Skip the auto shop - Our mechanics make house calls

Q: P0420 code comes back repeatedly, emissions readiness issue. Takes about a week for Check Engine Light to come back on.

asked by on

Repeat code P0420 for Catalyric inefficiency bank 1. However Catalytic and 02 systems show readiness on scanner, Secondary Air system shows not ready.

I have checked for vaccum leaks and fixed a couple. Replace coolant temp sensor and flange becuause of a minor leak. Replaced all spark plugs because of a bad coil. Changed the o2 sensors with OEM Bosch parts.

Also previous owner thought the air pump was bad and replaced it earlier this year.

When I changed the o2s I inspected the Cat. Looks good externally and doesn't make the rattle noise when you shake/hit it.

I have experience working on VW/Audi but this code just keeps on coming back.

I don't want to guess and just change the catalytic if it is not actually bad, but this would be my next diagnostic.

Thanks!

My car has 130000 miles.
My car has a manual transmission.

If this is the only code that keeps coming up, and the data stream on the oxygen sensors are reacting correctly, the only real other thing left would be the convertor. If there was a wiring issue, or a sensor not responding correctly, you should be able to pick that up with the numbers on the scanner.

According to AllDataPro, the suspect would be the convertor due to the fact that P0420 is coming up by itself. If there were additional codes for the oxygen sensors, then there would be other places to look. If you still have doubts about the function of the convertor, you could always perform an exhaust gas diagnosis.

To avoid any unnecessary repairs, have one of our mobile technicians come to your home to perform these checks and properly diagnose the trouble code firsthand.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  • Home
  • Questions
  • P0420 code comes back repeatedly, emissions readiness issue. Takes about a week for Check Engine Light to come back on.

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: How to tell if I need a new catalytic converter

Hey thanks for the question, and thats a really good one by the way. As technology has grown so has the demand for more fuel efficient cars that are more friendly on the environment. One way this is achieved is...

Q: Replaced idle control and throttle sensor now won't idle and service engine light on

Hi there. Check to see if the idle control and throttle position sensor was for your vehicle. Some sensors are universal and can be used on many different vehicles. Check around the sensors to ensure that they are connected. Check...

Q: My car keeps dying while I'm driving - 1999 Mitsubishi Eclipse

Check the transmission range selector for a loose connection and make sure it is tight on the transmission. The code is coming up for the transmission range selector saying that the transmission is in gear and park at the same...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.