I have a 2005 CTS Cadillac with engine came is read p0420 and p0430. What does mean and much will cost me to repair. To recommed any shop in the zip code 78260. Please advice. Thanks, Pete Graham

SOURCE: P0420 and P0430

I have a P0420 code and it seems to be the cat needs replacing.

Mike Butler

• 6674 Answers
• Posted on Jan 25, 2009

SOURCE: 1999 cougar diagnostic code p0430 and p0420

Failed or faulty oxygen sensor, or faulty catalytic converter. It's actually the oxygen sensor reading that the catalytic converter is not functioning properly & needs relacement. That's provided the oxygen sensor is not faulty, which personally, I'd go for that first.
Both would explain excessive fuel usage.

SOURCE: code p0430 p0420

there is a update for the engine computer if you take it in to your toyota dealer they can do it for you. there is a campaign on this issue so its free of charge

SOURCE: P0420 & P0430 codes 99 silverado

codes p0420 and p0430 are both post o2 sensors, the ones after the convertor, both sides if replacing

SOURCE: check engine light-on OBD code's P0420 &

The codes are Catalyst System Efficiency Below Threshold (Bank 1)&(Bank 2).

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

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