the time to answer.

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

A code P0420 may mean that one or more of the following has happened:

Leaded fuel was used where unleaded was called for
An oxygen sensor is not reading (functioning) properly
The engine coolant temperature sensor is not working properly
Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
Retarded spark timing
The oxygen sensors in front and behind the converter are reporting too similar of readings

Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
Inspect the downstream heated oxygen sensor (HO2), replace if necessary
Replace the catalytic converter