service engine soon code P4020
#2
Super Moderator
Do you mean p0420? If you do it means Catylyst system efficiency below threshold. I hope thats what you meant and this helps. If this was it I would say replace your Cat converter.
#3
Super Moderator
ROTM Coordinator
ROTM Coordinator
or....
A code P0420 may mean that one or more of the following has happened:
Some suggested steps for troubleshooting a P0420 code include:
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 temperature sensor is not working properly
- Damaged or leaking / catalytic converter / exhaust pipe
- Retarded spark timing
- The oxygen sensors in front and behind the converter are reporting too similar of readings
Some suggested steps for troubleshooting a P0420 code include:
- 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
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#9
Super Moderator
Professional Mechanic
Professional Mechanic
OE cat converters have a mandatory 8 year 80,000 mile warranty from the factory. 99.9% of the time a catalyst efficiency code is a bad cat. You need to be careful some cars have more than one cat. The one the light is referring to has to have a o2 sensor before it and after it.
#10
I have also seen this code be set with an aftermarket O2 sensor POST cat.
Had a customer with a dead O2 sensor, replaced it with a bosch sensor, and they came back the next day with this code. The O2 readings, instead of being dead, it would switch too fast. The post cat O2's are designed to be "lazy". Switched it out with a Delco and never saw it back
Had a customer with a dead O2 sensor, replaced it with a bosch sensor, and they came back the next day with this code. The O2 readings, instead of being dead, it would switch too fast. The post cat O2's are designed to be "lazy". Switched it out with a Delco and never saw it back